clinical neuroanatomy 7th ed - snell, richard s

Frontmatter Copyright Authors Preface Acknowledgments Color Atlas of Brain 1 - Introduction and Organization of the Nervous System 2 - The Neurobiology of the Neuron and the Neuroglia 3 - Nerve Fibers, Peripheral Nerves, Receptor and Effector Endings, Dermatomes, andMuscle Activity 4 - The Spinal Cord and the Ascending and Descending Tracts 5 - The Brainstem 6 - The Cerebellum and Its Connections 7 - The Cerebrum 8 - The Structure and Functional Localization of the Cerebral Cortex 9 - The Reticular Formation and the Limbic System 10 - The Basal Nuclei (Basal Ganglia) and Their Connections 11 - The Cranial Nerve Nuclei and Their Central Connections and Distribution 12 - The Thalamus and Its Connections 13 - The Hypothalamus and Its Connections 14 - The Autonomic Nervous System 15 - The Meninges of the Brain and Spinal Cord 16 - The Ventricular System, the Cerebrospinal Fluid, and the Blood-Brain and Blood-Cerebrospinal Fluid Barriers 17 - The Blood Supply of the Brain and Spinal Cord 18 - The Development of the Nervous System Appendix

Authors: Snell, Richard S.Title: Clinical Neuroanatomy, 7th Edition

Copyright ©2010 Lippincott Williams & Wilkins

2010

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Library of Congress Cataloging-in-Publication Data

Snell, Richard S.

Clinical neuroanatomy / Richard S. Snell. — 7th ed.

p. ; cm.

Includes bibliographical references and index.

ISBN 978-0-7817-9427-5

1. Neuroanatomy. I. Title.

[DNLM: 1. Nervous System—anatomy & histology. WL 101 S671c 2010]

QM451.S64 2010

616.8—dc22

2008040897

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Care has been taken to confirm the accuracy of the information present and to describe generally accepted practices.However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences fromapplication of the information in this book and make no warranty, expressed or implied, with respect to the currency,completeness, or accuracy of the contents of the publication. Application of this information in a particular situationremains the professional responsibility of the practitioner; the clinical treatments described and recommended may not beconsidered absolute and universal recommendations.

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> Front of Book > Authors

Author

Richard S. Snell M.R.C.S., L.R.C.P., MB, BS, MD, PhDEmeritus Professor of AnatomyGeorge Washington University, School of Medicine and Health Sciences, Washington, DC; Formerly Associate Professorof Anatomy and Medicine, Yale University Medical School; Lecturer in Anatomy King's College University of London; andVisiting Professor of Anatomy, Harvard Medical School.



> Front of Book > Preface

Preface

This book contains the basic neuroanatomical facts necessary for the practice of medicine. It is suitable for medicalstudents, dental students, nurses, and allied health students. Residents fnd this book useful during their rotations.

The functional organization of the nervous system has been emphasized and indicates how injury and disease can result inneurologic deficits. The amount of factual information has been strictly limited to that which is clinically important.

In this edition, the content of each chapter has been reviewed, obsolete material has been discarded, and new materialadded.

Each chapter is divided into the following categories:

Clinical Example. A short case report that serves to dramatize the relevance of neuroanatomy introduces each chapter.

Chapter Objectives. This section details the material that is most important to learn and understand in each chapter.

Basic Neuroanatomy. This section provides basic information on neuroanatomical structures that are of clinicalimportance. Numerous examples of normal radiographs, CT scans, MRIs, and PET scans are also provided. Many cross-sectional diagrams have been included to stimulate students to think in terms of three-dimensional anatomy, which is soimportant in the interpretation of CT scans and MRI images.

Clinical Notes. This section provides the practical application of neuroanatomical facts that are essential in clinicalpractice. It emphasizes the structures that the physician will encounter when making a diagnosis and treating a patient.It also provides the information necessary to understand many procedures and techniques and notes the anatomical“pitfalls” commonly encountered.

