Schwartz's Principles of Surgery - 8th Ed. (2005) – On StatRef

Chapter 41. Neurosurgery - Michael L. Smith, M. Sean Grady

INTRODUCTION

Neurologic surgery is a discipline of medicine and the specialty of surgery that provides the operative and nonoperative management (i.e., prevention, diagnosis, evaluation, treatment, critical care, and rehabilitation) of disorders of the central, peripheral, and autonomic nervous systems, including their supporting structures and vascular supply; the evaluation and treatment of pathologic processes that modify the function or activity of the nervous system, including the hypophysis; and the operative and nonoperative management of pain. As such, neurologic surgery encompasses the treatment of adult and pediatric patients with disorders of the nervous system. These disorders include those of the brain, meninges, skull and skull base, and their blood supply, including surgical and endovascular treatment of disorders of the intracranial and extracranial vasculature supplying the brain and spinal cord; disorders of the pituitary gland; disorders of the spinal cord, meninges, and vertebral column, including those that may require treatment by fusion, instrumentation, or endovascular techniques; and disorders of the cranial and spinal nerves throughout their distribution.

An accurate history is the first step toward neurologic diagnosis. A history of trauma or of neurologic symptoms is of obvious interest, but general constitutional symptoms also are important. Neurologic disease may have systemic effects, while diseases of other symptoms may affect neurologic function. The patient's general medical ability to withstand the physiologic stress of anesthesia and surgery should be understood. A detailed history from the patient and/or family, along with a reliable physical examination will clarify these issues.

NEUROANATOMY

An understanding of neuroanatomy is the foundation of comprehensive neurologic examination and diagnosis. Salient features will be considered, from cephalad to caudad. The cerebral hemispheres (or telencephalon) consist of the cerebral cortex, underlying white matter, the basal ganglia, hippocampus, and amygdala. The cerebral cortex is the most recently evolved part of the nervous system. Its functions are mapped to discrete anatomic areas. The frontal areas are involved in executive function, decision making, and restraint of emotions. The motor strip, or precentral gyrus, is the most posterior component of the frontal lobes, and is arranged along a homunculus with the head inferior and lateral to the lower extremities superiorly and medially. The motor speech area (Broca's area) lies in the left posterior inferior frontal lobe in almost all right-handed people and in up to 90 of left-handed people. The parietal lobe lies between the central sulcus anteriorly and the occipital lobe posteriorly. The postcentral gyrus is the sensory strip, also arranged along a homunculus. The rest of the parietal lobe is involved with awareness of one's body in space and relative to the immediate environment, body orientation, and spatial relationships. The occipital lobes are most posterior. The visual

cortex is arrayed along the apposing medial surfaces of the occipital lobes. The left occipital lobe receives and integrates data from the left half of each retina. A left occipital lesion would therefore result in inability to see objects right of center. The temporal lobes lie below the sylvian fissures. The hippocampus, amygdala, and lower optic radiations (Meyer's loops) are important components of the temporal lobe. They are involved in memory, emotion, and visual pathways, respectively. The receptive speech area (Wernicke's area) lies in the area of the posterior superior temporal lobe and the inferior parietal lobe, usually on the left. The basal ganglia include the caudate, putamen, and the globus pallidus. Basal ganglia structures are involved with modulation of movement via inhibition of motor pathways.

Lying deep to the cerebral hemispheres is the diencephalon, which includes the thalamus and hypothalamus. The thalamus is a key processor and relay circuit for most motor and sensory information going to or coming from the cortex. The hypothalamus, at the base of the brain, is a key regulator of homeostasis, via the autonomic and neuroendocrine systems.

The brain stem consists of the midbrain (mesencephalon), pons (metencephalon), and medulla (myelencephalon). Longitudinal fibers run through the brain stem, carrying motor and sensory information between the cerebral hemispheres and the spinal cord. The corticospinal tract is the major motor tract, while the medial lemniscus and the spinothalamic tracts are the major sensory tracts. The nuclei of cranial nerves III through XII are also located within the brain stem. These nerves relay the motor, sensory, and special sense functions of the eye, face, mouth, and throat. The cerebellum arises from the dorsal aspect of the brain stem. It integrates somatosensory, vestibular, and motor information for coordination and timing of movement. Midline, or vermian, lesions lead to truncal ataxia. Lateral, or hemispheric, lesions lead to tremor and dyscoordination in the extremities.

The ventricular system is a cerebrospinal fluid (CSF)-containing contiguous space inside the brain, continuous with the subarachnoid space outside the brain. The paired lateral ventricles consist of temporal, occipital, and frontal horns, as well as the main body. CSF travels from each lateral ventricle through the foramina of Monroe to the third ventricle, located between the left and right thalami. CSF then drains through the cerebral aqueduct to the fourth ventricle in the brain stem. The foramen of Magendie (midline) and paired foramina of Luschka (lateral) drain to the subarachnoid space. Choroid plexus creates the CSF, mostly in the lateral ventricles. The average adult has an approximate CSF volume of 150 mL and creates approximately 500 mL per day.

The spinal cord starts at the bottom of the medulla and extends through the spinal canal down to approximately the first lumbar vertebra. Motor tracts (efferent pathways) continue from the brain stem down via the lateral and anterior corticospinal tracts to anterior horn cells, and then exit via ventral nerve roots. Sensory information (afferent pathways) enters via dorsal nerve roots, travels up the dorsal columns (proprioception and fine touch) or the spinothalamic tract (pain and temperature) and into the brain stem. Paired nerves exit the spinal cord at each level. There are 31 pairs: 8 cervical, 12 thoracic,

5 lumbar, 5 sacral, and 1 coccygeal.

The dorsal and ventral nerve roots at each level fuse to form mixed motor-sensory spinal nerves and spread through the body to provide innervation to muscles and sensory organs. The C5-T1 spinal nerves intersect in the brachial plexus and divide to form the main nerve branches to the arm, including the median, ulnar, and radial nerves. The L2-S4 spinal nerves intersect in the lumbosacral plexus and divide to form the main nerve branches to the leg, including the common peroneal, tibial, and femoral nerves.

The principal motor tract is the corticospinal tract. It is a two-neuron path, with an upper motor neuron and a lower motor neuron. The upper motor neuron cell body is in the motor strip of the cerebral cortex. The axon travels through the internal capsule to the brain stem, decussates at the brain stem-spinal cord junction, and travels down the contralateral corticospinal tract to the lower motor neuron in the anterior horn at the appropriate level. The lower motor neuron axon then travels via peripheral nerves to its target muscle. Damage to upper motor neurons results in hyperreflexia and mild atrophy. Damage to lower motor neurons results in flaccidity and significant atrophy.

The two major sensory tracts are three-neuron paths. The fine touch and proprioception signals ascend ipsilaterally via the dorsal column, synapse and decussate in the lower medulla, travel up the contralateral medial lemniscus to the second synapse in the thalamus, and then ascend to the sensory cortex. The pain and temperature fibers synapse in the dorsal horn of the spinal cord at their entry level, decussate, and travel up the contralateral spinothalamic tracts to the thalamus. The second synapse occurs in the thalamus, and the output ascends to the sensory cortex.

The nervous system is composed of the somatic nervous system and the autonomic nervous system (ANS). The motor and sensory tracts described so far compose the former. The latter carries messages for homeostasis and visceral regulation from the central nervous system (CNS) to target structures such as arteries, veins, the heart, sweat glands, and the digestive tract.1 CNS control of the ANS arises particularly from the hypothalamus and the nucleus of the tractus solitarius. The ANS is divided into the sympathetic, parasympathetic, and enteric systems. The sympathetic system drives the "fight or flight" response, and uses epinephrine to increase heart rate, blood pressure, blood glucose, and temperature, and to dilate the pupils. It arises from the thoracolumbar spinal segments. The parasympathetic system promotes the "rest and digest" state, and uses acetylcholine to maintain basal metabolic function under nonstressful circumstances. It arises from cranial nerves III, VII, IX, and X, and from the second to fourth sacral segments. The enteric nervous system controls the complex synchronization of the digestive tract, especially the pancreas, gallbladder, and small and large bowels. It can run autonomously, but is under the regulation of the sympathetic and parasympathetic systems.

NEUROLOGIC EXAMINATION

Introduction

The neurologic examination is divided into several components and is generally done from head to toe. First assess mental status. A patient may be awake, lethargic (will follow commands and answer questions, but then returns to sleep), stuporous (difficult to arouse at all), or comatose (no purposeful response to voice or pain). Cranial nerves may be thoroughly tested in the awake patient, but pupil reactivity, eye movement, facial symmetry, and gag are the most relevant when mental status is impaired. Motor testing is based on maximal effort of major muscle groups in those able to follow commands, while assessing for amplitude and symmetry of movement to deep central pain may be all that is possible for stuporous patients. Table 41-1 details scoring for motor assessment tests. Characteristic motor reactions to pain in patients with depressed mental status include withdrawal from stimulus, localization to stimulus, flexor (decorticate) posturing, extensor (decerebrate) posturing, or no reaction (in order of worsening pathology). Figure 41-1 diagrams the clinical patterns of posturing. This forms the basis of determining the Glasgow Coma Scale motor score, as detailed in Table 41-2. Light touch, proprioception, temperature, and pain testing may be useful in awake patients but is often impossible without good cooperation. It is critical to document sensory patterns in spinal cord injury patients. Muscle stretch reflexes should be checked. Often comparing left to right or upper extremity to lower extremity reflexes for symmetry is the most useful for localizing a lesion. Check for ankle-jerk clonus or up-going toes (the Babinski test). Presence of either is pathologic and signifies upper motor neuron disease.

Diagnostic Studies

Plain Films

Plain x-rays of the skull may demonstrate fractures, osteolytic or osteoblastic lesions, or pneumocephaly (air in the head). The use of skull plain films has decreased given the rapid availability and significantly increased detail of head computed tomography (CT) scans. Plain films of the cervical, thoracic, and lumbar spine are used to assess for evidence of bony trauma or soft-tissue swelling suggesting fracture. Spinal deformities and osteolytic or osteoblastic pathologic processes also will be apparent. The shoulder girdle usually poses problems in visualizing the cervicothoracic junction clearly.

Computed Tomography

The noncontrast CT scan of the head is an extremely useful diagnostic tool in the setting of new focal neurologic deficit, decreased mental status, or trauma. It is rapid and almost universally available in hospitals in the United States. Its sensitivity allows for the detection of acute hemorrhage. A contrast-enhanced CT scan will help show neoplastic or infectious processes. In the current era, contrast CT is generally used for those patients who cannot undergo magnetic resonance imaging (MRI) scanning due to pacemakers or metal in the orbits. Fine-slice CT scanning of the spine is helpful for defining bony anatomy and pathology, and is usually done after an abnormality is seen on plain films, or because plain films are inadequate (especially to visualize C7 and T1 vertebrae). Finally, high-speed multislice scanners, combined with timed-bolus contrast injections,

allow CT-angiography (CT-A). A thin-slice axial scan is obtained during the passage of contrast through the cerebral arteries and reconstructed in 3-D to assess for vascular lesions. CT-A does not reliably detect lesions, such as cerebral aneurysms, less than 3 mm across, but can provide detailed morphologic data of larger lesions. Newer, multislice scanner technology is approaching the resolution of conventional angiography.

Magnetic Resonance Imaging

MRI provides excellent imaging of soft tissue structures in the head and spine. It is a complex and evolving science. Several of the most clinically useful MRI sequences are worth describing. T1 sequences made before and after gadolinium administration are useful for detecting neoplastic and infectious processes. T2 sequences facilitate assessment of neural compression in the spine by the presence or absence of bright T2 CSF signals around the cord or nerve roots. Diffusion-weighted images (DWI) can detect ischemic stroke earlier than CT. Fine-slice time-of-flight (TOF) axial images can be reformatted in three dimensions to build MRI-angiograms (MR-A) and MRI-venograms (MR-V). MR-A can detect stenosis of the cervical carotid arteries or intracranial aneurysms greater than 3 mm in diameter. MR-V can assess the sinuses for patency or thrombosis.

Angiography

Transarterial catheter-based angiography remains the gold standard for evaluation of vascular pathology of the brain and spine. The current state of the art is biplanar imaging to reduce dye load and facilitate interventional procedures. Digital subtraction technologies minimize bony interference in the resultant images. Bilateral carotid arteries and bilateral vertebral arteries may be injected and followed through arterial, capillary, and venous phases for a complete cerebral angiogram.

Electromyography and Nerve Conduction Studies

Electromyography and nerve conduction studies (EMG and NCS) are useful for assessing the function of peripheral nerves. EMG records muscle activity in response to a proximal stimulation of the motor nerve. NCS records the velocity and amplitude of the nerve action potential. EMG/NCS is typically performed approximately 4 weeks after an acute injury, as nerves distal to the injury continue to transmit electrical impulses normally until degeneration of the distal nerve progresses.

Invasive Monitoring

There are several methods of monitoring intracranial physiology. The three described here are bedside intensive care unit (ICU) procedures and allow continuous monitoring. All three involve making a small hole in the skull with a hand-held drill. They are generally placed in the right frontal region to minimize the neurologic impact of possible complications, such as hemorrhage. The most reliable monitor, always, is an alert patient

with a reliable neurologic exam. If a reliable neurologic exam is not possible due to the presence of brain injury, sedatives, or paralytics, and there is active and unstable intracranial pathology, then invasive monitoring is required.

External Ventricular Drain (EVD). An EVD is also known as a ventriculostomy. A perforated plastic catheter is inserted into the frontal horn of the lateral ventricle. An uninterrupted fluid column through a rigid tube allows transduction of intracranial pressure (ICP). CSF also can be drained to reduce ICP or sampled for laboratory studies.

Intraparenchymal Fiberoptic Pressure Transducer. This device is commonly referred to as a "bolt." Again, a small hole is drilled in the skull. A threaded post locks securely into the skull and holds the fiberoptic catheter in place. A bolt allows ICP monitoring only, but is smaller and less invasive than a ventriculostomy, and may be associated with fewer complications, although the data are not clear.

Brain Tissue Oxygen Sensors. The brain tissue oxygen sensor is a recent development. The device is screwed into the skull in the same manner as the bolt; however, the sensor catheter is an electrochemical oxygen-tension sensitive membrane. A single bolt can be designed to accept a pressure sensor, oxygen sensor, and brain temperature sensor. Patients with severe brain injury due to trauma or aneurysmal hemorrhage may benefit from placement of these three sensors and a ventriculostomy to drain CSF for control of ICP. This requires two twist-drill holes, which may be adjacent or on opposite sides of the head.

NEUROLOGIC AND NEUROSURGICAL EMERGENCIES

Raised Intracranial Pressure

ICP normally varies between 4 and 14 mm Hg. Sustained ICP levels above 20 mm Hg can injure the brain. The Monro-Kellie doctrine states that the cranial vault is a rigid structure, and therefore the total volume of the contents determines ICP. The three normal contents of the cranial vault are brain, blood, and CSF. The brain's contents can expand due to swelling from traumatic brain injury (TBI), stroke, or reactive edema. Blood volume can increase by extravasation to form a hematoma, or by reactive vasodilation in a hypoventilating, hypercarbic patient. CSF volume increases in the setting of hydrocephalus. Figure 41-2 demonstrates classic CT findings of hydrocephalus. Addition of a fourth element, such as a tumor or abscess, will also increase ICP. The pressure-volume curve depicted in Fig. 41-3 demonstrates a compensated region with a small P/V, and an uncompensated region with large P/V. In the compensated region, increased volume is offset by decreased volume of CSF and blood.

Increased ICP can injure the brain in several ways. Focal mass lesions cause shift and herniation. Temporal lesions push the uncus medially and compress the midbrain. This is known as uncal herniation. The posterior cerebral artery passes between the uncus and midbrain and may be occluded, leading to occipital infarct. Masses higher up in the hemisphere can push the cingulate gyrus under the falx cerebri. This is known as

subfalcine herniation. The anterior cerebral artery branches run along the medial surface of the cingulate gyrus and may be occluded, leading to medial frontal and parietal infarcts. Diffuse increases in pressure in the cerebral hemispheres can lead to central, or transtentorial, herniation. Increased pressure in the posterior fossa can lead to upward central herniation or downward tonsillar herniation through the foramen magnum. Uncal, transtentorial, and tonsillar herniation can cause direct damage to the very delicate brain stem. Figure 41-4 diagrams patterns of herniation.

Patients with increased ICP, also called intracranial hypertension (ICH), will often present with headache, nausea, vomiting, and progressive mental status decline. Cushing's triad is the classic presentation of ICH: hypertension, bradycardia, and irregular respirations. This triad is usually a late manifestation. Focal neurologic deficits may also be present if there is a focal mass lesion causing the problem. Patients with these symptoms should have a head CT as soon as possible.

Initial management of ICH includes airway protection and adequate ventilation. A bolus of mannitol up to 1 g/kg causes free water diuresis, increased serum osmolality, and extraction of water from the brain. The effect is delayed by about 20 minutes and has a transient benefit. Driving serum osmolality above 300 mOsm/L is of indeterminate benefit and can have deleterious cardiovascular side effects, such as hypovolemia that leads to hypotension and decreased brain perfusion. Cases of ICH usually need rapid neurosurgical evaluation. Ventriculostomy or craniotomy may be needed for definitive decompression.

It is critical to note that lethargic or obtunded patients often have decreased respiratory drive. This causes the partial pressure of arterial carbon dioxide (PaCO2) to increase, resulting in cerebral vasodilation and worsening of ICH. This cycle causes a characteristic "crashing patient," who rapidly loses airway protection, becomes apneic, and herniates. Emergent intubation and ventilation to reduce PaCO2 to roughly 35 mm Hg can reverse the process and save the patient's life.

Brain Stem Compression

Disease in the posterior fossa (brain stem and cerebellum) requires special consideration. The volume of the posterior fossa is small. Hemorrhage or stroke in the posterior fossa causes mass effect and can rapidly kill the patient in two ways. Occlusion of the fourth ventricle causes acute obstructive hydrocephalus, leading to raised ICP, herniation, and then death. The mass effect can also lead directly to brain stem compression (Fig. 41-5). Symptoms of brain stem compression include progressive obtundation and hypertension, followed rapidly by brain death. A patient with evidence of either or both needs emergent neurosurgical evaluation for possible ventriculostomy and suboccipital craniectomy (removal of the bone covering the cerebellum). This situation is especially critical, as expeditious decompression can lead to significant functional recovery of patients who present near brain death.

