Radiological Imaging of Brachial plexuses pathology.

Dr/ ABD ALLAH NAZEER. MD.

The brachial plexus is a complex neural network formed by lower cervical and upper thoracic ventral nerve roots which supplies motor and sensory innervations to the upper limb and pectoral girdle. It is located in the neck extending into the axilla posterior to the clavicle.Summaryorigin: ventral rami of C5 to T1course: emerges between anterior and middle scalenes, courses through the posterior triangle of neck posterior to the clavicle before becoming closely associated with the axillary artery in the axilla before giving up its terminal branches or alternatively the roots emerge from behind the anterior scalenes to form 3 trunks which pass between anterior and medial scalenes, then each trunk divides into an anterior and posterior division which pass behind the clavicle, the divisions combine to form 3 cords which surround the second part of the axillary artery, and finally the cords terminate as the 5 major nervesmajor (terminal) branches

median nerveulnar nerveradial nerveaxillary nervemusculocutaneous nerve

motor supply: upper limb and pectoral girdlesensory supply: upper limb and part of the upper thorax

Gross anatomyThe brachial plexus consists of roots, trunks, divisions, cords and terminal branches as it travels from proximal to distal upper limb. This mnemonic describes the order of these subdivisions.RootsRoots are formed between the scalenes anterior and scalenus medius muscles by the anterior rami of C5-C8 and T1 nerve roots. Three branches arise from the roots directly 2:dorsal scapular nerve: arises from the posterior aspect of the C5 root and supplies the rhomboidssubclavian nerve: arises from the C5 and C6 roots anteriorly to supply subclavius (although some texts describe this nerve arising from the superior trunk)long thoracic nerve: arises from the posterior aspects of C5-C7 and supplies serratus anteriorIn addition, the scaleni and longus colli muscles are supplied by multiple variable unnamed muscular branches that arise from all or some of the roots.It is important to remember that although not part of the brachial plexus:the dorsal rami course posteriorly into the spinal extensors (erector spinae) and do not contribute to the brachial plexus.the ventral rami of C4 and C5 also contribute to the phrenic nervethe ventral ramus of T1 also contributes to the first intercostal nerve

TrunksTrunks form from the roots as they pass between scalenus anterior and medius muscles, then go on to traverse the posterior triangle:C5 and C6 roots combine to form the upper or superior trunkC7 root makes up the middle trunkC8 and T1 roots combine to form the lower or inferior trunkOne branch arises from the trunks:suprascapular nerve: arises from the upper trunk and supplies the supraspinatus and infraspinatus muscles, and sensation to the glenohumeral and acromioclavicular jointsDivisionsEach trunk divides to form an anterior and posterior division posterior to the mid clavicle. In general anterior divisions supply muscles of the anterior compartments (flexors) whereas the posterior divisions supply muscles of the posterior compartments (extensors). No branches arise from the divisions.CordsThe divisions then combine to form cords, which are named for their relation to the second part of the axillary artery:lateral cord is formed by the union of the upper two anterior divisions at the lateral border of the first ribmedial cord is a continuation of the lower anterior divisionposterior cord consists of the united three posterior divisionsThe prevertebral fascia of the neck extends down to ensheath the axillary artery and cords. It is into this axillary sheath that local anaesthetic is injected when performing a brachial plexus block.

Peripheral nerves (branches)Various peripheral nerves, also termed "branches", then branch from these cords.Branches from the lateral cord are:lateral pectoral nerveterminal branches

musculocutaneous nervelateral root of the median nerve

Branches from the posterior cord are:upper subscapular nervethoracodorsal nervelower subscapular nerveterminal branches

radial nerveaxillary nerve

Branches from the medial cord are:medial pectoral nervemedial cutaneous nerve of the armmedial cutaneous nerve of the forearmterminal branches

medial root of the median nerveulnar nerve

Coronal MRI scan shows the normal appearance of the brachial plexus – you can see the C5, C6 and C7 nerve roots emerging from the vertebrae and converging further down into the trunks, divisions and roots.