Clinical Problem Solving. This section provides the student with many examples of clinical situations in which aknowledge of neuroanatomy is necessary to solve clinical problems and to institute treatment; solutions to the problemsare provided at the end of the chapter.

Review Questions. The purpose of the questions is threefold: to focus attention on areas of importance, to enablestudents to assess their areas of weakness, and to provide a form of self-evaluation when questions are answered underexamination conditions. Some of the questions are centered around a clinical problem that requires a neuroanatomicalanswer. Solutions to the problem are provided at the end of each chapter.

In addition to the full text from the book, an interactive Review Test, including over 450 questions, is provided online.

The book is extensively illustrated. The majority of the figures have been kept simple and are in color. As in the previousedition, a concise Color Atlas of the dissected brain is included prior to the text. This small but important group of coloredplates enables the reader to quickly relate a particular part of the brain to the whole organ.

References to neuroanatomical literature are included should readers wish to acquire a deeper knowledge of an area ofinterest.

R. S. S.



> Front of Book > Acknowledgments

Acknowledgments

Iam greatly indebted to the following colleagues who provided me with photographic examples of neuroanatomical material:Dr. N. Cauna, Emeritus Professor of Anatomy, University of Pittsburgh School of Medicine; Dr. F. M. J. Fitzgerald,Professor of Anatomy, University College, Galway, Ireland; and Dr. A. Peters, Professor of Anatomy, Boston UniversitySchool of Medicine.

My special thanks are owed to Larry Clerk, who, as a senior technician in the Department of Anatomy at the GeorgeWashington University School of Medicine and Health Sciences, greatly assisted me in the preparation of neuroanatomicalspecimens for photography.

I am also grateful to members of the Department of Radiology for the loan of radiographs and CT scans that have beenreproduced in different sections of this book. I am most grateful to Dr. G. Size of the Department of Radiology at YaleUniversity Medical Center for examples of CT scans and MRI images of the brain. I also thank Dr. H. Dey, Director of thePET Scan Unit of the Department of Radiology, Veterans Affairs Medical Center, West Haven, Connecticut, for severalexamples of PET scans of the brain. I thank the medical photographers of the Department of Radiology at Yale for theirexcellent work in reproducing the radiographs.

As in the past, I express my sincere thanks to Myra Feldman and Ira Grunther, AMI, for the preparation of the very fineartwork.

Finally, to the staff of Lippincott Williams & Wilkins, I again express my great appreciation for their continued enthusiasmand support throughout the preparation of this book.



> Front of Book > Color Atlas of Brain

Color Atlas of Brain

Figure CA-1 Top: Superior view of the brain. Bottom: Inferior view of the brain.

Figure CA-2 Top: Anterior view of the brain. Bottom: Posterior view of the brain.

Figure CA-3 Top: Right lateral view of the brain. Bottom: Medial view of the right sideof the brain following median sagitttal section.

Figure CA-4 Coronal sections of the brain passing through the anterior horn of thelateral ventricle (top), the mammillary bodies (middle), and the pons (bottom).

Figure CA-5 Top: Horizontal section of the cerebrum showing the lentiform nucleus,the caudate nucleus, the thalamus, and the internal capsule. Bottom: Oblique coronalsection of the brain.

Figure CA-6 Top: Inferior view of the brain showing cranial nerves. The abducent andfacial nerves cannot be seen. Bottom: Enlarged inferior view of the central part of thebrain.

Figure CA-7 Top: Posterior view of the brainstem. The greater part of the cerebellumhad been removed to expose the floor of the fourth ventricle. Middle: Superior view ofthe cerebellum showing the vermis and right and left cerebellar hemispheres. Bottom:Inferior view of the cerebellum showing the vermis and right and left cerebellarhemispheres.

Figure CA-8 Enlarged medial view of the right side of the brain following mediansagittal section, showing the continuity of the central canal, fourth ventricle, cerebralaqueduct, and the third ventricle and entrance into the lateral ventricle through theinterverntricular foramen.