Stroke

Patients who present with acute focal neurologic deficits for whom the time of onset of symptoms can be clearly defined (i.e., when the patient was last seen in a normal state of health) must be evaluated as rapidly as possible. An emergent head CT scan should be done. This is often normal, because CT changes from ischemic stroke may take up to 24 hours to appear (Fig. 41-6). A patient with a clinical diagnosis of acute stroke less than 3 hours old, without hemorrhage on CT, may be a candidate for thrombolytic therapy with tissue plasminogen activator (tPA).

Seizure

A seizure is defined as uncontrolled neuronal electrical activity. New-onset seizure often signifies an irritative mass lesion in the brain. Tumors commonly present with seizure. Patients with traumatic intracranial hemorrhage are at risk for seizure. A seizing patient is at risk for neural damage if the seizure is not stopped, as well as airway and ventilation problems. Any patient with new-onset seizure should have imaging of the brain, such as a head CT scan, after the seizure is controlled and the patient resuscitated.

TRAUMA

Introduction

Trauma is the leading cause of death in children and young adults; however, incidences of death and disability from trauma have been slowly decreasing. This is partly attributable to increased awareness of the importance of using seat belts and bicycle and motorcycle helmets. However, trauma remains a major cause of morbidity and mortality, and can affect every major organ system in the body. The three main areas of neurosurgic interest in trauma are TBI, spine and spinal cord injury (SCI), and peripheral nerve injury.

Head Trauma

Glasgow Coma Scale (GCS) Score

The initial assessment of the trauma patient includes the primary survey, resuscitation, secondary survey, and definitive care. Neurosurgical evaluation begins during the primary survey with the determination of the GCS score (usually referred to simply as the GCS) for the patient. The GCS is determined by adding the scores of the best responses of the patient in each of the three categories. The motor score ranges from 1 to 6, verbal from 1 to 5, and eyes from 1 to 4. The GCS therefore ranges from 3 to 15, as detailed in Table 41-2.

Scalp Injury

Blunt or penetrating trauma to the head can cause injury to the densely vascularized scalp, and significant blood loss can occur. Direct pressure initially controls the bleeding,

allowing close inspection of the injury. If a simple laceration is found, it should be copiously irrigated and closed primarily. If the laceration is short, a single-layer percutaneous suture closure will suffice. If the laceration is long or has multiple arms, the patient may need debridement and closure in the operating room, with its superior lighting and wider selection of instruments and suture materials. Careful reapproximation of the galea will provide a more secure closure and better hemostasis. Blunt trauma can also cause crush injury with subsequent tissue necrosis. These wounds require debridement and consideration of advancement flaps to cover the defect.

Skull Fractures

The usual classification system for bone fractures may be applied to the skull. Characterization may be done using skull x-rays or head CT.2 A closed fracture is covered by intact skin. An open, or compound, fracture is associated with disrupted overlying skin. The fracture lines may be single (linear); multiple and radiating from a point (stellate); or multiple, creating fragments of bone (comminuted). Closed skull fractures do not normally require specific treatment. Open fractures require repair of the scalp. Skull fractures in general indicate that a significant amount of force was transmitted to the head, and should increase the suspicion for intracranial injury. Fractures that cross meningeal arteries can cause rupture of the artery and subsequent epidural hematoma formation.

Depressed skull fractures may result from a focal injury of significant force. The inner and outer cortices of the skull are disrupted, and a fragment of bone is pressed in toward the brain in relation to adjacent intact skull. The fragment may overlap the edge of intact bone, or may plunge completely below the level of adjacent normal skull. The inner cortex of the bone fragments often has multiple sharp edges that can lacerate dura, brain, and vessels. Craniotomy is required to elevate the fracture, repair dural disruption, and obtain hemostasis in these cases (Fig. 41-7). Fractures overlying dural venous sinuses require restraint. Surgical exploration can lead to life-threatening hemorrhage from the lacerated sinus.

Fractures of the skull base are common in head-injured patients, and they indicate significant impacts. They are generally apparent on routine head CT, but should be evaluated with dedicated fine-slice coronal-section CT scan to document and delineate the extent of the fracture and involved structures. If asymptomatic, they require no treatment. Symptoms from skull base fractures include cranial nerve deficits and CSF leaks. A fracture of the temporal bone, for instance, can damage the facial or vestibulocochlear nerve, resulting in vertigo, ipsilateral deafness, or facial paralysis. A communication may be formed between the subarachnoid space and the middle ear, allowing CSF drainage into the pharynx via the eustachian tube or from the ear (otorrhea). Extravasation of blood results in ecchymosis behind the ear, known as Battle's sign. A fracture of the anterior skull base can result in anosmia (loss of smell from damage to the olfactory nerve), CSF drainage from the nose (rhinorrhea), or periorbital ecchymoses, known as raccoon eyes.

Copious clear drainage from the nose or ear makes the diagnosis of CSF leakage obvious. Often, however, the drainage may be discolored with blood or small in volume if some drains into the throat. The halo test can help differentiate. Allow a drop of the fluid to fall on an absorbent surface such as a facial tissue. If blood is mixed with CSF, the drop will form a double ring, with a darker center spot containing blood components surrounded by a light halo of CSF. If this is indeterminate, the fluid can be sent to the lab for beta-transferrin testing. Beta-transferrin testing will only be positive if CSF is present.

Many CSF leaks will heal with elevation of the head of the bed for several days. A lumbar drain can augment this. A lumbar drain is a catheter placed in the lumbar CSF cistern to decompress the cranial vault and allow the defect to heal by eliminating normal hydrostatic pressure. There is no proven efficacy of antibiotic coverage for preventing meningitis in patients with CSF leaks.

Traumatic cranial neuropathies are generally managed conservatively, with documentation of the extent of impairment and signs of recovery. Patients with traumatic facial nerve palsies may benefit from a course of steroids, although their benefit is unproven. Patients with facial nerve palsy of abrupt onset, who do not respond to steroids within 48 to 72 hours may be considered for surgical decompression of the petrous portion of the facial nerve. Patients may also present with delayed-onset facial nerve palsy. Again, steroids are employed and surgery is considered, with mixed results.

Closed Head Injury

Closed head injury (CHI) is the most common type of TBI, and a significant cause of morbidity and mortality in the United States. There are two important factors that affect the outcome in CHI and TBI in general. The initial impact causes the primary injury, defined as the immediate injury to neurons from transmission of the force of impact. The long, delicate axons of the neurons can shear as the different areas of the brain through which they pass accelerate and decelerate at different speeds. Prevention strategies, such as wearing helmets, remain the best means to decrease disability from primary injury. Subsequent neuronal damage due to the sequelae of trauma is referred to as secondary injury. Hypoxia, hypotension, hydrocephalus, intracranial hypertension, and intracranial hematoma are all mechanisms of secondary injury. The focus of basic research into brain trauma, critical care medicine, and neurosurgical intervention is to decrease the effects of secondary injury.

The Brain Trauma Foundation released, with the approval of the American Association of Neurological Surgeons, an updated summary of management recommendations for brain-injured patients in 2000. The guidelines standardize the care of these patients with the hope of improving outcomes. Some of the common patterns of CHI, including concussion, contusion, and diffuse axonal injury, are discussed below.

Initial Assessment. The initial evaluation of a trauma patient remains the same whether or not the primary surveyor suspects head injury. The first three elements of the ABCDs of resuscitation, airway, breathing, and circulation, must first be assessed and stabilized.

Hypoxia and hypotension worsen outcome in TBI (due to secondary injury), so cardiopulmonary stabilization is critical. Patients who cannot follow commands require intubation for airway protection and ventilatory control. The fourth element, assessment of the D, for disability, is undertaken next. Motor activity, speech, and eye opening can be assessed in a few seconds and a GCS assigned.

An efficient way for the primary surveyor to assess disability and ascertain the status of the three components of the GCS follows. Approach the patient and enter his or her field of view. Observe whether the patient visually orients to you. Clearly command: "Tell me your name." Then ask the patient to lift up two fingers on each side sequentially, and wiggle the toes. A patient not responsive to these prompts should be assessed for response to deep central painful stimulus, with a firm, twisting pinch of the sensitive skin above the clavicle. Watch for eye opening and movement of the extremities, whether purposeful or reflex. Assess the verbal response. The motor, verbal, and eye-opening scores may be correctly assigned using this rapid examination, and an initial assessment of the probability of significant head injury made. Also take note of any external signs of head injury, including bleeding from the scalp, nose, or ear, or deformation of the skull or face.

Medical Management. Several medical steps may be taken to minimize secondary neuronal injury and the systemic consequences of head injury. Patients with a documented closed head injury should receive a 17-mg/kg phenytoin loading dose, followed by 1 week of therapeutic maintenance phenytoin, typically 300 to 400 mg/d. Phenytoin prophylaxis has been shown to decrease the incidence of early posttraumatic seizures. There is no evidence to support longer-term use of prophylactic antiepileptic agents. Blood glucose levels should be closely monitored by free blood sugar checks and controlled with sliding scale insulin. Fevers should also be evaluated and controlled with antipyretics, as well as source-directed therapy when possible. Hyperglycemia and hyperthermia are toxic to injured neurons, and so contribute to secondary injury. Head-injured patients have an increased prevalence of peptic ulceration and gastrointestinal (GI) bleeding. Peptic ulcers occurring in patients with head injury or high ICP are referred to as Cushing's ulcers, and may be related to hypergastrinemia. Ulcer prophylaxis should be used. Compression stockings or athrombic pumps should be used when the patient cannot be mobilized rapidly.

Classification. Head injury can be classified as mild, moderate, or severe. For patients with a history of head trauma, classification is as follows: severe head injury if the GCS is 3 to 8, moderate head injury if the GCS is 9 to 12, and mild head injury if the GCS is 13 to 15. Many people present to emergency rooms and trauma bays with a history of head trauma, so a triage system must be employed to maximize resource utilization while minimizing the chance of missing occult or progressing injuries.

Head trauma patients who are asymptomatic; who have only headache, dizziness, or scalp lacerations or abrasions; or who did not lose consciousness have a low risk for intracranial injury and may be discharged home without a head CT scan.3,4 Head-injured patients who are discharged should be sent home with reliable family or friends who can

observe the patient for the first postinjury day. Printed discharge instructions, which describe monitoring for confusion, persistent nausea, weakness, or speech difficulty, should be given to the caretaker. The patient should return to the emergency department for evaluation of such symptoms.

Patients with a history of altered or lost consciousness, amnesia, progressive headache, skull or facial fracture, vomiting, or seizure have a moderate risk for intracranial injury and should undergo prompt head CT. If the CT is normal, and the neurologic exam has returned to baseline (excluding amnesia of the event), then the patient can be discharged to the care of a responsible adult, again with printed criteria for returning to the ER. Otherwise the patient must be admitted for a 24-hour observation period.

Patients with depressed consciousness, focal neurologic deficits, penetrating injury, depressed skull fracture, or changing neurologic exam have a high risk for intracranial injury. These patients should undergo immediate head CT and admission for observation or intervention as needed.

Concussion. A concussion is temporary neuronal dysfunction after nonpenetrating head trauma. The head CT is normal, and deficits resolve over minutes to hours. Definitions vary; some require transient loss of consciousness, while others include patients with any alteration of mental status. Memory difficulties, especially amnesia of the event, are very common. Concussions may be graded. One method is the Colorado Medical Society system. Head trauma patients with confusion only are grade 1, patients with amnesia are grade 2, and patients who lose consciousness are grade 3. Studies have shown that the brain remains in a hypermetabolic state for up to a week after injury. The brain is also much more susceptible to injury from even minor head trauma in the first 1 to 2 weeks after concussion. This is known as second-impact syndrome, and patients should be informed that even after mild head injury they might experience memory difficulties or persistent headaches.5

Contusion. A contusion is a bruise of the brain, and occurs when the force from trauma is sufficient to cause breakdown of small vessels, and extravasation of blood into the brain. The contused areas appear bright on CT scan, as seen in Fig. 41-8. The frontal, occipital, and temporal poles are most often involved. The brain sustains injury as it moves in relation to rough bony surfaces. Contusions themselves rarely cause significant mass effect as they represent small amounts of blood in injured parenchyma rather than coherent blood clots. Edema may develop around a contusion, causing mass effect. Contusions may also enlarge, or develop a true hematoma, especially during the first 24 hours. Contusions may also be seen in brain tissue opposite the site of impact. This is known as a contre coup injury. These contusions result from deceleration of the brain against the skull.

Diffuse Axonal Injury. Diffuse axonal injury is caused by damage to axons throughout the brain, due to rotational acceleration and then deceleration. Axons may be completely disrupted and then retract, forming axon balls. Small hemorrhages can be seen in more severe cases, especially on MRI. Hemorrhage is classically seen in the corpus callosum

and the dorsolateral midbrain.

Penetrating Injury. These are complex and must be evaluated individually. The two main subtypes are missile injury (e.g., due to bullets or fragmentation devices) and nonmissile injury (e.g., due to knives or ice picks). Some general principles do apply. If available, skull x-rays and CT scans are useful in assessing the nature of the injury. Cerebral angiography must be considered if the object passes near a major artery or dural venous sinus. Operative exploration is necessary to remove any object extending out of the cranium, as well as for debridement, irrigation, hemostasis, and definitive closure. Small objects contained within brain parenchyma are often left in place to avoid iatrogenic secondary brain injury. Antibiotics are given to decrease the chances of meningitis or abscess formation. High-velocity missile injuries (from high-powered hunting rifles or military weapons) are especially deadly, because the associated shock wave causes cavitary tissue destruction of an area that is much larger than the projectile itself. Projectiles that penetrate both hemispheres or traverse the ventricles are almost universally fatal.

Traumatic Intracranial Hematomas

The various traumatic intracranial hematomas contribute to death and disability secondary to head injury. Hematomas can expand rapidly and cause brain shifting and subsequent herniation. Emergent neurosurgical evaluation and intervention are often necessary.

Epidural Hematoma. Epidural hematoma (EDH) is the accumulation of blood between the skull and the dura. EDH usually results from arterial disruption, especially of the middle meningeal artery. The dura is adherent to bone and some pressure is required to dissect between the two. EDH has a classic three-stage clinical presentation that is probably seen in only 20 of cases. The patient is initially unconscious from the concussive aspect of the head trauma. The patient then awakens and has a lucid interval while the hematoma subclinically expands. As the volume of the hematoma grows, the decompensated region of the pressure-volume curve is reached, the ICP increases, and the patient becomes lethargic and herniates. Uncal herniation from an EDH classically causes ipsilateral third nerve palsy and contralateral hemiparesis.

On head CT the clot is bright, biconvex (lentiform), and has a well-defined border that usually respects cranial suture lines. The clot generally forms over the convexities, but may rarely occur in the posterior fossa as well.

Open craniotomy for evacuation of the congealed clot and hemostasis is indicated for EDH, except in selected cases of asymptomatic clots that are less than 1 cm in maximum thickness, seen in patients with a negative neurologic examination. Prognosis after successful evacuation is better for epidural hematoma than subdural hematoma. EDHs are associated with lower-energy trauma with less resultant primary brain injury. Good outcomes may be seen in 85 to 90 of patients, with rapid CT scan and intervention.

Acute Subdural Hematoma. An acute subdural hematoma (SDH) is the result of an accumulation of blood between the arachnoid membrane and the dura. Acute SDH usually results from venous bleeding, usually from tearing of a bridging vein running from the cerebral cortex to the dural sinuses. The bridging veins are subject to stretching and tearing during acceleration/deceleration of the head, because the brain shifts in relation to the dura, which firmly adheres to the skull. Elderly and alcoholic patients are at higher risk for acute SDH formation after head trauma due to the greater mobility of their atrophied brains within the cranial vault.

On head CT scan, the clot is bright or mixed-density, crescent-shaped (lunate), may have a less distinct border, and does not cross the midline due to the presence of the falx. Most SDHs are over the cerebral hemispheres, but they may also layer on the tentorium or be interhemispheric.

Open craniotomy for evacuation of the clot is indicated for any acute SDH more than 1 cm in thickness, or smaller hematomas that are symptomatic. Symptoms may be as subtle as a contralateral pronator drift, or as dramatic as coma. Smaller hematomas may stabilize and eventually reabsorb, or become chronic SDHs. Nonoperatively managed patients require frequent neurologic exams until stabilization of the clot if proven by serial head CT scans.

The prognosis for functional recovery is significantly worse for acute SDH than EDH, because it is associated with greater primary injury to brain parenchyma from high-energy impacts. Prompt recognition and intervention minimizes secondary injury. Elderly patients, patients with low admission GCS, or high postoperative ICP do poorly, with as few as 5 attaining functional recovery.6

Chronic Subdural Hematoma. Chronic SDH is a collection of blood breakdown products that is at least 3 weeks old. Acute hematomas are bright white (hyperdense) on CT scan for approximately 3 days, after which they fade to isodensity with brain, and then to hypodensity after 2 to 3 weeks. A true chronic SDH will be as dark as CSF on CT. Traces of white are often seen due to small hemorrhages into the collection. These small bleeds may expand the collection enough to make it symptomatic. This is referred to as acute-on-chronic SDH. Figure 41-9 demonstrates the CT appearance of an acute-on-chronic SDH. Vascularized membranes form within the hematoma as it matures. These membranes may be the source of acute hemorrhage.

Chronic SDHs often occur in patients without a clear history of head trauma, as they may arise from minor trauma. Alcoholics, the elderly, and patients on anticoagulation are at higher risk for developing chronic SDH. Patients may present with headache, seizure, confusion, contralateral hemiparesis, or coma.

