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The brachial plexus
The Brachial Plexus Suresh K. Mukherji, Mauricio Castillo, and Archana G. Wagle The brachiai plexus arises from the lower cervical and upper thoracic spinal nerve roots. It courses between the anterior and middle scalene muscles and adjacent to the subclavian artery. The brachial plexus may be visualized by both MRi and CT. Symptoms of a brachial plexopathy commonly are nonlocalizing, Traumatic injuries and involvement by tumors probably account for the majority of etiologies responsible for these plexopathies. Inflammatory processes also involve the brachial plexus, This article reviews the anatomy of the brachial plexus from both surgical and radiographic approaches and also addresses the symptomatology of brachial plexopathy underlying it. Copyright © 1996 by W.B. Saunders Company
IAGNOSTIC radiologists often find imaging of the brachial plexus complicated and confusing. This difficulty arises because of the complex anatomy of the brachial plexus and the nonspecific symptoms associated with a brachial plexOpathy that make proper localization of the inciting lesion troublesome. This article (a) reviews the anatomy of brachial plexus with an emphasis on the imaging landmarks that help to identify it, (b) describes the clinical symptoms associated with brachial plexopathies and identifies specific physical examination findings that help to localize the lesion, and (c) reviews the most common pathologies that involve the brachial plexus.
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ANATOMY Classic Anatomy
The brachial plexus originates from the anterior divisions of the spinal nerve roots of C5-T11 (Fig 1). Variations in innervation are present occasionally. A prefixed brachial plexus occurs when C4 replaces T1 as a dominant contributor. Similarly, a postfixed plexus is present when the brachial plexus receives contributions from C6T2. Although the modifications in the innervation of the brachial plexus have been emphasized in the literature, these variations appear to have little clinical significance. The distribution of the innervation to the upper limb follows a similar pattern regardless of the specific roots that comprise the brachial plexus. 1 The brachial plexus is composed of the roots, trunks, divisions, cords, and branches. This successive progression of structures that form the brachial plexus is often difficult to remember. We find the mnemonic, Radiology Techs
Drink Cold Beverages, helpful in remembering the portions of the brachial plexus. 1 The brachial plexus is formed in the majority of individuals by the anterior divisions of the spinal nerves of C5-T1, which form its roots. The roots of the brachial plexus then combine to form the three trunks (upper, middle, and lower). The roots of C5 and C6 combine to form the upper trunk, whereas the roots of C8/T1 combine to form the lower trunk. The C7 root is the sole contributor of the middle trunk. 1,2 The trunks of the brachial plexus then split into anterior and posterior divisions. These divisions combine to form the cords of the brachial plexus. The cords of the brachial plexus are named (posterior, lateral, and medial) according to their relationship to the adjacent subclavian artery. The posterior divisions of the upper, middle, and lower trunks combine to form the posterior cord. The anterior divisions of the upper and middle trunks combine to form the lateral cord, and the anterior division of the lower trunk continues to form the medial cord. 1,2 The brachial plexus terminates in various branches that supply motor and sensory innervation to the upper extremity. The suprascapular nerve is the only terminal branch that originates from a trunk of the brachial plexus. This nerve From the Departments of Radiology, Surgery, and Anesthesiology, University of North Carolina School of Medicine; and The University of North Carolina School of Dentistry, Chapel
mtt, NC. Address reprint requests to Suresh K. Mukherji, MD, Department of Radiology, 3324 Infirmary CB# 7510, University of North Carolina School of Medicine, Chapel Hill, NC 275997510. Copyright © 1996 by FEB. Saunders Company 0887-2171/96/1706-000555. O0/0
Seminars in Ultrasound, CT, andMRI, Vo117, No 6 (December), 1996: pp 519-538
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posterior to the clavicle, adjacent to the subclavian artery. The infraclavicular plexus also courses adjacent to the subclavian artery and contains the cords and portions Of the distal branches of the brachial plexus. 2
RadiographicAnatomy
Fig 1. Normal brachial plexus. Schematic illustration of the normal anatomy of the brachial plexus. (Reprinted with permission. 2)