Common presenting symptomsPresenting symptoms referable to the BP can range from vague and nonspecific (e.g., regional shoulder pain, upper extremity weakness, or altered upper extremity/shoulder sensorium) to symptoms with specific nerve distribution (e.g., pain or motor/sensory deficit). More specific symptoms such as scapular winging (due to long thoracic nerve injury), diaphragmatic dysfunction (involvement of the phrenic nerve C3-C5), or Horner’s syndrome (postganglionic C8-T1 involvement) can also be presenting complaints.Pathology categorizationDisease processes affecting the brachial plexus can be subdivided into the following broad categories: traumatic injury and several nontraumatic subtypes, including: infection, inflammatory brachial neuritis/neuropathy, benign or malignant neoplasms, radiation-induced plexopathy, vascular abnormalities, and compression of the plexus.Traumatic injuryPerhaps the most significant utility of brachial plexus MR in the setting of trauma is to differentiate pre and post ganglionic injury, a distinction that has significant management implications. Identification of a preganglionic injury can be difficult and often requires recognition of a combination of direct (e.g., high resolution 3D MRI or CT myelography) and indirect imaging characteristics.

Direct signsHigh-resolution 3D T2- and CT myelography images can show anatomical continuity or lack thereof of intradural nerve rootlets. The course of the rootlets should be followed from the root entry zone to the DRG in the neural foramen. In the setting of a structurally intact yet injured nerve root, post contrast sequences may show abnormal enhancement of the injured nerve root relative to the control side.Indirect signsA traumatic pseudomeningocele may be present on T2-weighted images. The pseudomeningocele will usually show invagination into the affected neural foramen, with or without the detached nerve root within it. Contralateral deviation of the spinal cord is another indirect sign. Normally, the nerve rootlets anchor the spinal cord in the middle of the thecal sac, much like the taut ropes attached to large tents. Avulsion of nerve rootlets results in unopposed traction by the contralateral, intact nerve rootlets. Postganglionic traumatic injuries can demonstrate focal edema (hyperintense T2 signal) involving any part of the plexus distal to the DRG, anatomic discontinuity with or without clumping/retraction, or a peri-plexus hematoma.

InfectionInfection of the brachial plexus can arise from a variety of sources, but it usually spreads directly from an adjacent structure such as an extension of spinal osteomyelitis, empyema/pulmonary parenchymal infections, glenohumeral septic arthritis, overlying soft tissue infection, or iatrogenic introduction of pathogens.2,15,16 Imaging characteristics of brachial plexus infections are similar to infectious processes elsewhere in that they result in T2 hyperintense edema, variable enhancement pattern (non-mass like), surrounding soft tissue inflammation and presence or absence of a demonstrable source collection.InflammationSpontaneous brachial plexitis, also known as Parsonage Turner Syndrome, typically presents with the constellation of spontaneous acute severe burning shoulder pain, subsequent sensory disturbance, and delayed weakness and atrophy. The inflammatory processes involving structures adjacent to the brachial plexus can also secondarily involve the brachial plexus. The imaging characteristics of brachial plexus inflammation are nonspecific but consistent with inflammatory conditions elsewhere in the body. Commonly encountered features include T2 hyperintensity, thickening and variable enhancement of brachial plexus components, as well as enlargement of the affected shoulder girdle muscle with enhancement and hyperintense T2 signal (signs of acute/subacute denervation).

Benign neoplasmsA variety of benign lesions can involve the brachial plexus. Specifically, these entities include fibromatosis, proliferative fasciitis, lipoma, hemangioma, brachial cleft cyst, lymphangioma, and benign neural and nerve sheath neoplasms . Fibromatosis (extra-abdominal desmoid) and proliferative fasciitis can both present as rather large masses involving the brachial plexus, with the former usually presenting as painless, and the latter as exquisitely tender. Both of these lesions typically demonstrate T1 isointensity to surrounding muscle/soft tissue, heterogeneous T2 hyperintensity, with mild enhancement in the case of proliferative fasciitis and avid enhancement in fibromatosis.Lesions such as lymphangiomas, lipomas, brachial cleft cysts, and hemangiomas occur rarely in the BP and demonstrate similar imaging characteristics as they would in other areas of the body. Lipomas are usually easily discernible from non fatty lesions, as they characteristically demonstrate T1 and T2 hyperintensity, with signal dropout on fat-saturated sequences. One potential pitfall is differentiating benign lipoma from low-grade liposarcoma. In the setting of large lesions (>10 cm), significant non-fatty components, numerous septae, or heterogeneous enhancement, PET-CT can be performed for better characterization.Benign nerve sheath tumors have been described in a plethora of prior publications. Briefly, they are commonly observed as T2 hyperintense lesions in the neural foramen, sometimes resulting in expansion and osseous remodeling.