A chronic SDH thicker than 1 cm, or any symptomatic SDH should be surgically drained. Unlike acute SDH, which consists of a thick, congealed clot, chronic SDH typically consists of a viscous fluid, with a texture and the dark brown color reminiscent of motor oil. As such, a simple burr hole can effectively drain most chronic SDHs. There remains

controversy about the optimum treatment of chronic SDH, but most authorities agree that burr hole drainage should be attempted first, to obviate the risks of formal craniotomy. A single burr hole placed over the dependent edge of the collection can be made, and the space copiously irrigated until the fluid is clear. A second, more anterior, burr hole can then be placed if the collection does not drain satisfactorily due to containment by membranes. The procedure is converted to open craniotomy if the SDH is too congealed for irrigation drainage, the complex of membranes prevents effective drainage, or persistent hemorrhage occurs that cannot be reached with bipolar cautery through the burr hole. The required surgical prepping and draping are always performed to allow simple conversion to craniotomy, and the incisions and burr holes placed to allow easy incorporation into question mark-shaped craniotomy flaps.

There are various strategies to prevent reaccumulation of blood. Subdural or subgaleal drains may be left in place for 1 to 2 days. Mild hydration and bedrest with the head of bed flat may encourage brain expansion. High levels of inspired oxygen may help draw nitrogen out of the cavity. Regardless of the strategy used, follow-up head CT scans are required immediately postoperatively and approximately 1 month later to document resolution.

Intraparenchymal Hemorrhage. Isolated hematomas within the brain parenchyma are more often associated with hypertensive hemorrhage or arteriovenous malformations. Bleeding may occur in a contused area of brain. Mass effect from developing hematomas may present as delayed neurologic deficit. Delayed traumatic intracerebral hemorrhage is most likely to occur within the first 24 hours. Patients with contusion on the initial head CT scan should be reimaged 24 hours after the trauma to document stable pathology.

Vascular Injury

Trauma to the head or neck may cause damage to the carotid or vertebrobasilar systems. In general usage, dissection refers to violation of the vessel wall intima. Blood at arterial pressure can then open a plane between the intima and media, within the media, or between the media and adventitia. The newly created space within the vessel wall is referred to as the false lumen. Tissue or organs supplied by traumatically-dissected vessels may subsequently be injured in several ways. Expansion of the hematoma within the vessel wall can lead to narrowing of the true vessel lumen and reduction or cessation of distal blood flow. Slow-flowing or stagnant blood within the false lumen exposed to thrombogenic vessel wall elements may thrombose. Pieces of thrombus may then detach and cause distal embolic arterial occlusion. Also, the remaining partial-thickness vessel wall may rupture, damaging adjacent structures.

Traumatic dissection may occur in the carotid artery (anterior circulation) or the vertebral or basilar arteries (posterior circulation). Dissections may be extradural or intradural. Intradural dissection can present with subarachnoid hemorrhage, whereas extradural dissection cannot.

Traditional angiography remains the basis of diagnosis and characterization of arterial

dissection. Angiographic abnormalities include stenosis of the true lumen, visible intimal flaps, and the appearance of contrast in the false lumen. Four-vessel cerebral angiography should be performed when suspicion of dissection exists.

Patients with documented arterial dissection should be anticoagulated with heparin and then warfarin to prevent thromboembolic stroke. Trauma patients often have concomitant absolute or relative contraindications to anticoagulation, complicating management. Warfarin may be discontinued when the angiogram normalizes, or after several months. Consider surgical intervention for persisting embolic disease and for vertebral dissections presenting with subarachnoid hemorrhage. Surgical options include vessel ligation and bypass grafting. Interventional radiology techniques include stenting and vessel occlusion. Occlusion techniques depend on good collateral circulation to perfuse the vascular territory previously supplied by the occluded vessel.

Carotid Dissection. Carotid dissection may result from neck extension combined with lateral bending to the opposite side, or trauma from an incorrectly placed shoulder belt tightening across the neck in a motor vehicle accident. Extension/bending stretches the carotid over the bony transverse processes of the cervical vertebrae, while seat belt injuries cause direct trauma. Symptoms of cervical carotid dissection include contralateral neurologic deficit from brain ischemia, headache, and ipsilateral Horner's syndrome from disruption of the sympathetic tracts ascending from the stellate ganglion into the head on the surface of the carotid artery. The patient may complain of hearing or feeling a bruit.

Traumatic vessel wall injury to the portion of the carotid artery running through the cavernous sinus may result in a carotid-cavernous fistula (CCF). This creates a high-pressure, high-flow pathophysiologic blood flow pattern. CCFs classically present with pulsatile proptosis (the globe pulses outward with arterial pulsation), retro-orbital pain, and decreased visual acuity or loss of normal eye movement (due to damage to cranial nerves III, IV, and VI as they pass through the cavernous sinus). Symptomatic CCFs should be treated to preserve eye function. Fistulae may be closed by balloon occlusion using interventional neuroradiology techniques. Fistulae with wide necks are difficult to treat and may require total occlusion of the parent carotid artery.

Vertebrobasilar Dissection. Vertebrobasilar dissection may result from sudden rotation or flexion/extension of the neck, chiropractic manipulation, or a direct blow to the neck. Common symptoms are neck pain, headache, and brain stem stroke or subarachnoid hemorrhage. Treatment is as described above.

Brain Death

Brain death occurs when there is an absence of signs of brain stem function or motor response to deep central pain in the absence of pharmacologic or systemic medical conditions that could impair brain function.

Clinical Examination. A neurologist, neurosurgeon, or intensivist generally performs the

clinical brain death exam. Two exams consistent with brain death 12 hours apart, or one exam consistent with brain death followed by a consistent confirmatory study is generally sufficient to declare brain death (see below). Hospital regulations and local laws regarding documentation should be followed closely.

Establish the absence of complicating conditions before beginning the exam. The patient must be normotensive, euthermic, and oxygenating well. The patient may not be under the effects of any sedating or paralytic drugs.

Documentation of no brain stem function includes the following: nonreactive pupils; lack of corneal blink, oculocephalic (doll's eyes), or oculovestibular (cold calorics) reflexes; and loss of drive to breathe (apnea test). The apnea test demonstrates no spontaneous breathing even when PaCO2 is allowed to rise above 60 mm Hg.

Deep central painful stimulus is provided by forceful twisting pinch of the sensitive skin above the clavicle. Pathologic responses such as flexor or extensor posturing are not compatible with brain death. Spinal reflexes to peripheral pain, such as triple flexion of the lower extremities, are compatible with brain death.

Confirmatory Studies. Confirmatory studies are performed after a documented clinical exam consistent with brain death. A study consistent with brain death may obviate the need to wait 12 hours for a second exam. This is especially important when the patient is a potential organ donor, as brain dead patients often have progressive hemodynamic instability. Lack of cerebral blood flow consistent with brain death may be documented by cerebral angiography or technetium radionuclide study. A"to-and-fro" pattern on transcranial Doppler (TCD) ultrasonography indicates no net forward flow through the cerebral vasculature, consistent with brain death. An electroencephalogram (EEG) documenting electrical silence has been used, but is generally not favored because there is often artifact or noise on the recording. This can confuse the situation and be especially difficult for families to understand.

Spine Trauma

The spine is a complex biomechanic and neural structure. The spine provides structural support for the body as the principal component of the axial skeleton, while protecting the passing spinal cord and nerve roots. Trauma may fracture bones or cause ligamentous disruption. Often bone and ligament damage occur together. Damage to these elements reduces the strength of the spine and may cause the spine to be unstable. This compromises both its structural support function and its ability to protect neural elements. Spine trauma may occur with or without neurologic injury. Neurologic injury from spine trauma is classified as either incomplete, if there is some residual motor or sensory neurologic function below the level of the lesion, or complete, if there is no residual neurologic function below the level of the lesion, as assessed by clinical exam.7 A patient with complete neurologic dysfunction persisting 24 hours after injury has a very low probability of return of function in the involved area.

Neurologic injury from spine trauma may occur immediately or in delayed fashion. Immediate neurologic injury may be due to direct damage to the spinal cord or nerve roots from penetrating injuries, especially from stab wounds or gunshots. Blunt trauma may transfer sufficient force to the spine to cause acute disruption of bone and ligament and lead to subluxation, which is shift of one vertebral element in relation to the adjacent level. Subluxation decreases the size of the spinal canal and neural foramina, and causes compression of the cord or roots. Such neural impingement can also result from propulsion of bone fragments into the canal during a fracture. Transection, crush injury, and cord compression impairing perfusion are mechanisms leading to spinal cord injury. Delayed neurologic injury may occur during transportation or examination of a patient who is not properly immobilized.

The Mechanics of Spine Trauma

Trauma causes a wide variety of injury patterns in the spine due to its biomechanic complexity. A mechanistic approach facilitates an understanding of the patterns of injury, as there are only a few types of forces that can be applied to the spine. Although these forces are discussed individually, they often occur in combination. Several of the most common injury patterns are then presented to illustrate the clinical results of these forces and combinations of forces applied at pathologically high levels.

Flexion/Extension. Bending the head and body forward into a fetal position flexes the spine. Flexion loads the spine anteriorly (the vertebral bodies) and distracts the spine posteriorly (the spinous process and interspinous ligaments). High flexion forces occur during front-end motor vehicle collisions, and backward falls when the head strikes first. Arching the neck and back extends the spine. Extension loads the spine posteriorly and distracts the spine anteriorly. High extension forces occur during rear-end motor vehicle collisions (especially if there is no headrest), frontward falls when the head strikes a first, or diving into shallow water.

Compression/Distraction. Force applied along the spinal axis (axial loading) compresses the spine. Compression loads the spine anteriorly and posteriorly. High compression forces occur when a falling object strikes the head or shoulders, or when landing on the feet, buttocks, or head after a fall from height. A pulling force in line with the spinal axis distracts the spine. Distraction unloads the spine anteriorly and posteriorly. Distraction forces occur during a hanging, when the chin or occiput strikes an object first during a fall, or when a passenger submarines under a loose seat belt during a front-end motor vehicle collision.

Rotation. Force applied tangential to the spinal axis rotates the spine. Rotation depends on the range of motion of intervertebral facet joints. High rotational forces occur during off-center impacts to the body or head or during glancing automobile accidents.

Patterns of Injury

Certain patterns of injury resulting from the forces described above or from combinations

of those forces occur commonly and should be recognized during plain film imaging of the spine. Always completely evaluate the spine. A patient with a spine injury at one level is at significant risk for additional injuries at other levels.

Cervical. The cervical spine is more mobile than the thoracolumbar spine. Stability comes primarily from the multiple ligamentous connections of adjacent vertebral levels. Disruption of the cervical ligaments can lead to instability in the absence of fracture. The mass of the head transmits significant forces to the cervical spine during abrupt acceleration or deceleration, increasing risk for injury.

Jefferson Fracture. Jefferson's fracture is a bursting fracture of the ring of C1 (the atlas) due to compression forces. There are usually two or more fractures through the ring of C1. The open-mouth odontoid view may show lateral dislocation of the lateral masses of C1. The rule of Spence states that 7 mm or greater combined dislocation indicates disruption of the transverse ligament. The transverse ligament stabilizes C1 with respect to C2. Jefferson fractures dislocated less than 7 mm are usually treated with a rigid collar, while those dislocated 7 mm or greater are usually treated with a halo vest. Surgical intervention is not indicated.

Odontoid Fractures. The odontoid process, or dens, is the large ellipse of bone arising anteriorly from C2 (the axis) and projecting up through the ring of C1 (the atlas). Several strong ligaments connect the odontoid to C1 and to the base of the skull. Odontoid fractures usually result from flexion forces. Odontoid fractures are classified as type I, II, or III. A type I fracture involves the tip only. A type II fracture passes through the base of the odontoid process. A type III fracture passes through the body of C2. Types I and II are considered unstable and should be externally immobilized by a halo vest or fused surgically. Surgery is often undertaken for widely displaced fractures (poor chance of fusing) and for those that fail external immobilization. Type III fractures usually fuse with external immobilization only.

Hangman's Fracture. Traditionally considered a hyperextension/distraction injury from placement of the noose under the angle of the jaw, hangman's fractures may also occur with hyperextension/compression, as with diving accidents, or hyperflexion. Its definition is bilateral C2 pars interarticularis fracture. The pars interarticularis is the bone between superior and inferior facet joints. The bony connection between C1 and C3 is lost. Hangman's fractures heal well with external immobilization. Surgery is indicated if there is spinal cord compression or after failure of external immobilization.

Jumped FacetsHyperflexion Injury. The facet joints of the cervical spine slope forward, and the facet from the level above can slide up and forward over the facet from the level below if the joint capsule is torn. Hyperflexion/rotation can cause a unilateral jumped facet, whereas straight hyperflexion leads to bilateral jumped facets. Patients with a unilateral injury are usually neurologically intact, while those with bilateral injury usually have spinal cord damage. The anteroposterior diameter of the spinal canal decreases more with bilateral injury, leading to spinal cord compression (Fig. 41-10).

Thoracolumbar. The thoracic spine is significantly stabilized by the rib cage. The lumbar spine has comparatively very large vertebrae. Thus the thoracolumbar spine has a higher threshold for injury than the cervical spine. The three-column model is useful for categorizing thoracolumbar injuries. The anterior longitudinal ligament and the anterior half of the vertebral body constitute the anterior column. The posterior half of the vertebral body and the posterior longitudinal ligament constitute the middle column. The pedicles, facet joints, laminae, spinous processes, and interspinous ligaments constitute the posterior column.

Compression Fracture. This is a compression/flexion injury causing failure of the anterior column only. It is stable and not associated with neurologic deficit, although the patient may still have significant pain (Fig. 41-11).

Burst Fracture. This is a pure axial compression injury causing failure of the anterior and middle columns. It is unstable, and perhaps half of patients have neurologic deficit due to compression of the cord or cauda equina from bone fragments retropulsed into the spinal canal.

Chance Fracture. This is a flexion-distraction injury causing failure of the middle and posterior columns. It is typically unstable and is often associated with neurologic deficit.

Fracture-Dislocation. This is failure of the anterior, middle, and posterior columns caused by flexion/distraction, shear, or compression forces. Neurologic deficit can result from retropulsion of middle column bone fragments into the spinal canal, or from subluxation causing decreased canal diameter (Fig. 41-12).

Initial Assessment and Management

The possibility of a spine injury must be considered in all trauma patients. A patient with no symptoms referable to neurologic injury, a normal neurologic exam, no neck or back pain, and a known mechanism of injury unlikely to cause spine injury is at minimal risk for significant injury to the spine. Victims of moderate or severe trauma, especially those with injuries to other organ systems, usually fail to meet these criteria or cannot be assessed adequately. The latter is often due to impaired sensorium or significant pain. Because of the potentially catastrophic consequences of missing occult spine instability in a neurologically intact patient, a high level of clinical suspicion should govern patient care until completion of clinical and radiographic evaluation.

The trauma patient should be kept on a hard flat board with straps and pads used for immobilization. A hard cervical collar is kept in place. These steps minimize forces transferred through the spine, and therefore decrease the chance of causing dislocation, subluxation, or neural compression during transport to the trauma bay. The patient is then moved from the board to a flat stretcher. The primary survey and resuscitation are completed. Physical exam and initial x-rays follow.

For the exam, approach the patient as described in the section on neurologic examination

earlier in this chapter. Evaluation for spine or spinal cord injury is easier and more informative in awake patients. If the patient is awake, ask if he or she recalls details of the nature of the trauma, and if there was loss of consciousness, numbness, or inability to move any or all limbs. Assess motor function by response to commands or pain, as appropriate. Assess pinprick, light touch, and joint position if possible. Determining the anatomically lowest level of intact sensation can pinpoint the level of the lesion along the spine. Test sensation in an ascending fashion, as the patient will be better able to note when he or she first feels the stimulus, rather than when he or she can no longer feel it. Document muscle stretch reflexes, lower sacral reflexes (i.e., anal wink and bulbocavernosus), and rectal tone.

American Spinal Injury Association Classification. The American Spinal Injury Association (ASIA) provides a method of classifying patients with spine injuries. The classification indicates completeness and level of the injury and the associated deficit. A form similar to that shown in Fig. 41-13 should be available in the trauma bay and completed for any spine injury patient. The association also has worked to develop recommendations and guidelines to standardize the care of SCI patients in an effort to improve the quality of care.

Neurologic Syndromes

Penetrating, compressive, or ischemic cord injury can lead to several characteristic presentations based on the anatomy of injury. The neurologic deficits may be deduced from the anatomy of the long sensory and motor tracts and understanding of their decussations (Fig. 41-14). Four patterns are discussed. First, injury to the entire cord at a given level results in anatomic or functional cord transection with total loss of motor and sensory function below the level of the lesion. The typical mechanism is severe traumatic vertebral subluxation reducing spinal canal diameter and crushing the cord. Second, injury to half the cord at a given level results in Brown-Sequard syndrome, with loss of motor control and proprioception ipsilaterally, and loss of nociception and thermoception contralaterally. The typical mechanism is a stab or gunshot wound. Third, injury to the interior of the cord results in central cord syndrome, with upper extremity worse than lower extremity weakness and varying degrees of numbness. The typical mechanism is transient compression of the cervical cord by the ligamentum flavum buckling in posteriorly during traumatic neck hyperextension. This syndrome occurs in patients with preexisting cervical stenosis. Fourth, injury to the ventral half of the cord results in anterior cord syndrome, with paralysis and loss of nociception and thermoception bilaterally. The typical mechanism is acute disc herniation or ischemia from anterior spinal artery occlusion.

Studies

Anteroposterior (AP) and lateral plain films provide a rapid survey of the bony spine. Plain films detect fractures and dislocations well. Adequate visualization of the lower cervical and upper thoracic spine is often impossible because of the shoulder girdle. Complete plain film imaging of the cervical spine includes an open-mouth odontoid view

to assess the odontoid and the lateral masses of C1. Fine-slice CT scan with sagittal and coronal reconstructions provides good detail of bone anatomy, and is good for characterizing fractures seen on plain films, as well as visualizing C7-T1 when not well seen on plain films. MRI provides the best soft tissue imaging. Canal compromise from subluxation, acute disc herniations, or ligamentous disruption is clearly seen. MRI also may detect damage to the spinal cord itself, including contusions or areas of ischemia.