> Back of Book > Appendix

Appendix

Important Neuroanatomical Data of Clinical Significance

Baseline of the SkullThe baseline of the skull extends from the lower margin of the orbit backward through the upper margin of the externalauditory meatus. The cerebrum lies entirely above the line, and the cerebellum lies in the posterior cranial fossa belowthe posterior third of the line (Fig. A-1).

Falx Cerebri, Superior Sagittal Sinus, and the Longitudinal Cerebral FissureBetween the Cerebral HemispheresThe position of the falx cerebri, superior sagittal sinus, and the longitudinal cerebral fissure between the cerebralhemispheres can be indicated by passing a line over the vertex of the skull in the sagittal plane that joins the root of thenose to the external occipital protuberance.

Parietal EminenceThe parietal eminence is a raised area on the lateral surface of the parietal bone that can be felt about 2 inches (5 cm)above the auricle. It lies close to the lower end of the central cerebral sulcus of the brain (Fig. A-1).

PterionThe pterion is the point where the greater wing of the sphenoid bone meets the anteroinferior angle of the parietal bone.Lying 1-1/2 inches (4 cm) above the midpoint of the zygomatic arch (Fig. A-1), it is not marked by an eminence or adepression, but it is important since the anterior branches of the middle meningeal artery and vein lie beneath it.

Clinical Neuroanatomy of Techniques for Treating Intracranial Hematomas

Burr Holes

Indications for Burr HolesCranial decompression is performed in a patient with a history of progressive neurologic deterioration and signs of brainherniation, despite adequate medical treatment. The presence of a hematoma should be confirmed by a computedtomography scan, if possible.

Anatomy of the Technique for a Temporal Burr Hole

1. The patient is placed in a supine position with the head rotated so that the side for the burr hole is uppermost. Forexample, in a patient with a right-sided fixed and dilated pupil, indicating herniation of the right uncus with pressure on

the right oculomotor nerve, a hematoma on the right side must be presumed, and a burr hole is placed on the rightside.

2. The temporal skin is shaved and prepared for surgery in the usual way.

3. A 3-cm vertical skin incision is made two fingerbreadths anterior to the tragus of the ear and three fingerbreadthsabove this level (Fig. A-2).

4. The following structures are then incised:

a. Skin.

b. Superficial fascia containing small branches of the superficial temporal artery.

c. Deep fascia covering the outer surface of the temporalis muscle.

d. The temporalis muscle is then incised vertically down to the periosteum of the squamous part of the temporal bone(Fig. A-2).

e. The temporalis muscle is elevated from its attachment to the skull, and a retractor is positioned (some muscularbleeding will be encountered).

f. A small hole is then drilled through the outer and inner tables of the skull at right angles to the skull

surface, and the hole is enlarged with a burr (unless a blood clot is present between the inner table and the endosteallayer of dura).

Figure A-1 Surface landmarks on the right side of the head. The relation of themiddle meningeal artery and the brain to the surface of the skull is shown.

g. The white meningeal layer of dura is flexible and gives slightly on gentle pressure.

h. The hole may be enlarged with a curette, and bleeding from the diploe may be controlled with bone wax.

The surgical wound is closed in layers with interrupted sutures placed in the temporalis muscle, the deep fascia covering thetemporalis muscle, and the scalp.

Burr Hole for Epidural HematomaOnce the inner table of the squamous part of the temporal bone (or the anterior inferior angle of the parietal bone) ispierced with a small bit and enlarged with a burr, the dark red clotted blood beneath the endosteal layer of dura is usuallyeasily recognized. However, bright red liquid blood means that the middle meningeal artery or one of its branches isbleeding. The meningeal artery is located deep to the clot and between the endosteal layer of dura and the meningeal layerof dura or in the substance of the endosteal layer of dura; or it may lie in a tunnel of bone.