Malignant neoplasmsMalignant lesions can either primarily arise within the brachial plexus or spread to the brachial plexus secondarily. Primary malignant lesions involving the brachial plexus are predominately sarcomatous (low grade sarcoma, radiation induced sarcoma, osteosarcoma, Ewing Sarcoma, leiomyosarcoma, liposarcoma). These soft tissue masses often demonstrate overlapping imaging characteristics and can be difficult to differentiate based on imaging alone. Primary mesothelioma, malignant nerve sheath tumors and involvement from primary vertebral tumors such as chondrosarcoma or chordoma are also rarely seen involving the brachial plexus.In regards to metastatic disease, the most common primary malignancies are breast, lung, lymphoma, and head/neck cancer. Lung adenocarcinoma typically secondarily involves the brachial plexus via direct extension in the setting of a Pancoast tumor involving the superior sulcus. Breast carcinoma (Figure 8), lymphoma, and head/neck malignancies usually involve the brachial plexus via metastatic regional lymphatic spread In the setting of primary or metastatic brachial plexus involvement it is important to determine presence or absence of leptomeningeal enhancement/spread, relation to the ipsilateral vertebral artery, and extent of nerve root involvement.

Radiation plexopathyRadiation plexopathy typically manifests as T2 hypointense thickening of the brachial plexus components without focal mass. In the setting of prior malignancy and local radiation to the brachial plexus, it is crucial for the clinician to attempt to differentiate tumor progression/recurrence from benign radiation-induced plexopathy changes. Time course is key to discerning these entities, as radiation induced plexopathy occurs between 5 and 30 months post radiation therapy (peak incidence 10-20 months post radiation). Furthermore, details of clinical presentation can help aid in diagnosis. For example, increasing/new pain or new Horner syndrome are more likely to reflect tumor recurrence/progression; while unilateral edema or parasthesia is more likely to reflect radiation-induced plexopathy.Compression of the brachial plexusThe neurovascular bundle can be compressed at several areas along the brachial plexus, resulting in a clinical constellation of symptoms commonly referred to as thoracic outlet syndrome. Particularly, the brachial plexus components can be affected at the interscalene triangle, costoclavicular space, or less commonly, the pectoralis minor space. Clinically, this syndrome can result in ulnar distribution hand weakness, hand/arm/neck pain/parasthesias, and upper extremity muscle atrophy. Symptomatology is often exacerbated/reproducible by arm raise. The syndrome is typically caused by anatomic variants such as a cervical rib, prominent lower cervical transverse processes, posttraumatic fibrous bands, or pectoralis muscle hypertrophy. MRI can be used to identify any of the aforementioned causative factors, and should include provocative testing in order to reproduce Symptomatology during the time of the scan.

Vascular abnormalitiesA variety of space-occupying vascular abnormalities can result in brachial plexus compression, including but not limited to pseudo aneurysm, arteriovenous fistula (AVF), or arteriovenous malformation (AVM).2 The involved vessels include the subclavian, axillary, common carotid, and vertebral arteries. A variety of predisposing conditions can result in these lesions, which are best characterized on dedicated vascular studies such as CT angiography, MR angiography, and/or conventional angiography.

The Axial T2FS and Coronal STIR SPACE images: Pseudomeningoceles of C3-4 to C6-7 levels with avulsed nerve roots (arrows). Coronal STIR SPACE image: Asymmetrical atrophy of the distal right brachial plexus segments (arrows).

Avulsion injuries in 26-year-old man with weakness and pain in upper extremity after motorcycle crash. Coronal fat-suppressed T2-weighted image shows bright fluid filled pseudomeningoceles (arrows) in course of C8 and T1 nerve roots.

Avulsion injuries in 26-year-old man. Coronal post gadolinium T1-weighted image (A) and parasagittal T2-weighted image (B) show posttraumatic pseudomeningoceles (arrows) involving C7 and C8 nerve roots.

Stretching (“burning”) injury of right brachial plexus in 35-year-old man. Coronal fat-suppressed T2-weighted image shows that there is high signal, indicating edema, and thickening of divisions and cords (straight arrows) of right brachial plexus. Note effusion (curved arrow) in ipsilateral shoulder joint due to traction injury of upper extremity.