Definitive Management

Spinal-Dose Steroids. The National Acute Spinal Cord Injury Study (NASCIS) I and II papers provide the basis for the common practice of administering high-dose steroids to patients with acute spinal cord injury. A 30-mg/kg IV bolus of methylprednisolone is given over 15 minutes, followed by a 5.4-mg/kg per hour infusion begun 45 minutes later. The infusion is continued for 23 hours if the bolus is given within 3 hours of injury, or for 47 hours if the bolus is given within 8 hours of injury. The papers indicate greater motor and sensory recovery at 6 weeks, 6 months, and 1 year after acute spinal cord injury in patients who received methylprednisolone.8,9 However, the NASCIS trial data have been extensively criticized, as many argue that the selection criteria and study design were flawed, making the results ambiguous. Patients who receive such a large corticosteroid dose have increased rates of medical and ICU complications, such as pneumonias, which have a deleterious affect on outcome. A clear consensus on the use of spinal-dose steroids does not exist.10 A decision to use or not use spinal-dose steroids may be dictated by local or regional practice patterns, especially given the legal liability issues surrounding spinal cord injury. Patients with gunshot injuries or nerve root (cauda equina) injury, as well as those on chronic steroid therapy, who are pregnant, or who are less than 14 years old were excluded from the NASCIS studies, and should not receive spinal-dose steroids.

Orthotic Devices. Rigid external orthotic devices can stabilize the spine by decreasing range of motion and minimizing stress transmitted through the spine. Commonly used rigid cervical orthotics include Philadelphia and Miami-J collars. Cervical collars are inadequate for C1, C2, or cervicothoracic instability. Cervicothoracic orthoses (CTOs) brace the upper thorax and the neck, improving stabilization over the cervicothoracic region. Minerva braces improve high cervical stabilization by bracing from the upper thorax to the chin and occiput. Halo-vest assemblies provide the most external cervical stabilization. Four pins driven into the skull lock the halo ring in position. Four posts arising from a tight-fitting rigid plastic vest immobilize the halo ring. Lumbar stabilization may be provided by thoracolumbosacral orthoses (TLSOs). A variety of companies manufacture lines of spinal orthotics. A physician familiar with the technique should fit a halo-vest. Assistance from a trained orthotics technician improves fitting and adjustment of the other devices.

Surgery. Neurosurgical intervention has two goals. First is the decompression of the spinal cord or nerve roots in patients with incomplete neurologic deficits. These patients should be decompressed expeditiously, especially if there is evidence of neurologic deterioration over time. Second is the stabilization of injuries judged too unstable to heal

with external orthotics only. Spine trauma patients with complete neurologic deficit, without any signs of recovery, or those without any neurologic deficits who have bony or ligamentous injury requiring open fixation, may be medically stabilized before undergoing surgery. Surgical stabilization may be indicated for some injuries that would eventually heal with conservative treatment. Surgical stabilization can allow early mobilization, aggressive nursing care, and physical therapy. Solid surgical stabilization may also allow a patient to be managed with a rigid cervical collar who would otherwise require halo-vest immobilization.

Continued Care

Regional spinal cord injury centers with nurses, respiratory therapists, pulmonologists, physical therapists, physiatrists, and neurosurgeons specifically trained in caring for these patients may improve outcomes. Frequently encountered ICU issues include hypotension and aspiration pneumonia. Chronically, prevention and treatment of deep venous thrombosis, autonomic hyperreflexia, and decubitus ulcer formation are important. Patients with high cervical cord injuries (C4 or above) will often be terminally ventilator dependent. Many patients with cervical or high thoracic cord injuries require prolonged ventilatory support until the chest wall becomes stiff enough to provide resistance for diaphragmatic breathing. Patients should be transferred to spinal cord injury rehabilitation centers after stabilization of medical and surgical issues.

Peripheral Nerve Trauma

The peripheral nervous system extends throughout the body and is subject to injury from a wide variety of traumas. Peripheral nerves transmit motor and sensory information between the CNS and the body. An individual nerve may have pure motor, pure sensory, or mixed motor and sensory functions. The key information-carrying structure of the nerve is the axon. The axon transmits information from the neuronal cell body and may measure from less than 1 mm to greater than 1 m in length. Axons that travel a significant distance are often covered with myelin, which is a lipid-rich, electrically-insulating sheath formed by Schwann cells. Myelinated axons transmit signals much more rapidly than unmyelinated axons, because the voltage shifts and currents that define action potentials effectively jump from gap to gap over the insulated lengths of the axon.

Axons, whether myelinated or unmyelinated, travel through a collagenous connective tissue known as endoneurium. Groups of axons and their endoneurium form bundles known as fascicles. Fascicles run through a tubular collagenous tissue known as perineurium. Groups of fascicles are suspended in mesoneurium. Fascicles and their mesoneurium run through another tubular collagenous tissue known as epineurium. The epineurium and its contents form the nerve.

There are four major mechanisms of injury to peripheral nerves. Nerves may be lacerated, stretched, compressed, or contused. Knives, passing bullets, or jagged bone fractures may lacerate nerves. Adjacent expanding hematomas or dislocated fractures may stretch nerves. Expanding hematomas, external orthoses such as casts or braces, or

blunt trauma over a superficial nerve may compress or crush nerves. Shock waves from high-velocity bullets may contuse nerves. These mechanisms of injury cause damage to the various anatomic components of the nerve. The patterns of damage are categorized below.

Certain nerve segments are particularly vulnerable to injury. The following four characteristics make a nerve segment more vulnerable: proximity to a joint, superficial course, passage through a confined space, and being fixed in position.

Types of Injury

The traditional classification system for peripheral nerve injury is the Seddon classification. Seddon described three injury patterns: neurapraxia, axonotmesis, and neurotmesis, as defined below. The Seddon classification provides a simple, anatomically-based approach to peripheral nerve injury.

Neurapraxia. Neurapraxia is defined as the temporary failure of nerve function without physical axonal disruption. Axon degeneration does not occur. Return of normal axonal function occurs over hours to months, often in the 2- to 4-week range.

Axonotmesis. Axonotmesis is the disruption of axons and myelin. The surrounding connective tissues, including endoneurium, are intact. The axons degenerate proximally and distally from the area of injury. Distal degeneration is known as wallerian degeneration. Axon regeneration within the connective tissue pathways can occur, leading to restoration of function. Axons regenerate at a rate of 1 mm per day. Significant functional recovery may occur for up to 18 months. Scarring at the site of injury from connective tissue reaction can form a neuroma and interfere with regeneration.

Neurotmesis. Neurotmesis is the disruption of axons and endoneurial tubes. Peripheral collagenous components, such as the epineurium, may or may not be intact. Proximal and distal axonal degeneration occurs. The likelihood of effective axonal regeneration across the site of injury depends on the extent of neuroma formation and on the degree of persisting anatomic alignment of the connective tissue structures. For instance, an injury may damage axons, myelin, and endoneurium, but leave perineurium intact. In this case the fascicle sheath is intact, and appropriate axonal regeneration is more likely to occur than if the sheath is interrupted.

Management of Peripheral Nerve Injury

The sensory and motor deficits should be accurately documented. Deficits are usually immediate. Progressive deficit suggests a process such as an expanding hematoma, and may need early surgical exploration. Clean, sharp injuries may also benefit from early exploration and reanastomosis. Most other peripheral nerve injuries should be observed. Electromyography and nerve conduction studies (EMG/NCS) should be done 3 to 4 weeks postinjury if deficits persist. Axon segments distal to the site of injury conduct action potentials normally until wallerian degeneration occurs, so EMG/NCS before 3

weeks is not informative. Continue observation if function improves. Explore the nerve surgically if no functional improvement occurs over 3 months. If intraoperative electrical testing reveals conduction across the injury, continue observation. In the absence of conduction, the segment should be resected and end-to-end primary anastomosis attempted. Anastomoses under tension will not heal, so a nerve graft may be needed to bridge the gap between the proximal and distal nerve ends. The sural nerve is often harvested, as it carries only sensory fibers and leaves a minor deficit when harvested. The connective tissue structures of the nerve graft may provide a pathway for effective axonal regrowth across the injury.

Patterns of Injury

Brachial Plexus. The brachial plexus may be injured in a variety of ways. Parturition or a motorcycle accident can lead to plexus injury due to dislocation of the glenohumeral joint. Attempting to arrest a fall with one's hands can lead to a stretch injury of the plexus due to abrupt movement of the shoulder girdle. A lung apex tumor, known as a Pancoast tumor, can cause compression injury to the plexus. There are many patterns of neurologic deficits possible with injury to the various components of the brachial plexus, and understanding them all would require extensive neuroanatomic discussion. Two well-known eponymous syndromes are Erb's palsy and Klumpke's palsy. Injury high in the plexus to the C5 and C6 roots resulting from glenohumeral dislocation causes Erb's palsy with the characteristic "bellhop's tip" position. The arm hangs at the side, internally rotated. Hand movements are not affected. Injury low in the plexus, to the C8 and T1 roots, resulting from stretch or compression injury, causes Klumpke's palsy with the characteristic "claw hand"deformity. There is weakness of the intrinsic hand muscles, similar to that seen with ulnar nerve injury.

Radial Nerve. The radial nerve courses through the axilla, and then laterally and posteriorly in the spiral groove of the humerus. Improper crutch use can cause damage to the axillary portion. The section of the nerve traversing the spiral groove can be damaged by humerus fractures or pressure from improper positioning during sleep. This classically occurs when the patient is intoxicated and is called "Saturday night palsy." The key finding is wrist drop (i.e., weakness of hand and finger extensors). Axillary (proximal) injury causes tricep weakness in addition to wrist drop.

Common Peroneal Neuropathy. The common peroneal nerve forms the lateral half of the sciatic nerve (the medial half being the tibial nerve). It receives contributions from L4, L5, S1, and S2. It emerges as a separate nerve in the popliteal fossa and wraps laterally around the fibular neck, after which it splits to form the deep peroneal nerve and the superficial peroneal nerve. The superficial, fixed location at the fibular neck makes the nerve susceptible to compression. The classic cause of traumatic peroneal neuropathy is crush injury from a car bumper striking the lateral aspect of the leg at the level of the knee. Symptoms of common peroneal neuropathy include foot drop (weakness of the tibialis anterior) and numbness over the anterolateral surface of the lower leg and dorsum of the foot. Surgical exploration of this lesion is typically unsatisfying. Rare cases may be due to compressive fibers or adhesions that may be lysed, with the possibility of return of

function.

CEREBROVASCULAR DISEASE

Introduction

Cerebrovascular disease is the most frequent cause of new rapid-onset, nontraumatic neurologic deficit. It is a far more common etiology than seizures or tumors. Vascular structures are subject to a variety of chronic pathologic processes which compromise vessel wall integrity. Diabetes, high cholesterol, high blood pressure, and smoking are risk factors for vascular disease. These conditions can lead to vascular damage by such mechanisms as atheroma deposition causing luminal stenosis, endothelial damage promoting thrombogenesis, and weakening of the vessel wall resulting in aneurysm formation or dissection. These processes may coexist. For instance, a vessel may contain an atheromatous plaque that significantly decreases lumen diameter, and also have compromised endothelium over the plaque, providing the opportunity for thrombus formation, which can lead to acute total occlusion of the remaining lumen. Aneurysms and dissection often occur in atheromatous vessels. Specific patterns of disease relevant to the cerebrovascular system are atheromatous and thrombotic carotid occlusion, brain ischemia due to embolus from a proximal source, vessel wall breakage leading to hemorrhage, and rupture of abnormal, thin-walled structures, specifically aneurysms and arteriovenous malformations.

Ischemic Diseases

Ischemic stroke accounts for approximately 85 of acute cerebrovascular events. Symptoms of acute ischemic stroke vary based on the functions of the neural tissues supplied by the occluded vessel, and the presence or absence of collateral circulation. The circle of Willis provides extensive collateral circulation, as it connects the right and left carotid arteries to each other and each to the vertebrobasilar system. Patients with complete occlusion of the carotid artery proximal to the circle of Willis may be asymptomatic if the blood flow patterns can shift and provide sufficient circulation to the ipsilateral cerebral hemisphere from the contralateral carotid and the basilar artery. However, the anatomy of the circle of Willis is highly variable. Patients may have a hypoplastic or missing communicating artery, both anterior cerebral arteries supplied by one carotid, or the posterior cerebral artery supplied by the carotid rather than the basilar. Similarly, one vertebral artery is often dominant, and the other hypoplastic. These variations may make disease in a particular vessel more neurologically devastating than in a patient with full collateral circulation. Occlusion distal to the circle of Willis generally results in stroke in the territory supplied by the particular artery.

Neurologic deficit from occlusive disease may be temporary or permanent. A patient with sudden-onset focal neurologic deficit that resolves within 24 hours has had a transient ischemic attack (TIA). If the deficit resolves between 24 hours and 1 week, then the patient has had a reversible ischemic neurologic deficit (RIND). A patient with permanent deficits has had a cerebrovascular accident (CVA). CVA is a commonly used,

but vague term. Some prefer the term completed stroke.

Thrombotic Disease

The most common area of neurologically significant vessel thrombosis is the carotid artery in the neck. Disease occurs at the carotid bifurcation. Thrombosis of a carotid artery chronically narrowed by atheroma can lead to acute carotid occlusion. As discussed above, this may or may not cause symptoms. The more common concern is thromboembolus. Intracranial arterial occlusion by local thrombus formation may occur, but is considered rare compared to embolic occlusion.

Management

Complete occlusion of the carotid artery without referable neurologic deficit requires no treatment. A patient with new neurologic deficit and an angiographically demonstrated complete carotid occlusion contralateral to the symptoms should be considered for emergency carotid endarterectomy.11 Surgery should not be performed on obtunded or comatose patients, and should be done within 2 hours of symptom onset. This time restriction significantly reduces the number of candidates.

Embolic Disease

Emboli causing strokes may originate in the left atrium due to atrial fibrillation, on a hypokinetic left ventricular wall segment, or in valvular vegetations, an atheromatous aortic arch, or stenosed carotid bifurcations, or from the systemic venous system in the presence of a right-to-left shunt, such as a patent foramen ovale. The majority of emboli enter the anterior (carotid) circulation rather than the posterior (vertebrobasilar) circulation. Characteristic clinical syndromes result from embolic occlusion of the various vessels.

Common Types of Strokes

Anterior Cerebral Artery Stroke. The ACA supplies the medial frontal and parietal lobes, including the motor strip, as it courses into the interhemispheric fissure. ACA stroke results in contralateral leg weakness.

Middle Cerebral Artery Stroke. The MCA supplies the lateral frontal and parietal lobes and the temporal lobe. MCA stroke results in contralateral face and arm weakness. Dominant-hemisphere MCA stroke causes language deficits. Proximal MCA occlusion causing ischemia and swelling in the entire MCA territory can lead to significant intracranial mass effect and midline shift (see Fig. 41-6).

Posterior Cerebral Artery Stroke. The PCA supplies the occipital lobe. PCA stroke results in a contralateral homonymous hemianopsia (see Fig. 41-6).

Posterior Inferior Cerebellar Artery Stroke. The PICA supplies the lateral medulla

and the inferior half of the cerebellar hemispheres. PICA stroke results in nausea, vomiting, nystagmus, dysphagia, ipsilateral Horner's syndrome, and ipsilateral limb ataxia. The constellation of symptoms resulting from PICA occlusion is referred to as lateral medullary syndrome or Wallenberg's syndrome.

Management

Ischemic stroke management has two goals: reopen the occluded vessel and maintain blood flow to borderline ischemic tissues on the border of the vascular territory. This bordering tissue is referred to as the ischemic penumbra. The first goal, reopening the vessel, may be attempted with recombinant tPA.12 tPA administration within 3 hours of the onset of neurologic deficit improves outcome at 3 months. Obtain a head CT immediately in the setting of suspected ischemic stroke to differentiate ischemic from hemorrhagic stroke. Intracranial hemorrhage, major surgery in the previous 2 weeks, gastrointestinal or genitourinary hemorrhage in the previous 3 weeks, platelet count 100,000/uL, and systolic blood pressure (SBP) >185 mm Hg are among the contraindications to tPA therapy. The neurology stroke team should be called while taking the patient to head CT.

Patients not eligible for tPA require hemodynamic optimization and neurologic monitoring. Admit such patients to the ICU stroke service for blood pressure management and frequent neurologic checks. Allow the blood pressure to run high to maximize cerebral perfusion. SBP more than 180 mm Hg may require treatment. Give normal saline solution without glucose (which could injure neurons in the penumbra), and aim for normovolemia. A stroke patient who worsens clinically should undergo repeat head CT to evaluate for hemorrhage or significant mass effect from swelling. Swelling typically peaks 3 to 5 days after the stroke. Significant swelling from an MCA stroke or cerebellar stroke may be life threatening and require hemicraniectomy or suboccipital craniectomy, respectively, as described in the section on neurosurgical emergencies, earlier in this chapter.

Hemorrhagic Diseases

Intracranial hemorrhage (ICH) from abnormal or diseased vascular structures accounts for approximately 15 of acute cerebrovascular events. Hypertension and amyloid angiopathy account for most intraparenchymal hemorrhages, although arteriovenous malformations (AVMs), aneurysms, venous thrombosis, tumors, hemorrhagic conversion of ischemic infarct, and fungal infections may also be the cause. The term intracranial hemorrhage is frequently used to mean intraparenchymal hemorrhage, and will be used here. ICH causes local neuronal injury and dysfunction, and can also cause global dysfunction due to mass effect if of sufficient volume. AVM or aneurysm rupture results in subarachnoid hemorrhage (SAH), because the major cerebral and cortical blood vessels travel between the pia and the arachnoid membrane, in the subarachnoid space. SAH can cause immediate concussive-like neuronal dysfunction by exposure of the brain to intra-arterial pressure pulsations during the hemorrhage, and can cause delayed ischemia from cerebral arterial vasospasm.

Patients presenting with ICHs that do not follow typical patterns should undergo angiography or MRI to evaluate for possible underlying lesions, such as AVM or tumor.

Patients who suffer a hemorrhagic stroke are more likely to present lethargic or obtunded than those who suffer an ischemic stroke. Depressed mental status results from brain shift and herniation secondary to mass effect from the hematoma. Ischemic stroke does not cause mass effect acutely, therefore patients are more likely to present with normal consciousness and a focal neurologic deficit. Hemorrhagic strokes tend to present with a relatively smooth onset of symptoms as the hematoma expands, rather than the immediately maximal symptoms caused by ischemic stroke. Table 41-3 provides a listing of relative incidences of ICH by anatomic distribution.