Burr Hole for Subdural HematomaWhen the squamous part of the temporal bone is penetrated, as described earlier, the endosteal layer of dura will beexposed. In this case, there is no blood clot between the endosteal layer of dura and the meningeal layer of dura, but bothfused layers of dura will be dark bluish. The dura (endosteal and meningeal layers) is gently incised to enter the spacebetween the meningeal layer of dura and the arachnoid mater. The subdural blood usually gushes out, leaving theunprotected brain covered only by arachnoid and pia mater in the depths of the hole.

Clinical Neuroanatomy of the Technique of Ventriculostomy

Indications for VentriculostomyVentriculostomy is indicated in acute hydrocephalus, in which there is a sudden obstruction to the flow of cerebrospinalfluid.

Anatomy of the Technique of VentriculostomyTo perform a ventriculostomy, the needle is inserted into the lateral ventricle through either a frontal or parietal burr hole.The anatomy of these burr holes has been described previously. The needle is inserted through the burr hole using thefollowing anatomical landmarks.

1. Frontal Approach. The needle is inserted through the frontal burr hole and is directed downward and forward in thedirection of the inner canthus of the ipsilateral eye (Fig. A-3).

Figure A-2 A: Surface landmarks for a temporal burr hole. B: The vertical incisionpasses through the temporalis muscle down to bone. The middle meningeal arterylies between the endosteal and meningeal layers of dura and is embedded in theendosteal layer of dura or lies in a bony tunnel.

Figure A-3 Ventriculostomy. Needles passing through frontal or parietal burr holesto enter the lateral ventricle area are shown. The needle is inserted to a depth ofabout 2 inches (5.5 cm) from the skull opening in order to enter the lateral ventricle.

2. Parietal Approach. The needle is inserted through the parietal burr hole and is directed downward and forward in thedirection of the pupil of the ipsilateral eye (Fig. A-3).

The needle is inserted to a depth of about 2 inches (5.5 cm) from the skull opening; in cases of chronic hydrocephalus withgross dilatation of the ventricles, the depth of penetration to the ventricular cavity may be much less.

Vertebral Numbers and Spinal Cord SegmentsTable A-1 relates which vertebral body is related to a particular spinal cord segment.

Table A-1

Vertebrae Spinal Segment

Cervical vertebrae Add 1

Upper thoracic vertebrae Add 2

Lower thoracic vertebrae (7–9) Add 3

Tenth thoracic vertebra L1-2 cord segments

Eleventh thoracic vertebra L3-4 cord segments

Twelfth thoracic vertebra L5 cord segment

First lumbar vertebra Sacral and coccygeal cord segments

Segmental Innervation of MusclesIt is possible to test for the integrity of the segmental innervation of muscles by performing the following simple musclereflexes on the patient.

Biceps brachii tendon reflex C5-6 (flexion of the elbow joint by tapping the biceps tendon).

Triceps tendon reflex C6-7 and 8 (extension of the elbow joint by tapping the triceps tendon).

Brachioradialis tendon reflex C5-6 and 7 (supination of the radioulnar joints by tapping the insertion of thebrachioradialis tendon).

Abdominal superficial reflexes (contraction of underlying abdominal muscles by stroking the skin). Upper abdominalskin T6-7; middle abdominal skin T8-9; lower abdominal skin T10–12.

Patellar tendon reflex (knee jerk) L2, 3, and 4 (extension of knee joint on tapping the patellar tendon).

Achilles tendon reflex (ankle jerk) S1 and 2 (plantar flexion of ankle joint on tapping the Achilles tendon–tendocalcaneus).

Relationship Between Possible Intervertebral Disc Herniations and SpinalNerve RootsIt is useful to be able to relate possible nucleus pulposus herniations with spinal nerve roots. These are shown for thecervical and lumbar regions in Figure A-4.

A correlation between the nerve roots involved, the pain dermatome, the muscle weakness, and the missing or diminishedreflex is shown in Table A-2.