57-year-old woman who had undergone surgery and irradiation for treatment of left-sided breast carcinoma and was doing well until about 7 months after termination of radiation therapy, when she developed weakness and pain in left upper extremity. Coronal fat-suppressed T2-weighted image shows diffuse thickening and increased signal intensity (arrow) in region of left brachial plexus affecting trunks, divisions, and cords.

Coronal fat-suppressed T2-weighted image shows mild thickening and increased signal in trunks for left brachial plexus in 45-year-old man who presented with sudden onset of weakness in ipsilateral upper extremity. Symptoms resolved spontaneously 4 weeks later; this case was assumed to be a virus-induced plexopathy.

65-year-old man presenting with left-sided mixed (i.e., motor and sensory) brachial plexopathy of 2 months' duration. Patient also has history of cigarette smoking and persistent cough that developed 3 weeks earlier. Chest radiography (not shown) revealed abnormal findings. Coronal T1-weighted image shows large left tumor (arrow); note normal interscalene fat pad on right. Obliteration of this fat by tumor as seen here generally implies invasion of brachial plexus at level of trunks that normally course between scalene muscles in interscalene fat pad.

Small left Pancoast's tumor in 60-year-old woman. Coronal T1-weighted image shows small bilobed mass (white arrow) in left lung apex. Note preservation of normal interscalene fat pad (black arrow), which on coronal images has triangular appearance. Left brachial plexus (arrowhead) is nicely seen.

Schwannoma in 45-year-old woman. Coronal fat-suppressed T2-weighted image shows mass with high signal intensity (lower arrow) in region of roots and trunks of right brachial plexus. Note “tail” of mass extending into C7-T1 right neural foramen (upper arrows). This finding is typical of nerve sheath tumors.

Lipoma in 44-year-old woman. Coronal T1-weighted image (A) and corresponding fat-suppressed image (B) show well-defined fatty mass (arrows)

that typically loses all signal intensity after fat-suppression technique is applied.

Traumatic pseudoaneurysm in subclavian artery of 38-year-old man. Coronal unenhanced (A) and axial enhanced (B) T2-weighted images show mass (arrows) in region of right subclavian artery compressing brachial plexus. Note concentric rings of varying signal intensities due to clot that forms walls of this pseudoaneurysm.

Charcot-Marie-Tooth disease in 18-year-old woman. Coronal fat-suppressed T2-weighted image shows left brachial plexus to be thick and hyperintense.

Non-Hodgkin lymphoma in a 53-year-old man. Axial (a) and oblique sagittal (b) T1-weighted images show multiple small masses (solid arrows) in the base of the neck and involving the right brachial plexus (arrowheads). Also note the superior mediastinal adenopathy (curved arrow in b). In b, open straight arrow = subclavian artery.

Malignant peripheral nerve sheath tumor (neurosarcoma) of the upper trunk of the brachial plexus.

Neurofibromatosis type 1 (NF1) shows large plexiform neurofibromas of both brachial plexuses, affecting nerve roots C5, C6, C8, T1 and T2.

MRI shows a patient who recently underwent neck surgery. The C5 and C6 nerve roots have been completely severed (neurotmesis) and there is evidence of post-traumatic neuroma formation at their ends. The patient was treated with nerve transfer surgery.

Melanoma in a 35-year-old man. Axial T1- (a) and T2-weighted (b) images show a large mass in the right axilla (solid arrows in a) contiguous to and displacing the right brachial plexus (arrowhead in a). Note the subtle areas of increased T1 signal intensity within the mass that are characteristic of melanoma. Open arrow = subclavian artery.

ConclusionThe brachial plexus can be efficiently imaged and effectively interpreted by the general radiologist when approached from a practical standpoint. Optimization of a practical BP imaging protocol is paramount to identify normal anatomy and associated pathology. Practical and useful information that can help the referring physician include, pre- vs. post-ganglionic location of lesion, mass vs. non-mass like enhancement, laterality or bilateral nature of disease, location of injury/mass/abnormality in BP segments (e.g. root, trunk, division, etc.), and anatomical region and surrounding structures involved (e.g., interscalene space, costoclavicular triangle, relationship to subclavian/axillary vessels).

Thank You.