Hypertension

Hypertension increases the relative risk of ICH by approximately fourfold, likely due to chronic degenerative vasculopathy. Hypertensive hemorrhages often present in the basal ganglia, thalamus, or pons, and result from breakage of small perforating arteries that branch off of much larger parent vessels (Fig. 41-15).

Most hypertensive hemorrhages should be medically managed. The hematoma often contains intact, salvageable axons because the blood dissects through and along neural tracts, and surgical clot evacuation destroys these axons. Factors that indicate that surgery may be appropriate include superficial clot location, young age, nondominant hemisphere, rapid deterioration, and significant mass effect. Most studies fail to show overall improved outcomes. Medical management includes moderate blood pressure control, normalizing platelet and clotting function, phenytoin, and electrolyte management. Intubate patients who cannot clearly follow commands, to prevent aspiration and hypercarbia. Follow and document the neurologic exam and communicate with the family regarding appropriateness for rehabilitation versus withdrawal of care.

Amyloid Angiopathy

The presence of pathologic amyloid deposition in the media of small cortical vessels compromises vessel integrity, predisposes to more superficial (lobar) hemorrhages, and may cause multiple hemorrhages over time.

The superficial location of amyloid hemorrhages may make surgical evacuation less morbid than for typical deep hypertensive hemorrhages. Approach medical management and family counseling similarly to patients with hypertensive hemorrhages.

Cerebral Aneurysm

An aneurysm is focal dilatation of the vessel wall, and is most often a balloon-like outpouching, but may also be fusiform. Aneurysms usually occur at branch points of major vessels [e.g., internal carotid artery (ICA) bifurcation], or at the origin of smaller

vessels (e.g., posterior communicating artery or ophthalmic artery). Approximately 85 of aneurysms arise from the anterior circulation (carotid) and 15 from the posterior circulation (vertebrobasilar). Table 41-4 shows the percentage distribution of cerebral aneurysms by location. Aneurysms are thin-walled and at risk for rupture. The major cerebral vessels, and therefore aneurysms, lie in the subarachnoid space. Rupture results in SAH. The aneurysmal tear may be small and seal quickly or not. SAH may consist of a thin layer of blood in the CSF spaces, or thick layers of blood around the brain and extending into brain parenchyma, resulting in a clot with mass effect. The meningeal linings of the brain are sensitive, so SAH usually results in a sudden, severe "thunderclap" headache. A patient will classically describe "the worst headache of my life." Presenting neurologic symptoms may range from mild headache to coma to sudden death. The Hunt-Hess grading system categorizes patients clinically (Table 41-5).

Patients with symptoms suspicious for SAH should have a head CT immediately. Acute SAH appears as a bright signal in the fissures and CSF cisterns around the base of the brain, as shown in Fig. 41-16. CT is rapid, noninvasive, and approximately 95 sensitive. Patients with suspicious symptoms but negative head CT should undergo lumbar puncture. A lumbar puncture (LP) with xanthochromia and high red blood cell (RBC) counts (usually 100,000/mL), which do not decrease between tubes 1 and 4, is consistent with SAH. Negative CT and LP essentially rules out SAH. Patients diagnosed with SAH require four-vessel cerebral angiography within 24 hours to assess for aneurysm or other vascular malformation. Catheter angiography remains the gold standard for assessing the patient's cerebral vasculature, relevant anomalies, and presence, location, and morphology of the cerebral aneurysms. Parts A and B of Fig. 41-17 demonstrate the typical digital subtraction angiographic (DSA) view of a cerebral aneurysm. Part C shows the anatomy of the circle of Willis in a simplified graphic representation to assist in visualizing the locations of various cerebral aneurysms.

SAH patients should be admitted to the neurologic ICU. Hunt-Hess grade 4 and 5 patients require intubation and hemodynamic monitoring and stabilization. The current standard of care for ruptured aneurysms requires early aneurysmal occlusion. There are two options for occlusion. The patient may undergo craniotomy with microsurgical dissection and placement of a titanium clip across the aneurysm neck to exclude the aneurysm from the circulation and reconstitute the lumen of the parent vessel. The second option is to take the patient to the interventional neuroradiology suite for endovascular placement of looped titanium coils inside the aneurysm dome. The coils support thrombosis and prevent blood flow into the aneurysm. Factors favoring craniotomy and clipping include young age, good medical condition, and broad aneurysm necks. Factors favoring coiling include old or medically-frail patients and narrow aneurysm necks. Clipping results in a more definitive cure, because coils can move and compact over time, requiring repeat angiograms and placement of additional coils. The decision to clip or coil is complex and should be fully explored. The International Subarachnoid Aneurysm Trial (ISAT) researchers suggested that endovascular occlusion resulted in better outcomes for certain types of cerebral aneurysms, although this trial was marred by poor selection and randomization techniques, and the validity of its conclusions have been questioned.13 Debate also continues regarding optimal care for unruptured intracranial

aneurysms.14

SAH patients often require 1 to 3 weeks of ICU care after aneurysm occlusion for medical complications that accompany neurologic injury. In addition to routine ICU concerns, SAH patients are also at risk for cerebral vasospasm. In vasospasm, cerebral arteries constrict pathologically and can cause ischemia or stroke from 4 to 21 days after SAH. Current vasospasm prophylaxis includes maintaining hypertension and mild hypervolemia to optimize perfusion, and administering nimodipine, a calcium channel blocker that may decrease the incidence and degree of spasm. Neurointerventional options for treating symptomatic vasospasm are intra-arterial papaverine and balloon angioplasty.

Aneurysmal SAH has an approximate mortality rate of 50 in the first month. Approximately one-third of survivors returns to pre-SAH function, and the remaining two-thirds have mild to severe disability. Most require rehabilitation after hospitalization.

Arteriovenous Malformations

AVMs are abnormal, dilated arteries and veins without an intervening capillary bed. The nidus of the AVM contains a tangled mass of vessels, but no neural tissue. AVMs may be asymptomatic or present with SAH or seizures. Small AVMs present with hemorrhage more often than large AVMs, which tend to present with seizures. Headache, bruit, or focal neurologic deficits are less common symptoms. AVMs hemorrhage at an average rate of 2 to 4 a year. Figure 41-18 demonstrates the angiographic appearance of an AVM in arterial and venous phases.

There are several management differences for SAH due to AVM versus aneurysm. Definitive therapy for the AVM is usually delayed 3 to 4 weeks to allow the brain to recover from acute injury. There is less risk of devastating early rebleeding from AVMs, and vasospasm is less relevant. Adjacent brain may be hyperemic after removal of the high-flow arteriovenous (A-V) shunt, so hypertension and hypervolemia are not beneficial. Three therapeutic modalities for AVMs are currently in common use: microsurgical excision, endovascular glue embolization, and stereotactic radiosurgery. AVMs that are large, near eloquent cortex, or that drain to deep venous structures are considered high grade and more difficult to surgically resect without causing significant neurologic deficit. Radiosurgery can treat these lesions, although it is limited to lesions less than 3 cm in diameter and has a 2-year lag time (i.e., the AVM may bleed in the interval). Embolization reduces flow through the AVM. It is usually considered adjunctive therapy, but may rarely be the sole treatment for deep, inaccessible lesions.

TUMORS OF THE CENTRAL NERVOUS SYSTEM

Introduction

A wide variety of tumors affect the brain and spine. Primary benign and malignant

tumors arise from the various elements of the CNS, including neurons, glia, and meninges. Tumors metastasize to the CNS from many primary sources. Presentation varies widely depending on relevant neuroanatomy. Prognosis depends on histology and anatomy. Modern brain tumor centers utilize team approaches to CNS tumors, as patients may require a combination of surgery, radiation therapy, chemotherapy, stereotactic radiosurgery, and research protocol enrollment. Tumors affecting the peripheral nervous system are discussed in the peripheral nerve section.

Intracranial Tumors

Intracranial tumors are brain tumors that cause mass effect, dysfunction or destruction of adjacent neural structures, swelling, abnormal electrical activity, or a combination of these. Supratentorial tumors commonly present with focal neurologic deficit, such as contralateral limb weakness or visual field deficit, or headache or seizure. Infratentorial tumors often cause increased ICP, due to hydrocephalus due to compression of the fourth ventricle, leading to headache, nausea, vomiting, or diplopia. Cerebellar hemisphere or brain stem dysfunction can lead to ataxia, nystagmus, or cranial nerve palsies. Infratentorial tumors rarely cause seizures.

All patients with symptoms concerning for brain tumor should undergo MRI with and without gadolinium. Initial management of a patient with a symptomatic brain tumor generally includes dexamethasone (if edema is present) and phenytoin (supratentorial tumors only). Patients with significant weakness, lethargy, or hydrocephalus should be admitted for observation until definitive care is administered.

Metastatic Tumors

Prolonged cancer patient survival and improved CNS imaging have increased the likelihood of diagnosing cerebral metastases. The sources of most cerebral metastases are (in decreasing frequency) the lung, breast, kidney, GI tract, and melanoma. Lung and breast cancers account for more than half of cerebral metastases. Metastatic cells usually travel to the brain hematogenously and frequently seed the gray-white junction. Other common locations are the cerebellum and the meninges. The latter leads to carcinomatous meningitis, also known as leptomeningeal carcinomatosis. MRI pre- and post-contrast administration is the study of choice for evaluation. Figure 41-19 demonstrates bilateral cerebellar metastases. Metastases are often very well circumscribed, round, and multiple. Such findings should instigate a metastatic work-up, including CT scan of the chest, abdomen, and pelvis, and a bone scan.

Management depends on the primary tumor, tumor burden, patient's medical condition, and location and number of metastases. The patient's and family's beliefs regarding aggressive care must be considered. Craniotomy may benefit patients with one or two accessible metastases and should be discussed. Studies do not support craniotomy unless all detectable metastases can be resected. Surgery should be followed by whole brain radiation therapy. Surgery plus radiation therapy increases average survival from 1 month to 8 months. Recent data suggest stereotactic radiosurgery (e.g., gamma knife) may be

applied to multiple metastases in one session with improved outcome.

Glial Tumors

Glial cells provide the anatomic and physiologic support for neurons and their processes in the brain. The several types of glial cells give rise to distinct primary CNS neoplasms.

Astrocytomas

Astrocytoma is the most common primary CNS neoplasm. The term glioma is often used to refer to astrocytomas specifically, excluding other glial tumors. Astrocytomas are graded from I to IV. Grades I and II are referred to as low-grade astrocytoma, grade III as anaplastic astrocytoma, and grade IV as glioblastoma multiforme (GBM). Prognosis varies significantly between grades I/II, III, and IV, but not between I and II. Median survival is 8 years after diagnosis with a low-grade tumor, 2 to 3 years with an anaplastic astrocytoma, and roughly 1 year with a GBM. GBMs account for almost two-thirds of all astrocytomas, anaplastic astrocytomas account for two-thirds of the rest, and low-grade astrocytomas the remainder. Figure 41-20 demonstrates the typical appearance of a GBM.

The great majority of astrocytomas infiltrate adjacent brain. Juvenile pilocytic astrocytomas and pleomorphic xanthoastrocytoma are exceptions. These are circumscribed, low grade, and associated with good prognosis. Histologic features associated with higher grade include hypercellularity, nuclear atypia, and endovascular hyperplasia. Necrosis is present only with GBMs; it is required for the diagnosis.

Gross total resection should be attempted for suspected astrocytomas. Motor cortex, language centers, deep or midline structures, or brain stem location may make this impossible without unacceptable, devastating neurologic deficit. These may require stereotactic needle biopsy. Gross total resection followed by radiation therapy improves survival for all grades, although radiation therapy may be delayed until recurrence in low-grade tumors. Chemotherapy may be considered, but is of limited efficacy so far. There are various ongoing research studies for GBM adjuvant therapy; these should be discussed with the patient and family. Other options are carmustine-containing wafers for local chemotherapy (Gliadel) and Iotrex-containing balloons for conformal radiation brachytherapy (Glia-Site), both placed in the resection cavity at the time of surgery. Adjuvant therapy remains marginally effective; survival has changed little over the last several decades.

Oligodendroglioma

Oligodendroglioma accounts for approximately 10 of gliomas. They often present with seizures. Calcifications and hemorrhage on CT or MRI suggest the diagnosis. Oligodendrogliomas are also graded from I to IV; grade portends prognosis. Prognosis is better overall than for astrocytomas. Median survival ranges from 2 to 7 years for highest and lowest grade tumors, respectively. Aggressive resection improves survival. Many

oligodendrogliomas will respond to procarbazine, lomustine (CCNU), vincristine (PCV) chemotherapy. Radiation has not been clearly shown to prolong survival.

Ependymoma

The lining of the ventricular system consists of cuboidal/ columnar ependymal cells from which ependymomas may arise. Two-thirds of adult ependymomas are infratentorial, while most pediatric ependymomas are supratentorial. Supratentorial ependymomas arise from the lateral or third ventricles. The infratentorial tumors arise from the floor of the fourth ventricle (i.e., off the back of the brain stem). The most common symptoms are headache, nausea, vomiting, or vertigo, secondary to increased ICP from obstruction of CSF flow through the fourth ventricle. The tumors may grow out the foramina of Luschka to form a cerebellopontine angle (CPA) mass, or may spread through the CSF to form "drop mets" in the spinal cord. Two main histologic subtypes are papillary ependymomas and anaplastic ependymomas, the latter characterized by increased mitotic activity and areas of necrosis. Gross total resection is often impossible because the tumor arises from the brain stem. The goal of surgery is maximal resection without injuring the very delicate brain stem. Suboccipital craniotomy and midline separation of the cerebellar hemispheres allows access to tumors in the fourth ventricle. Postoperative radiation therapy significantly improves survival. Patients with CSF spread documented by lumbar puncture or contrast MRI should also have whole-spine radiation plus focused doses to visualized metastases.

Choroid Plexus Papilloma

The choroid plexus is composed of many small vascular tufts covered with cuboidal epithelium. It represents part of the interface between blood and brain. The choroid cells create CSF from blood and release it into the ventricular system. Choroid plexus papillomas and choroid plexus carcinomas (rare, mostly pediatric) may arise from these cells. Papillomas usually occur in infants (usually supratentorial in the lateral ventricle), but also occur in adults (usually infratentorial in the fourth ventricle). Papillomas are well circumscribed and vividly enhance due to extensive vasculature. Like ependymomas, adult choroid plexus papillomas usually present with symptoms of increased ICP. Treatment is surgical excision. Total surgical excision is curative; recurrent papillomas should be re-resected. Do not use radiation or chemotherapy for papillomas. Radiation is adjunctive to aggressive surgery for carcinomas, but results are poor regardless.

Neural Tumors and Mixed Tumors

Neural and mixed tumors are a diverse group that includes tumors variously containing normal or abnormal neurons and/or normal or abnormal glial cells. Primitive neuroectodermal tumors (PNETs) arise from bipotential cells, capable of differentiating into neurons or glial cells.

Medulloblastoma

PNETs are the most common medulloblastomas. Most occur in the first decade of life, but there is a second peak around age 30. Medulloblastoma is the most common malignant pediatric brain tumor. They are usually midline. Most occur in the cerebellum and present with symptoms of increased ICP. Histologic characteristics include densely packed small round cells with large nuclei and scant cytoplasm. They are generally not encapsulated, frequently disseminate within the CNS, and should undergo surgical resection followed by radiation therapy and chemotherapy.

Ganglioglioma

Ganglioglioma is a mixed tumor in which both neurons and glial cells are neoplastic. They occur in the first three decades of life, often in the medial temporal lobe, as circumscribed masses that may contain cysts or calcium and may enhance. The presenting symptom is usually a seizure, due to the medial temporal location. Patients have a good prognosis after complete surgical resection.

Neural Crest Tumors

Multipotent neural crest cells develop into a variety of disparate cell types, including smooth muscle cells, sympathetic and parasympathetic neurons, melanocytes, Schwann cells, and arachnoid cap cells. They migrate in early development from the primitive neural tube throughout the body.

Miscellaneous Tumors

Meningioma

Meningiomas are derived from arachnoid cap cells of the arachnoid mater. They appear to arise from the dura mater grossly and on MRI, and so are commonly referred to as dural-based tumors. The most common intracranial locations are along the falx (Fig. 41-21), the convexities (i.e., over the cerebral hemispheres), and the sphenoid wing. Less common locations include the foramen magnum, olfactory groove, and inside the lateral ventricle. Most are slow growing, encapsulated, benign tumors. Aggressive atypical or malignant meningiomas may invade adjacent bone or into the cortex. Previous cranial irradiation increases the incidence of meningiomas. Approximately 10 of patients with a meningioma have multiple meningiomas. Total resection is curative, although involvement with small perforating arteries or cranial nerves may make total resection of skull base tumors impossible without significant neurologic deficit. Small, asymptomatic meningiomas can be followed until symptomatic or significant growth is documented on serial imaging studies. Atypical and malignant meningiomas may require postoperative radiation. Patients may develop recurrences from the surgical bed or distant de novo tumors.

Vestibular Schwannoma (Acoustic Neuroma)

Vestibular schwannomas arise from the superior half of the vestibular portion of the

vestibulocochlear nerve (cranial nerve VIII) (Fig. 41-22). They most commonly present with progressive hearing loss, tinnitus, or balance difficulty. Large tumors may cause brain stem compression and obstructive hydrocephalus. Bilateral acoustic neuromas are pathognomonic for neurofibromatosis type 2, a syndrome resulting from chromosome 22 mutation. NF-2 patients have an increased incidence of spinal and cranial meningiomas and gliomas.

Vestibular schwannomas may be treated with microsurgical resection or with conformal stereotactic radiosurgery (gamma knife or linear accelerator technology). The main complication with treatment is damage to the facial nerve (cranial nerve VII), which runs through the internal auditory canal with the vestibulocochlear nerve. Risk of facial nerve dysfunction increases with increasing tumor diameter.