Table A-2 Correlation Between Nerve Roots Involved, the PainDermatome, the Muscle Weakness, and the Missing or

Diminished Reflex

RootInjury

Dermatome Pain Muscles Supplied Movement Weakness Reflex Involved

C5Lower lateralaspect ofupper arm

Deltoid and bicepsShoulderabduction,elbow flexion

Biceps

C6Lateral aspectof forearm

Extensor carpiradialis longus andbrevis

Wrist extensors Brachioradialis

C7 Middle fingerTriceps and flexorcarpi radialis

Extension ofelbow andflexion of wrist

Triceps

C8Medial aspectof forearm

Flexor digitorumsuperficialis andprofundus

Finger flexion None

L1 Groin Iliopsoas Hip flexion Cremaster

L2Anterioraspect of thigh

Iliopsoas, sartorius,hip adductors

Hip flexion, hipadduction

Cremaster

L3Medial aspectof knee

Iliopsoas, sartorius,quadriceps, hipadductors

Hip flexion,knee extension,hip adduction

Patellar

L4Medial aspectof calf

Tibialis anterior,quadriceps

Foot inversion,knee extension

Patellar

L5Lateral part oflower leg anddorsum of foot

Extensor hallucislongus, extensordigitorum longus

Toe extension,ankledorsiflexion

None

S1Lateral edgeof foot

Gastrocnemius,soleus

Ankle plantarflexion

Ankle jerk

S2Posterior partof thigh

Flexor digitorumlongus, flexorhallucis longus

Ankle plantarflexion, toeflexion

None

Figure A-4 A, B: Posterior views of vertebral bodies in the cervical and lumbar regionsshowing the relationship that might exist between herniated nucleus pulposus (pink)and spinal nerve roots. Note that there are eight cervical nerves and only sevencervical vertebrae. In the lumbar region, for example, the emerging L4 nerve rootspass out laterally close to the pedicles of the fourth lumbar vertebra and are notrelated to the intervertebral disc between the fourth and the fifth lumbar vertebrae.Pressure on the L5 motor nerve root produces weakness of plantar flexion of the anklejoint.

Surface Landmarks for Performing a Spinal TapTo perform a spinal tap, the patient is placed in the lateral prone position or in the upright sitting position. The trunk isthen bent well forward to open up to the maximum the space between adjoining laminae in the lumbar region. A grooveruns down the middle of the back over the tips of the spines of the thoracic and the upper four lumbar vertebrae. Thespines are made more prominent when the vertebral column is flexed. An imaginary line joining the highest points on theiliac crests passes over the fourth lumbar spine. With a careful aseptic technique and under local anesthesia, the spinal tapneedle, fitted with a stylet, is passed into the vertebral canal above or below the fourth lumbar spine.

Figure A-5 A: Structures penetrated by the spinal tap needle before it reaches thedura mater. B: Important anatomic landmarks when performing a spinal tap. Althoughthis is usually performed with the patient in a lateral recumbent position with thevertebral column well flexed, the patient may be placed in the sitting position andbent well forward.

Structures Pierced by the Spinal Tap NeedleThe following structures are pierced by the needle before it enters the subarachnoid space (Fig. A-5):

1. Skin

2. Superficial fascia

3. Supraspinous ligament

4. Interspinous ligament

5. Ligamentum flavum

6. Areolar tissue containing the internal vertebral venous plexus in the epidural space

7. Dura mater

8. Arachnoid mater

Table A-3 The Physical Characteristics and Composition of theCerebrospinal Fluid

Appearance Clear and colorless

Volume c. 150 mL

Rate of production 0.5 mL/minute

Pressure (lumbarpuncture)

60–150 mm of water (with patient in lateral recumbentposition)

Composition

Protein 15–45 mg/100 mL

Glucose 50–85 mg/100 mL

Chloride 720–750 mg/100 mL

Number of cells 0–3 lymphocytes/cumm

The depth to which the needle will have to pass will vary from an inch or less in children to as much as 4 inches (10 cm) inobese adults.

The pressure of the cerebrospinal fluid in the lateral recumbent position is normally about 60 to 150 mm of water.

See Table A-3 for physical characteristics and composition of the cerebrospinal fluid.

clinical neuroanatomy 7th ed - snell, richard s

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