Pituitary Adenoma

Pituitary ademomas arise from the anterior pituitary gland (the adenohypophysis). Tumors less than 1 cm diameter are microadenomas; larger tumors are macroadenomas. Pituitary tumors may be functional (i.e., secrete endocrinologically active compounds at pathologic levels) or nonfunctional (i.e., secrete nothing or inactive compounds). Functional tumors are often diagnosed when quite small, due to endocrine dysfunction. The most common endocrine syndromes are Cushing's disease due to adrenocorticotropic hormone (ACTH) secretion, Forbes-Albright syndrome due to prolactin secretion, and acromegaly due to growth hormone secretion. Nonfunctional tumors commonly present when larger due to mass effect. Figure 41-23 demonstrates a large pituitary adenoma. Common symptoms include visual field deficits due to compression of the optic chiasm, or panhypopituitarism due to compression of the gland. Hemorrhage into a pituitary tumor causes abrupt symptoms of headache, visual disturbance, decreased mental status, and endocrine dysfunction. This is known as pituitary apoplexy. Pituitary tumors should be decompressed surgically to eliminate symptomatic mass effect and/or to attempt endocrine cure. Prolactinomas usually shrink with dopaminergic therapy. Consider surgery for prolactinomas with persistent mass effect or endocrinologic dysfunction in spite of adequate dopamine agonist therapy. Most pituitary tumors are approached through the nose by the transsphenoidal approach. Endoscopic sinus surgery techniques may be helpful and are increasingly being used.

Hemangioblastoma

Hemangioblastomas occur almost exclusively in the posterior fossa. Twenty percent occur in patients with von Hippel-Lindau (VHL) disease, a multisystem neoplastic disorder. Other tumors associated with VHL are renal cell carcinoma, pheochromocytoma, and retinal angiomas. Many appear as cystic tumors with an enhancing tumor on the cyst wall known as the mural nodule. Surgical resection is curative for sporadic (non-VHL associated) tumors. Pathology reveals abundant thin-walled vascular channels, so internal debulking may be bloody. En bloc resection of the mural nodule alone, leaving the cyst wall, is sufficient.

Lymphoma

CNS lymphoma may arise primarily in the CNS or secondary to systemic disease. Recent increasing incidence may be due to increasing numbers of immunocompromised people in the transplant and AIDS populations. Presenting symptoms include mental status changes, headache due to increased ICP, and cranial nerve palsy due to lymphomatous meningitis (analogous to carcinomatous meningitis). Many are hyperdense on CT scan due to their dense cellularity, and most enhance. Surgical excision has little role. Diagnosis is often made by stereotactic needle biopsy. Subsequent treatment includes steroids, whole brain radiation, and chemotherapy. Intrathecal methotrexate chemotherapy is an option.

Embryologic Tumors

Embryologic tumors result from embryonal remnants that fail to involute completely or differentiate properly during development.

Craniopharyngioma

Craniopharyngiomas are benign cystic lesions that occur most frequently in children. There is a second peak of occurrence around 50 years of age. All pediatric, and half of adult craniopharyngiomas calcify. Symptoms result from compression of adjacent structures, especially the optic chiasm. Pituitary or hypothalamic dysfunction or hydrocephalus may develop. Treatment is primarily surgical. Excision is easier in children, as the tumor is usually soft and suckable. Adult tumors are often firm and adherent to adjacent vital structures. Visual loss, pituitary endocrine hypofunction, diabetes insipidus, and cognitive impairment from basal frontal injury may result from incautious resection.

Epidermoid

These are cystic lesions with stratified squamous epithelial walls from trapped ectodermal cell rests that grow slowly and linearly by desquamation into the cyst cavity. The cysts contain keratin, cholesterol, and cellular debris (Fig. 41-24). They occur most frequently in the cerebellopontine angle and may cause symptoms due to brain stem compression. Recurrent bouts of aseptic meningitis may occur due to release of irritating cyst contents into the subarachnoid space (Mollaret's meningitis). Treatment is surgical drainage and removal of cyst wall. Intraoperative spillage of cyst contents leads to severe chemical meningitis and must be avoided by containment and aspiration.

Dermoid

Dermoids are less common than epidermoids. They contain hair follicles and sebaceous glands in addition to a squamous epithelium. Dermoids are more commonly midline structures and are associated with other anomalies than are epidermoids. They may be traumatic, as from a lumbar puncture that drags skin structures into the CNS. Bacterial

meningitis may occur when associated with a dermal sinus tract to the skin. Treatment of symptomatic lesions is surgical resection, again with care to control cyst contents.

Teratoma

Teratomas are germ cell tumors that arise in the midline, often in the pineal region (the area behind the third ventricle, above the midbrain and cerebellum). They contain elements from all three embryonal layers: ectoderm, mesoderm, and endoderm. Teratomas may contain skin, cartilage, GI glands, and teeth. Teratomas with more primitive features are more malignant, while those with more differentiated tissues are more benign. Surgical excision may be attempted. Prognosis for malignant teratoma is very poor.

Spinal Tumors

A wide variety of tumors affect the spine. Approximately 20 of CNS tumors occur in the spine. The majority of spinal tumors are histologically benign, unlike cranial tumors. Understanding the two major spinal concepts facilitates understanding of the effects of spinal tumors. The two concepts are spinal stability and neural compression. Destruction of bones or ligaments can cause spinal instability, and lead to deformities such as kyphosis or subluxation and possible subsequent neural compression. Tumor growth in the spinal canal or neural foramina can cause direct compression of the spinal cord or nerve roots and cause loss of function. Anatomic categorization provides the most logical approach to these tumors. The various tumors present in characteristic locations. An understanding of the anatomy leads to an understanding of the clinical presentation and possible therapeutic options.

Extradural Tumors

Extradural tumors comprise 55 of spinal tumors. This category includes tumors arising within the bony structures of the vertebrae and in the epidural space. Destruction of the bone can lead to instability and fractures, leading to pain and/or deformity. Epidural expansion can lead to spinal cord or nerve root compression with radiculopathy or myelopathy, respectively.

Metastatic Tumors. Metastatic tumors are the most common extradural tumors. Spinal metastases most commonly occur in the thoracic and lumbar vertebral bodies because the greatest volume of red bone marrow is found therein. The most common primary tumors are lymphoma, lung, breast, and prostate. Other sources include renal, colon, thyroid, sarcoma, and melanoma. Most spinal metastases create osteolytic lesions. Osteoblastic, sclerotic lesions suggest prostate cancer in men and breast cancer in women. Patients with progressing neurologic dysfunction or debilitating pain should undergo urgent surgery or radiation therapy. Preoperative neurologic function correlates with postoperative function. Patients may lose function over hours. These patients should be given high-dose intravenous dexamethasone, taken immediately to MRI, and then to the operating room or radiation therapy suite. Indications for surgery include failure of

radiation therapy, spinal instability, recurrence after radiation therapy, and the need for diagnosis in cases of unknown primary tumors. Most cases with significant bone involvement require both decompression and fusion. Bony fusion usually takes 2 to 3 months. Prognosis governs operative decisions. Surgery is unlikely to improve quality of life for patients with a life expectancy of 3 months or less, but is likely to improve quality of life for patients with life expectancy of 6 months or more. Benefit for patients with 3 to 6 months life expectancy is unclear and requires frank discussion with the patient and family. Patients who are unlikely to tolerate general anesthesia, are already completely paralyzed, or who have very radiosensitive tumors such as myeloma and lymphoma, should generally not be offered surgery.

Primary Tumors. Hemangiomas are benign tumors found in 10 of people at autopsy. They occur in the vertebral bodies of the thoracolumbar spine and are frequently asymptomatic. They are often vascular and may hemorrhage, causing pain or neurologic deficit. Large hemangiomas can destabilize the body and predispose to fracture. Osteoblastic lesions include osteoid osteoma and osteoblastoma. The latter tends to be larger and more destructive. Aneurysmal bone cysts are nonneoplastic, expansile, lytic lesions containing thin-walled blood cavities which usually occur in the lamina or spinous processes of the cervicothoracic spine. They may cause pain or sufficiently weaken the bone to lead to fracture. Cancers arising primarily in the bony spine include Ewing's sarcoma, osteosarcoma, chondrosarcoma, and plasmacytoma.

Intradural Extramedullary Tumors

Intradural extramedullary tumors comprise 40 of spinal tumors and arise from the meninges or nerve root elements. They may compress the spinal cord, causing myelopathy, or the nerve roots, causing radiculopathy. All of the most common intradural extramedullary tumors are typically benign, slow growing, and well circumscribed. Rare benign epidural masses include arachnoid cysts, dermoids, and epidermoids. Rare malignant epidural tumors include metastases and high-grade gliomas.

Meningioma. Meningiomas arise from the arachnoid mater. They appear to be dural based and enhance on MRI. An enhancing "dural tail" may be seen. They occur most commonly in the thoracic spine (Fig. 41-25), but also arise in the cervical and lumbar regions. Some spinal meningiomas grow into the epidural space. Growth causes cord compression and progressive myelopathy with hyperreflexia, spasticity, and gait difficulties. Surgical excision is the treatment of choice. The surgeon often finds a clean margin between the tumor and dura, and between the tumor and spinal cord, allowing en bloc resection without damage to the cord.

Schwannoma. Schwannomas are derived from peripheral nerve sheath Schwann cells. They are benign, encapsulated tumors that almost never undergo malignant degeneration. Two-thirds are entirely intradural, one-sixth are entirely extradural, and one-sixth have the classic dumbbell shape from intradural and extradural components. Symptoms result from radiculopathy, often presenting as pain, or myelopathy. Symptomatic lesions should be surgically resected. The parent nerve root can usually be preserved. Patients with

multiple schwannomas likely have neurofibromatosis type 2 (NF-2). Resect symptomatic lesions in NF-2 patients.

Neurofibroma. Neurofibromas tend to be more fusiform and grow within the parent nerve, rather than forming an encapsulated mass off the nerve, as with schwannomas. They are benign but not encapsulated. They present similarly to schwannomas and the two may be difficult to differentiate on imaging. Salvage of the parent nerve is more challenging with neurofibromas. Thoracic and high cervical nerve roots may be sacrificed with minimal deficit, to improve likelihood of total resection. Patients with multiple neurofibromas likely have neurofibromatosis type 1, also known as von Recklinghausen's neurofibromatosis. Resection for symptomatic lesions should be offered.

Intramedullary Tumors

Intramedullary tumors comprise 5 of spinal tumors. They arise within the parenchyma of the spinal cord. Common presenting symptoms are local or radicular pain, sensory loss, weakness, or sphincter dysfunction. Patients with such symptoms should undergo MRI of the entire spine with and without enhancement.

Ependymoma. Ependymomas are the most common intramedullary tumors in adults. There are several histologic variants. The myxopapillary type occurs in the conus medullaris or the filum terminale in the lumbar region and has the best prognosis after resection. The cellular type occurs more frequently in the cervical cord. Many spinal ependymomas have cystic areas and may contain hemorrhage. Surgical removal can improve function. A distinct tumor margin often exists, allowing safer excision. Postoperative radiation therapy after subtotal resection may prolong disease control.

Astrocytoma. Astrocytomas are the most common intramedullary tumors in children, although they also occur in adults. They may occur at all levels, although more often in the cervical cord. The tumor may interfere with the CSF-containing central canal of the spinal cord, leading to a dilated central canal, referred to as syringomyelia, or simply syrinx. Spinal astrocytomas are usually low grade, but complete excision is rarely possible due to the nonencapsulated, infiltrative nature of the tumor. As such, patients with astrocytomas fare worse overall than patients with ependymomas.

Other Tumors. Other types of rare tumors include high-grade astrocytomas, dermoids, epidermoids, teratomas, hemangiomas, hemangioblastomas, and metastases. Patients usually present with pain. Prognosis depends generally on preoperative function and the histologic characteristics of the lesion.

SPINE

Introduction

The spine is a complex structure subject to a wide variety of pathologic processes, including degeneration, inflammation, infection, neoplasia, and trauma. Please refer to

the sections on trauma, tumor, and infection for discussions of how these processes impact the spine. General concepts relevant to the spine, as well as some common patterns of disease and operative interventions, are presented.

The spine consists of a series of stacked vertebrae, intervening discs, and longitudinal ligaments. The vertebrae consist of the vertebral body anteriorly and the pedicles, articular facets, laminae, and spinous processes posteriorly. The intervertebral discs have two components. The tough, fibrous ring that runs around the outer diameter of the two adjacent vertebral bodies is known as the annulus fibrosus. The spongy material inside the ring of the annulus is known as the nucleus pulposus. The annulus and the nucleus provide a cushion between adjacent vertebral bodies, absorb forces transmitted to the spine, and allow some movement between the vertebral bodies. The ligaments stabilize the spine by limiting the motion of adjacent vertebrae.

Two concepts critical to understanding the mechanics and pathologic processes affecting the spine are stability and neural compres sion.

Stability

The spinal column is the principal structural component of the axial spine, and it must bear significant loads. The vertebrae increase in size from the top to the bottom of the spine, correlating with the increased total loads the more caudal elements of the spine must bear. The cervical spine is the most mobile. Cervical stability depends greatly on the integrity of the ligaments that run from level to level. The thoracic spine is the least mobile, due to the stabilizing effect of the rib cage. The lumbar spine has relatively massive vertebrae, supports heavy loads, and has intermediate mobility. The sacral spine is fused together and has no intrinsic mobility. The load borne by the lumbar spine is transmitted to the sacrum, and then the pelvis through the sacroiliac joints. The coccyx is the inferiormost segment of the spine and has no significant contribution to load bearing or to mobility.

A stable spine is one that can bear normally experienced forces resulting from body mass, movement, and muscle contraction, while maintaining normal structure and alignment. An unstable spine will shift or sublux under these forces. The determinants of spinal stability vary throughout the cervical, thoracic, and lumbar portions. In elementary form, stability depends on the structural integrity of the hard, bony elements of the vertebral column, as well as the tensile integrity and secure attachments of the supporting ligamentous structures. Plain x-rays and CT scans have good sensitivity for detecting bony defects such as fractures or subluxation. MRI better detects disruption of the soft tissues, including ligaments and intervertebral discs. Specific patterns of abnormalities seen on imaging studies may lead to a diagnosis of, or high suspicion of, spinal instability.

A common form of nontraumatic spinal instability is lumbar spondylolisthesis (i.e., forward slippage of a lumbar vertebra with relation to the next lower vertebra on which it rests). This results from congenital or degenerative disruption of the pars interarticularis,

the critical bridge of bone that spans adjacent facet joints. In the setting of a so-called pars defect, there is no solid bony connection between the adjacent vertebrae. This makes the spine unstable and can lead to slippage. Patients typically present with severe low back pain that is exacerbated with movement and load bearing (mechanical low back pain). Figure 41-26 demonstrates an L4 and L5 spondylolisthesis.

Neural Compression

Besides providing a stable central element of the body's support structure, the spine must also protect the spinal cord as it descends in the central canal, and the nerve roots as they pass from the central canal out the neural foramina to form the peripheral nervous system. In a healthy spine, the spinal cord and nerve roots are suspended in CSF, free of mechanical compression. Pathologic processes that can lead to impingement on the CSF spaces and neural compression include hypertrophic degenerative changes in the intervertebral discs and facet joints, expanding epidural masses such as tumors or abscesses, and slippage of adjacent vertebral bodies with respect to each other (i.e., subluxation). Subluxation may be due to trauma that exceeds the spine's load-bearing capabilities and leads to structural failure, or chronic structural degradation by degenerative disease, infection, or tumor. Subluxation reduces the cross-sectional area of the central canal and the neural foramina (see Fig. 41-10B). Reduced central canal area can lead to myelopathy. Reduced neural foraminal area can lead to radiculopathy.

Myelopathy

Compression of the spinal cord causes disturbance of cord function, known as myelopathy. Myelopathy may be secondary to the direct effects of compression, cord ischemia due to reduced perfusion, or pathologic changes due to repeated cord trauma. These mechanisms lead to demyelination of the corticospinal tracts, which are long descending motor tracts. Corticospinal tract damage leads to upper motor neuron signs and symptoms, including hyperreflexia, spasticity, and weakness. These mechanisms also cause damage to the dorsal columns, which carry ascending proprioception, vibration, and two-point discrimination information. Loss of proprioception makes fine motor tasks and ambulation difficult.

Radiculopathy

Compression of the nerve roots causes disturbance of root function, known as radiculopathy. Characteristic features of radiculopathy include lower motor neuron signs and symptoms (hyporeflexia, atrophy, and weakness) and sensory disturbances such as numbness, tingling sensations (paresthesias), burning sensations (dysesthesias), and shooting pain. Myelopathy and radiculopathy often present together in diseases that involve the central canal and the neural foramina. This can lead to lower motor neuron dysfunction at the level of disease, and upper motor neuron dysfunction below that level.

Patterns of Disease

Cervical Radiculopathy

The cervical nerve roots exit the central canal above the pedicle of the same-numbered vertebra and at the level of the higher adjacent intervertebral disc. So, for example, the C6 nerve root passes above the C6 pedicle at the level of the C5-C6 discs. The cervical nerve roots may be compressed acutely by disc herniation, or chronically by hypertrophic degenerative changes of the discs, facets, and ligaments. Table 41-6 summarizes the effects of various disc herniations. Most patients with acute disc herniations will improve without surgery. Nonsteroidal anti-inflammatory drugs or cervical traction may help alleviate symptoms. Patients whose symptoms do not resolve or who have significant weakness should undergo decompressive surgery. The two main options for nerve root decompression are anterior cervical discectomy and fusion (ACDF) and posterior cervical foraminotomy (keyhole foraminotomy). ACDF allows more direct access to and removal of the pathology (anterior to the nerve root), but requires fusion. Figure 41-27 demonstrates a C6-C7 ACDF. Keyhole foraminotomy allows decompression without requiring fusion, but may be less effective for removing the pathology.

Cervical Spondylotic Myelopathy

The term spondylosis refers to diffuse degenerative and hypertrophic changes of the discs, intervertebral joints, and ligaments, that cause spinal stenosis. Spinal cord dysfunction (myelopathy) due to cord compression from cervical spinal degenerative disease is therefore referred to as cervical spondylotic myelopathy, or CSM. CSM classically presents with spasticity and hyperreflexia due to corticospinal tract dysfunction, upper extremity weakness and atrophy from degeneration of the motor neurons in the anterior horns of the spinal gray matter, and loss of lower extremity proprioception due to dorsal column injury. Figure 41-28 demonstrates typical findings. Patients complain of difficulty buttoning shirts, using utensils, and ambulating. Spondylosis is usually diffuse, so the usual treatment for CSM is multilevel (usually C3-C7) cervical laminectomy, although patients with disease localized over one to three levels may be candidates for anterior decompression and fusion. Figure 41-29 demonstrates the postoperative appearance of a vertebral corpectomy and fusion for CSM. Thorough cervical laminectomy decompresses the cord posteriorly. Patients often have slow recovery due to the extensive chronic changes in the cervical cord, and may benefit from rehabilitation programs. The other disease that classically presents with combined upper and lower motor neuron symptoms is amyotrophic lateral sclerosis (ALS). Care must be taken to avoid offering cervical laminectomy to a patient with undiagnosed ALS. Two findings help differentiate CSM from ALS: cranial nerve dysfunction such as dysphagia (never caused by cervical spine disease) and sensory disturbance (not found in ALS).

Thoracic Disc Herniation

Thoracic disc herniation accounts for less than 1 of herniated discs. They may present with radicular pain or sensory or motor changes in the lower extremities, due to cord compression. A posterior approach via midline incision and laminectomy should be

avoided because of the high incidence of cord injury from manipulation and retraction. Anterior approaches via thoracotomy minimize risk to the cord and allow excellent access to the disc. The radicular arteries running from the aorta to the thoracic cord should be spared when possible, to avoid ischemia.

Lumbar Radiculopathy

Lumbar nerve roots exit the thecal sac, pass over the higher adjacent disc space, and exit the canal under the pedicle of the same-numbered vertebra. Therefore, the L5 nerve root passes over the L4-L5 disc space and exits under the L5 pedicle (Fig. 41-30). Lumbar discs may herniate with or without a history of trauma or straining. They normally cause pain lancing down the leg (Table 41-7). Most acute herniated lumbar discs improve symptomatically without surgery. Surgery is indicated for symptoms persisting more than 6 to 8 weeks, progressive motor deficit (e.g., foot drop), or for patients with incapacitating pain not manageable with analgesics. Discectomy is performed using a midline incision, partial removal of the overlying laminae (hemilaminectomy or laminotomy), identification of the thecal sac and nerve root, and extraction of disc fragments. Free-floating disc fragments may be found. Often, however, the herniated disc material is still contained within the annulus, and so the annulus must be incised and the disc space curetted. After lumbar discectomy, approximately two-thirds of patients will have complete relief of pain, and up to 85 will have significant improvement.

Neurogenic Claudication

Neurogenic claudication is characterized by low back and leg pain that occurs while walking and is relieved by stopping, leaning forward, or sitting. It is normally caused by degenerative lumbar stenosis causing compression of the cauda equina. Neurogenic claudication must be distinguished from vascular claudication. Vascular claudication pain tends to resolve quickly with cessation of walking without need to change position, be in a stocking distribution rather than a dermatomal distribution, and be associated with cold, pale feet. Patients typically have a normal neurologic exam. Patients with neurogenic claudication have a slowly progressive course and may be surgical candidates when their pain interferes with their lifestyle. The usual surgery is an L3 to L5 lumbar laminectomy to decompress the nerve roots.

Cauda Equina Syndrome

Cauda equina syndrome is due to compression of the cauda equina and may result from massive disc herniation, epidural hematoma, epidural abscess, tumor, or subluxation from trauma. Patients with cauda equina compression often present with urinary retention, saddle anesthesia, or progressing leg weakness. Saddle anesthesia is numbness in the perineum, genitals, buttocks, and upper inner thighs. Patients with suspected cauda equina syndrome should undergo immediate MRI of the lumbar spine to evaluate for a surgical lesion. Mass lesions should be removed urgently via laminectomy to preserve sphincter function and ambulation.

Spine Fusion Surgery

Patients whose spines have been destabilized by disease or by surgical intervention require fusion to restore stability. Fusion procedures lock adjacent vertebrae together. Fusion occurs when the body forms a solid mass of bone incorporating the adjacent vertebrae, eliminating normal intervertebral movement. Stabilization and immobilization promote bony fusion. Internal instrumentation and external orthoses are often used to stabilize and immobilize the spinal segment being fused.

Spinal Instrumentation

Internal fixation devices for spinal segmental immobilization have been developed for all levels of the spine. Most spinal instrumentation constructs have two elements. The first element is a device that solidly attaches to the vertebral bodies. Options include wires wrapped around laminae or spinous processes, hooks placed under the lamina or around the pedicles, or screws placed in the pedicles or the vertebral bodies. The second element is a device that traverses vertebral segments. Options include rods and plates that lock directly to the wires, hooks, or screws at each vertebral level. Spinal instrumentation devices are available for anterior and posterior fusion in the cervical, thoracic, and lumbar regions. Most modern spinal instrumentation devices are made of titanium to minimize problems with future MRI scanning (Fig. 41-31). All spinal instrumentation constructs will eventually fail by loosening or breaking if bony fusion does not occur.

Arthrodesis

Arthrodesis refers to the obliteration of motion or instability by incorporating the relevant components into a solid mass of bone. Arthrodesis must occur in any fused segment to have long-term stability. Failure of arthrodesis results in failed fusion, often in the form of a fibrous nonunion. The rates of successful fusion are higher in the cervical spine than the lumbar spine. Arthrodesis requires ingrowth of new bone formed by the patient's osteoblasts across the unstable defect. Inserting graft material, such as autograft or allograft, into the defect provides a bridge for osteoblasts and promotes fusion. The term autograft refers to the patient's own bone, often harvested from the iliac crest. Iliac crest bone graft is a source of both cortical and cancellous bone. Cortical bone provides structural support, while cancellous bone provides a matrix for bony ingrowth. The term allograft refers to sterilized bone from human tissue banks. Allografts also may be cortical, cancellous, or both. Allograft lacks the array of osteoinductive endogenous compounds intrinsic to autograft, although supplemental products such as demineralized bone matrix paste can be added to encourage new bone formation. Other techniques for increasing the rates of successful fusion are being developed, including the integration of osteoinductive bone morphogenetic proteins, known as BMPs, into the fusion constructs.

PERIPHERAL NERVE

Introduction

Common pathologic processes that compromise function of the peripheral nervous system include mechanical compression, ischemia, inflammation, and neoplasia.

Peripheral Nerve Tumors

Most peripheral nerve tumors are benign and grow slowly. Significant pain increases the likelihood that the patient has a malignant tumor. Treatment for peripheral nerve tumors is surgical resection to establish diagnosis and evaluate for signs of malignancy. These tumors have various degrees of involvement with that parent nerve. Some can be resected with minimal or no damage to the nerve. Tumors that grow within the nerve often contain functioning fascicles. Total excision of these tumors requires sacrifice of the parent nerve. The choice of subtotal resection, nerve preservation, and observation, versus total resection with nerve sacrifice depends on tumor histology and the functions of the parent nerve.

Schwannoma

Schwannomas are the most common peripheral nerve tumors, also referred to as neurilemomas or neurinomas. Most occur in the third decade of life. These benign tumors arise from Schwann cells, which form myelin in peripheral nerves. The most characteristic presentation is a mass lesion with point tenderness and shooting pains on direct palpation. Spontaneous or continuous pain suggests malignancy. They tend to grow slowly and eccentrically on the parent nerve. The eccentric location and discrete encapsulated nature of these tumors often allow total resection without significant damage to the parent nerve. Subtotal resection and observation is reasonable for schwannomas entwined in important nerves, as the incidence of malignant transformation is extremely low.

Neurofibroma

Neurofibromas arise within the nerve and tend to be fusiform masses, unlike schwannomas, which tend to grow out of the nerve. Neurofibromas often present as a mass that is tender to palpation. They usually lack the shooting pains characteristic of schwannomas. Neurofibromas are often difficult to resect completely without sacrifice of the parent nerve. Neurofibromas have a higher incidence of malignant transformation, so patients with known residual tumors require close observation. Patients with von Recklinghausen's neurofibromatosis often have multiple neurofibromas. These patients should be offered resection for symptomatic tumors. They also have a higher risk of malignant degeneration, up to 10. Malignant neurofibromas have the histologic characteristics of sarcoma.

Malignant Nerve Sheath Tumors

Malignant nerve sheath tumors include solitary sarcomas, degenerated neurofibromas, and neuroepitheliomas. Patients with malignant peripheral nerve tumors typically complain of constant pain, rather than pain only on palpation, and are more likely to have

motor and sensory deficits in the distribution of the parent nerve. Treatment for these tumors is radical excision. This often requires sacrifice of the parent nerve. Invasion of nearby soft tissues may occur and necessitate wide resection or amputation in an attempt to prevent systemic metastasis.

Entrapment Neuropathies

Entrapment neuropathy is neurologic dysfunction in nerves passing through a pathologically small, fixed space. Nerve dysfunction may result directly from chronic, repetitive pressure on the nerve, or from ischemic damage due to impaired perfusion.15 Entrapment causing dysfunction of nerve signaling may cause numbness, paresthesias, weakness, or muscle atrophy. By far the two most common sites of entrapment neuropathy are the ulnar nerve at the medial aspect of the elbow and the median nerve at the wrist. Electomyography and nerve conduction studies (EMG/NCS) usually demonstrate slowing across the entrapped segment of nerve. Mechanical peripheral nerve disorders resulting from trauma (brachial plexus disruption, radial nerve damage from humerus fractures, and common peroneal nerve crush injuries) are discussed in the section on trauma.

Ulnar Neuropathy

The ulnar nerve has contributions from the C7, C8, and T1 nerve roots, arises from the medial cord of the brachial plexus, and supplies most of the intrinsic hand muscles (interossei and third and fourth lumbricals), and sensation to the fourth and fifth digits. It passes posteriorly to the medial epicondyle at the elbow in the condylar groove. This segment is superficial and subject to external compression and repetitive minor impacts. Patients with ulnar entrapment at the elbow present with numbness and tingling in the medial palm and the fourth and fifth digits. Motor deficits include weakness and wasting of the intrinsic hand muscles. Treatment for symptomatic ulnar entrapment neuropathy is surgical exploration and incision of the fibrous aponeurotic arch that overlies the nerve. A 6-cm curvilinear incision between the medial epicondyle and the olecranon allows exploration of up to 10 cm of nerve and lysis of compressive tissues.

Carpal Tunnel Syndrome

The median nerve has contributions from the C5 to T1 nerve roots, arises from the medial and lateral cords of the brachial plexus, and supplies the muscles of wrist and finger flexion and sensation to the palmar aspect of the first, second, and third digits. The median nerve passes through the carpal tunnel in the wrist, lying superficial to the four deep and four superficial flexor tendons. The transverse carpal ligament is a tough, fibrous band that forms the roof of the carpal tunnel. The ligament attaches to the pisiform and hamate medially and the trapezium and scaphoid laterally. Patients complain of numbness and tingling in the supplied digits, clumsiness, and worsening with sleep or repetitive wrist movement. Patients may notice wasting of the thenar eminence. Treatment for symptomatic carpal tunnel syndrome unresponsive to splinting, analgesics, and rest is surgical division of the flexor retinaculum. This often provides prompt relief

of pain symptoms and slow recovery of numbness and strength.

Autoimmune and Inflammatory Disorders

These are not surgical diseases, but merit brief mention as they are included in the differential diagnosis for new-onset weakness. Their characteristic presentations help distinguish them from weakness due to structural lesions.

Guillain-Barre Syndrome

Guillain-Barre syndrome is an acute inflammatory demyelinating polyradiculopathy often occurring after viral infection, surgery, inoculations, or mycoplasma infections. Patients classically present with weakness ascending from the legs to the body, arms, and even cranial nerves. Symptoms usually progress over 2 to 4 weeks and then resolve. Care is supportive. Respiratory weakness may require ventilatory support.

Myasthenia Gravis

Myasthenia gravis is an autoimmune process in which antibodies form to the acetylcholine receptors of muscles, leading to fluctuating weakness. Most patients have either thymic hyperplasia or thymoma. The most common symptoms are diplopia, ptosis, dysarthria, and dysphagia. More severe cases have limb or respiratory involvement. Weakness worsens with repetitive movement. Treatment is with acetylcholinesterase inhibitors and possible thymectomy.

Eaton-Lambert Syndrome

Autoimmune process with antibodies to the presynaptic calcium channels. This is a paraneoplastic syndrome most commonly associated with oat cell carcinoma. Patients have weakness of proximal limb muscles that improves with repetitive movement. This diagnosis must prompt oncologic evaluation.

INFECTION

Introduction

Central nervous system infections of interest to neurosurgeons include those that cause focal neurologic deficit due to mass effect, require surgical aspiration or drainage because antibiotic therapy alone is insufficient, cause mechanical instability of the spine, or occur after neurosurgical procedures.

Cranial

Osteomyelitis

The skull is highly vascular and resistant to infections. Osteomyelitis of the skull may

develop by contiguous spread from pyogenic sinus disease or from contamination by penetrating trauma. Staphylococcus aureus and S. epidermidis are the most frequent causative organisms. Patients usually present with redness, swelling, and pain. Contrast head CT aids diagnosis and shows the extent of involved bone, along with associated abscesses or empyema. Osteomyelitis treatment entails surgical debridement of involved bone followed by 2 to 4 months of antibiotics. Craniotomy wound infections are a special concern because performing a craniotomy creates a devascularized free bone flap susceptible to infection and not penetrated by antibiotics. These wounds must be debrided and the bone flaps removed and discarded. Subsequent care involves appropriate antibiotic therapy, observation for signs of recurrent infection off antibiotics, and return to the OR for titanium or methylmethacrylate cranioplasty 6 to 12 months later.

Subdural Empyema

Subdural empyema is a rapidly progressive pyogenic infection. The subdural space lacks significant barriers to the spread of the infection, such as compartmentalization or septations. Subdural empyema usually occurs over the cerebral convexities. Potential infectious sources include sinus disease, penetrating trauma, and otitis. Streptococci and staphylococci are the most frequently found organisms. Presenting symptoms include fever, headache, neck stiffness, seizures, or focal neurologic deficit. Neurologic deficit results from inflammation of cortical blood vessels, leading to thrombosis and stroke. The most common deficit is contralateral hemiparesis. Patients with suggestive symptoms should undergo rapid contrast CT scan. Lumbar puncture frequently fails to yield the offending organism and risks herniation due to mass effect. Typical treatment is wide hemicraniectomy, dural opening, and lavage. The pus may be thick or septated, making burr hole drainage or small craniotomy insufficient. Patients then require 1 to 2 months of antibiotics. Subdural empyema has 10 to 20 mortality and common chronic sequelae, including seizure disorder and residual hemiparesis. However, many patients make a good recovery.

Brain Abscess

Brain abscess is encapsulated infection within the brain parenchyma. It may spread hematogenously in patients with endocarditis or intracardiac or intrapulmonary right-to-left shunts, by migration from the sinuses or ear, or via direct seeding by penetrating trauma. Disorganized cerebritis often precedes formation of the organized, walled-off abscess. Patients may present with nonspecific symptoms such as headache, nausea, or lethargy, or with focal neurologic deficit such as hemiparesis. Alternatively, patients may present in extremis if the abscess ruptures into the ventricular system. Abscesses appear as well-demarcated, ring-enhancing, thin-walled lesions on CT scan and MRI, and often have associated edema and mass effect. Patients require antibiotic therapy after needle aspiration or surgical evacuation. Antibiotic therapy without surgical evacuation may be considered for patients with small, multiple, or critically located abscesses. Abscesses that cause mass effect, decreased mental status, are large, or that fail to decrease in size after a week of antibiotics, should be evacuated. Nonsurgical management still requires aspiration or biopsy for organism culture and sensitivities. Blood and CSF cultures rarely

give definitive diagnosis. Removal of an encapsulated abscess significantly shortens the length of antibiotic therapy required to eliminate all organisms. Common chronic sequelae after successful treatment include seizures or focal neurologic deficit.

Spine

Pyogenic Vertebral Osteomyelitis

Pyogenic vertebral osteomyelitis is a destructive bacterial infection of the vertebrae, usually of the vertebral body. Vertebral osteomyelitis frequently results from hematogenous spread of distant disease, but may occur as an extension of adjacent disease, such as psoas abscess or perinephric abscess. S. aureus and Enterobacter spp. are the most frequent etiologic organisms. Patients usually present with fever and back pain. Diabetics, IV drug abusers, and dialysis patients have increased incidence of vertebral osteomyelitis. Epidural extension may lead to compression of the spinal cord or nerve roots with resultant neurologic deficit. Osteomyelitis presents a lytic picture on imaging and must be distinguished from neoplastic disease. Adjacent intervertebral disc involvement occurs frequently with pyogenic osteomyelitis, but rarely with neoplasia. Plain films and CT help assess the extent of bony destruction or deformity such as kyphosis. MRI shows adjacent soft tissue or epidural disease. Most cases can be treated successfully with antibiotics alone, although the organism must be isolated to steer antibiotic choice. Blood cultures may be positive. Surgical intervention may be required for debridement when antibiotics alone fail, or for stabilization and fusion in the setting of instability and deformity.

Tuberculous Vertebral Osteomyelitis

Tuberculous vertebral osteomyelitis, also known as Pott's disease, occurs most commonly in underdeveloped countries and in immunocompromised people. Several features differentiate tuberculous osteomyelitis from bacterial osteomyelitis. The infection is indolent and symptoms often progress slowly over months. Tuberculosis rarely involves the intervertebral disc. The involved bodies may have sclerotic rather than lytic changes. Multiple nonadjacent vertebrae may be involved. Diagnosis requires documentation of acid-fast bacilli. Treatment involves long-term antimycobacterial drugs. Patients with spinal instability or neural compression from epidural inflammatory tissue should undergo debridement and fusion as needed.

Discitis

Primary infection of the intervertebral disc space, or discitis, is most commonly secondary to postoperative infections. Spontaneous discitis occurs more commonly in children. S. epidermidis and S. aureus account for most cases. The primary symptom is back pain. Other signs and symptoms include radicular pain, fevers, paraspinal muscle spasm, and localized tenderness to palpation. Many cases will resolve without antibiotics. Antibiotics are generally given for positive blood or biopsy cultures or persistent constitutional symptoms. Most patients will have spontaneous fusion across the involved

disc and do not need debridement or fusion.

Epidural Abscess

Epidural abscesses may arise from or spread to the adjacent bone or disc, so distinguishing between vertebral osteomyelitis or discitis and a spinal epidural abscess may be difficult. The most common presenting signs and symptoms are back pain, fever, and tenderness to palpation of the spine. The most significant risk of epidural abscess is weakness progressing to paralysis due to spinal cord or nerve root damage. Cord and root damage may be due to direct compression or to inflammatory thrombosis resulting in venous infarction. S. aureus and Streptococcus spp. are the most common organisms. The source may be hematogenous spread, local extension, or operative contamination. MRI best demonstrates the epidural space and degree of neural compromise. Patients with suspected spinal epidural abscess should undergo surgical debridement for decompression and diagnosis, followed by culture-directed antibiotic therapy. Relative contraindications to surgery include prohibitive comorbidities or total lack of neurologic function below the involved level. Patients with no neurologic deficits and an identified organism may be treated with antibiotics alone and very close observation. This is controversial, however, because these patients can undergo rapid and irreversible neurologic decline. Most epidural abscesses can be accessed via laminectomy without fusion. Collections predominantly anterior to the cervical or thoracic cord may require anterior approach and fusion.

FUNCTIONAL NEUROSURGERY

Epilepsy Surgery

Seizures result from uncontrolled neuronal electrical activity. Seizures may result from irritative lesions in the brain, such as tumors or hematomas, or from physiologic or structural abnormalities. Seizures may involve a part of the brain (focal) or the entire brain (generalized). Focal seizures may be associated with normal consciousness (simple) or decreased consciousness (complex). All generalized seizures cause loss of consciousness. Focal seizures may secondarily generalize. Patients with multiple unprovoked seizures over time have epilepsy. Epilepsy categorization depends on such factors as type of seizures, electroencephalographic (EEG) findings, associated syndromes, and identifiable etiologies. All patients with unexplained seizures (i.e., no obvious cause such as head trauma or alcohol withdrawal) or epilepsy require thorough neurologic evaluation, including imaging to evaluate for a mass lesion. Antiepileptic drugs (AEDs) form the first line of therapy for epilepsy, initially as monotherapy, then as combination therapy. Epilepsy patients who have failed satisfactory trials of several AED combination regimens may be candidates for surgical intervention. Lack of seizure control or patient intolerance of the medications may constitute failure. Epilepsy surgery can decrease the frequency of seizures by resection of the electrical source of the seizures, or decrease the severity of seizures by severing white matter tracts through which the abnormal electrical activity spreads. Three types of epilepsy surgery are discussed. Epilepsy surgery appears to be extremely underutilized, given the relatively

low risk of the procedures, and the crippling social and economic effects of uncontrolled or partially controlled epilepsy.16 Patients with symptoms, imaging abnormalities, and EEG analysis compatible with a specific seizure focus are most likely to have good results from epilepsy surgery.

Anterior Temporal Lobectomy

Medial temporal lobe structural abnormalities can lead to complex partial seizures (CPS). Many patients with CPS have poor seizure control on medications. Patients with CPS may have significant reduction in seizure frequency or cessation of seizures after resection of the anterior temporal lobe. The amygdala and the head of the hippocampus are removed as part of the lobectomy. Resection may be taken back approximately 4.5 cm from the temporal tip in the language-dominant hemisphere, and 6 cm from the temporal tip in the language nondominant hemisphere, with low risk of significant deficits.17 Two main risks of anterior temporal lobectomy are memory problems and visual problems. Removal of the hippocampus in a patient with an atrophied or nonfunctional contralateral hippocampus causes a global memory deficit. Interruption of the optic radiations, which carry visual signals from the contralateral superior visual quadrants of both eyes, causes a contralateral superior quadrantanopia, known as a "pie in the sky" field deficit.

Corpus Callosotomy

Patients with generalized seizures, atonic seizures associated with drop attacks, or absence seizures, who are found to have bilaterally coordinated pathologic cortical discharges on EEG, and who fail AED therapy may be candidates for corpus callosotomy. The corpus callosum is a large white matter tract that connects the cerebral hemispheres. Loss of consciousness requires simultaneous seizure activity in both hemispheres. Focal or partial seizures may spread via the corpus callosum to the contralateral hemisphere, causing generalization and loss of consciousness. Division of the corpus callosum can interrupt this spread. Patients may have decreased numbers of seizures and/or fewer episodes of lost consciousness. Usually only the anterior half or two-thirds of the corpus callosum is divided, as more extensive division increases the risk of disconnection syndrome. Patients with disconnection syndrome are unable to match objects in the opposite visual hemifields, to identify objects held in one hand with the other hemifield, and to write with the left hand or name objects held in the left hand (in left hemisphere-dominant patients).

Hemispherectomy

Children with intractable epilepsy, structural anomalies in one hemisphere, and contralateral hemiplegia, may have improved seizure control after resection of the hemisphere (anatomic hemispherectomy) or disruption of all connections to the hemisphere (functional hemispherectomy). Functional hemispherectomy is often preferred over anatomic hemispherectomy because of the high incidence of complications such as hematoma formation and ventriculoperitoneal shunt dependence associated with

the latter.

Deep Brain Stimulators

Patients with essential tremor and medically refractory Parkinson's disease have abnormal activity in the nuclei of the basal ganglia. The basal ganglia are extrapyramidal structures that modulate and regulate signals in the corticospinal (pyramidal) tracts. Abnormal extrapyramidal activity leads to the loss of the normal modulation of movement and thus the clinical manifestations of the diseases. Fine electrical leads placed in these deep basal ganglia nuclei and connected to pulse generators modify the pathologic signals. The pulse generators are usually placed in the chest in a manner similar to cardiac pacemakers. Connector wires travel from the generators in the subcutaneous space up the neck and in the subgaleal space in the head, to connect the pulse generators to the electrical leads. Proper lead placement is accomplished with stereotactic guidance. A frame is rigidly locked to the patient's head and an MRI is obtained with the frame in place. Calculation of the coordinates of the millimeter-sized deep brain nuclei in relation to the three-dimensional space defined by the fixed frame allows accurate targeting, and the fine electrical leads are placed within the desired nuclei (Fig. 41-32). Postoperatively the pulse generators can be interrogated and adjusted with hand-held, transcutaneous, noninvasive devices as needed for symptom control.

Essential Tremor

Essential tremors are action tremors of 4 to 8 Hz rhythmic oscillation that often affect one arm or the head. Essential tremor often starts in the third or fourth decade of life, and increases in frequency and amplitude with age. Beta blockers decrease symptoms. Patients with poor medical control and significant functional impairment can benefit significantly from placement of a deep brain stimulator in the contralateral ventrointermediate nucleus (VIN) of the thalamus. Placement of VIN stimulators for essential tremors appears to result in durable symptom control with good postoperative neuropsychologic outcomes in properly selected patients.18,19

Parkinson's Disease

Parkinson's disease is a progressive disorder characterized by rigidity, bradykinesia, and resting tremor, due to loss of dopamine-secreting neurons in the substantia nigra and locus ceruleus. It is also known as paralysis agitans. Dopaminergic agents such as levodopa/carbidopa and anticholinergic agents such as amantadine and selegiline form the basis of medical therapy. Patients with poor medical control or significant drug side effects may benefit significantly from placement of bilateral deep brain stimulators in the subthalamic nuclei (STN) or globus pallidus pars interna (GPi). Debate continues regarding the relative efficacy of each target.20 A blinded trial is currently underway through the Veteran's Administration Parkinson's Disease Research, Education, and Clinical Centers (PADRECCs) comparing outcomes with STN and GPi stimulation. Deep brain stimulation seems to provide durable symptom relief with good postoperative neuropsychologic function in properly selected patients.21

Trigeminal Neuralgia

Trigeminal neuralgia, also known as tic douloureux, is characterized by repetitive, unilateral, sharp and lancinating pains in the distribution of one of the three branches of cranial nerve V, the trigeminal nerve. The patient may describe a "trigger point," an area on the face that elicits the pain when touched. A current leading etiologic hypothesis for trigeminal neuralgia is irritation and pulsatile compression of the root entry zone of the nerve by an artery in the posterior fossa, usually a loop of the superior cerebellar artery. The pain is excruciating and can be debilitating. Medical therapy, including carbamazepine and amitriptyline, may reduce the frequency of events. Options for medically refractory cases include percutaneous injection of glycerol into the path of the nerve, peripheral transection of the nerve branches, stereotactic radiosurgery, and microvascular decompression (MVD).

MVD involves performing a small posterior fossa craniotomy on the side of the symptoms, retraction of the cerebellar hemisphere, and exploration of cranial nerve V. If an artery is found near the nerve, the vessel is freed of any adhesions and nonabsorbable material is placed between the nerve root and the artery. MVD remains the first definitive management option because stereotactic radiosurgery is associated with a high incidence of facial numbness.22

STEREOTACTIC RADIOSURGERY

Introduction

The term stereotactic radiosurgery (SRS) refers to techniques that allow delivery of high-dose radiation that conforms to the shape of the target and has rapid isodose fall-off, minimizing damage to adjacent neural structures. The two most common devices used for conformal SRS for intracranial lesions are the LINAC (linear accelerator) and the gamma knife. LINAC delivers a focused beam of x-ray radiation from a port that arcs partway around the patient's head. Linear accelerators are commonly used to provide fractionated radiation for lesions outside the CNS. They are found in most radiation oncology departments. SRS can be performed with these existing units, after upgrades to the software and collimators. The gamma knife delivers approximately 200 focused beams of gamma radiation from cobalt sources through a specially designed colander-like helmet. Gamma knife units are used only for intracranial disease and cost up to $5 million; thus they are most appropriate in high patient-volume centers. There is ongoing debate in the literature regarding the two technologies.23,24,25 Both continue to evolve, allowing more precise and complex isodose conformation to complex lesions. Most lesions can be treated equally well with either technology. Lesions abutting the medulla or the spinal cord should not be treated with SRS, because these structures do not tolerate the radiation dose delivered to structures within millimeters of the target. Also, medullary or spinal cord compression can result from swelling of the lesion after the radiosurgery dose, resulting in devastating neurologic deficit.

Arteriovenous Malformations

SRS has been found to be an effective stand-alone therapy for AVMs up to 3 cm in diameter. SRS is best for lesions that are difficult to access surgically due to high likelihood of postoperative neurologic deficit. SRS is not effective for lesions larger than 3 cm. Effective obliteration and elimination of the risk of hemorrhage takes 2 years. There is an approximately 2 annual incidence of hemorrhage during this 2-year period.26 Thus surgical excision remains the preferred therapeutic modality, with SRS reserved for cases deemed very high-risk for surgery due to location or patient factors.27 Some patients with large AVMs who undergo surgery will have unresectable residual lesions. SRS may be used as an effective adjunctive therapy in these patients.

Vestibular Schwannomas

SRS has been introduced as a therapeutic alternative to microsurgical resection for vestibular schwannomas up to 2.5 cm in maximum diameter. SRS provides high rates of tumor growth arrest and possible reduction in size with low rates of facial nerve palsy. Patients with functional ipsilateral hearing preprocedure may be more likely to retain functional hearing postprocedure than with microsurgery. The limitations of SRS include inability to treat tumors larger than 2.5 cm, the possibility of radiation-induced malignant transformation of these benign tumors, and lack of long-term follow-up. SRS centers are accumulating experience with these tumors and accumulating data on long-term results.28,29 The indications for microsurgery and SRS will continue to evolve. Either approach should be undertaken at a high-volume center, as studies show the patient outcomes improve with increased surgeon experience.30

Intracranial Metastases

Patients with solitary or multiple intracranial metastases may be treated primarily with SRS.31 Patients have improved survival after SRS compared to no treatment or whole-brain radiation therapy (WBRT), and similar survival to patients undergoing total surgical resection. Patients with lesions greater than 3 cm in diameter or evidence of intracranial hypertension should undergo surgical decompression rather than SRS. Some studies show improved survival with up to seven intracranial masses. Patients with multiple intracranial masses have almost zero long-term survival, and most will die of their intracranial disease. Patients with intracranial metastases live 3 to 6 months on average with medical care and WBRT. This can be extended to 9 to 16 months with SRS or surgery, depending on tumor type, age, and patient condition.32

CONGENITAL AND DEVELOPMENTAL ANOMALIES

Dysraphism

Dysraphism describes defects of fusion of the neural tube involving the neural tube itself, or overlying bone or skin. Dysraphism may occur in the spine or the head. Neural tube defects are among the most common congenital abnormalities. Prenatal vitamins,

especially folic acid, reduce the incidence of neural tube defects.

Spina Bifida Occulta

Spina bifida occulta is congenital absence of posterior vertebral elements. The spinous process is always missing, the laminae may be missing to various degrees, but the underlying neural tissues are not involved. Spina bifida occulta is found in 25 of the general population, and is asymptomatic unless associated with other developmental abnormalities.

Spina Bifida with Myelomeningocele

Spina bifida with myelomeningocele describes congenital absence of posterior vertebral elements with protrusion of the meninges through the defect, and underlying neural structural abnormalities. Common findings are weakness and atrophy of the lower extremities, gait disturbance, urinary incontinence, and deformities of the foot. Myelomeningoceles arising from the high lumbar cord usually cause total paralysis and incontinence, while those arising from the sacral cord may have only clawing of the foot and partial urinary function. Myelomeningocele patients often have hydrocephalus and a Chiari II malformation, an abnormal downward herniation of the cerebellum and brain stem through the foramen magnum. Patients with abnormal protrusion of meninges through the bony defect without abnormalities of the underlying neural tissue have a meningocele. Most of these patients are neurologically normal.

Encephalocele

Herniation of brain encased in meninges through the skull that forms an intracranial mass is referred to as encephalocele. Herniation of meninges without brain tissue is referred to as a meningocele. Most occur over the convexity of the skull. More rarely, the tissue protrudes through the skull base into the sinuses. Treatment involves excision of the herniated tissue and closure of the defect. Most patients with encephaloceles and meningoceles have impaired cognitive development. Patients with greater amounts of herniated neural tissue tend to have more severe cognitive deficits.

Craniosynostosis

Craniosynostosis is the abnormal early fusion of a cranial suture line with resultant restriction of skull growth in the affected area and compensatory bulging at the other sutures. Skull growth occurs at the cranial sutures for the first 2 years of life, at the end of which the skull has achieved over 90 of its eventual adult size. Fusion of the sagittal suture, or sagittal synostosis, results in a boat-shaped head, known as scaphocephaly. Unilateral coronal synostosis results in ipsilateral forehead flattening and outward deviation of the orbit, known as plagiocephaly. The contralateral normal forehead appears to bulge by comparison. Bilateral coronal synostosis results in a broad, flattened forehead, known as brachycephaly, and is often associated with maxillary hypoplasia and proptosis. Unilateral or bilateral lambdoid synostosis results in flattening of the occiput.

Occipital flattening can result from abnormal suture fusion (synostosis), or from physical remolding of the skull caused by always placing the baby in the supine position for sleep (known as positional plagiocephaly). Placing the baby in the prone position or tilted onto the contralateral side may restore near-normal skull shape in most cases of lambdoid synostosis, avoiding surgery. Treatment for synostoses in general is surgical, involving resection of the fused suture, or more complex reconstructive techniques for severe or refractory cases.

Hydrocephalus

Excess CSF in the brain that results in enlarged ventricles is known as hydrocephalus. The adult forms approximately 500 mL of CSF per day, much of it in the lateral ventricles. CSF flows from the ventricles to the subarachnoid space, and is then absorbed into the venous blood through the arachnoid granulations. Hydrocephalus may be classified as communicating or obstructive (outlined below), and congenital or acquired. Congenital lesions associated with or causing hydrocephalus include stenosis of the cerebral aqueduct, Chiari malformations, myelomeningoceles, and intrauterine infections. Acquired hydrocephalus may result from occlusion of arachnoid granulations by meningitis or subarachnoid hemorrhage, or occlusion of CSF pathways by adjacent tumors (Fig. 41-33).

Communicating Hydrocephalus

Obstruction at the level of the arachnoid granulations constitutes communicating hydrocephalus. This usually causes dilation of the lateral, third, and fourth ventricles equally. The most common causes in adults are meningitis and subarachnoid hemorrhage. Hydrocephalus may be transient after subarachnoid hemorrhage, with reestablishment of normal CSF absorption after the protein content of the CSF returns to normal and the granulations reopen.

Obstructive Hydrocephalus

Obstruction of CSF pathways is known as obstructive hydrocephalus. Ventricles proximal to the obstruction dilate, while those distal to the obstruction remain normal in size. Typical patterns include dilation of the lateral ventricles due to a colloid cyst occluding the foramen of Monro, dilation of the lateral and third ventricles due to a tectal (midbrain) glioma or pineal region tumor occluding the cerebral aqueduct, or dilation of the lateral and third ventricles with obliteration of the fourth ventricle by an intraventricular tumor of the fourth ventricle. Obstructive hydrocephalus may present precipitously and require urgent shunting to prevent herniation.

Chiari I Malformation

Chiari I malformation is the caudal displacement of the cerebellar tonsils below the foramen magnum, and may be seen as an incidental finding on MRI scans in asymptomatic patients. Symptomatic patients usually present with headache, neck pain,

or symptoms of myelopathy, including numbness or weakness in the extremities. The brain stem and lower cranial nerves are normal in Chiari I malformations. Chiari II malformations are more severe and involve caudal displacement of the lower brain stem and stretching of the lower cranial nerves. Symptomatic patients may be treated with suboccipital craniectomy to remove the posterior arch of the foramen magnum, along with removal of the posterior ring of C1. Removal of these bony structures relieves the compression of the cerebellar tonsils and cervicomedullary junction, and may allow reestablishment of normal CSF flow patterns. Figure 41-34 demonstrates typical MRI appearance of a Chiari I malformation.

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