arises from the upper trunk and supplies the supraspinatus, infraspinatus, and teres major muscles. The posterior cord gives rise to the thoracodorsal (innervating the latissimus dorsi muscle) and subscapular nerves (innervating the subscapularis and teres major muscles) before terminating in the axillary and radial nerves. 2 The lateral pectoral nerve (innervating the pectoralis major muscle) originates from the lateral cord before terminating as the musculocutaneous nerve (innervating the biceps and coracobrachialis muscles) and the lateral cord contribution to the median nerve. 2 The medial cord gives rise to the medial brachial cutaneous, medial antebrachial cutaneous, and medial pectoral nerves (innervating the pectoralis major muscle) before terminating as the ulnar nerve and the medial cord contribution to the median nerve. 2
SurgicalAnatomy The surgical anatomy of this region takes into account the classic anatomy of the brachial plexus in combination with the surrounding anatomic structures. The surgical classification is based on the relationship of the brachial plexus to the clavicle, which it divides into supraclavicular, retroclavicular, and infraclavicular segments. The supraclavicular brachial plexus contains the roots and trunks and is situated in the posterior triangle between the anterior and middle scalene muscles. The retroclavicular plexus contains the divisions and is located
The radiologist thus can identify specific portions of the brachial plexus based on certain anatomic structures that are seen easily On imaging studies. The fascial plane between the anterior and middle scalene muscles contains the roots and cords of the brachial plexus (Fig 2). The divisions and cords course adjacent to the subclavian artery (Figs 3 and 4). Thus, any mass that is adjacent to the subclavian artery is close to the divisions and cords of the brachial plexus. The branches of the brachial plexus are difficult to identify individually on imaging studies. However, it may be safe to assume that a mass in the axillary region probably involves the terminal branches of the cords. CLINICAL CONSIDERATIONS
Clinical features of a brachial plexopathy often are vague and nonspecific. Patients vary in their presentation depending on the extent, degree, and duration of injury. Symptoms include motor, sensory, and, sometimes, autonomic disturbances of the supraclavicular region, shoulder, and upper extremity. These symptoms may be exacerbated by certain arm and shoulder positions. Occasionally, these findings may be associated with tenderness or with a palpable abnormality above the clavicle. 3 Once a patient is thought to have an abnormality involving the brachial plexus, the next step is determining which portion is involved. This determination often is difficult because of the complex nature of the components comprising the brachial plexus. Motor weakness is seen primarily in patients with obstetric-relate d palsies and avulsions of anterior roots. Sensory deficits are more often seen in patients with neoplastic and/or radiation-induced plexopathies. Sensory losses tend to be incomplete and within the territory of the plexus injury. Differentiation between neoplastic and radiationinduced brachial plexopathies may be very difficult based on clinical evaluation alone. In
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Fig2. Normalbrachialplexus. Axial views from (A) an anatomic specimen and (B) a Tl-weighted study show the supraclavicular brachial plexus (arrows) situated between the anterior (A) and middle scalene (M) muscles,
general, neoplastic plexopathies tend to be more painful and progress more rapidly than those induced by radiation. Long-term complications resulting from brachial plexopathies include muscle wasting, upper extremity edema, osteoporosis, joint contractures, complex regional pain syndromes, and/or sympathetically mediated pain, as well as joint degeneration. Permanent lesions also may result in depression/anxiety, financial losses, and inability to work.
There are certain clinical findings that help to localize the inciting lesion and thus permit radiologists to focus their diagnostic evaluation. The phrenic nerve receives contributions from C3-C5. Because of this overlap in innervation with the upper roots of the brachial plexus, a plexopathy associated with a paralyzed diaphragm indicates involvement of the upper plexus. The rhomboid and serratus anterior muscles are innervated by proximal branches of the brachial plexus (C5-C7). Thus, rhomboid
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Fig 3. Normalbrachialplexus. Coronal views from (A) an anatomic and (B) a Tl-weighted image show the relationship of the divisions and cords of the brachial plexus (straight arrows) adjacent to the subclavian artery (curved arrows).
muscle paralysis or winging of the scapula is indicative of a proximal injury. 4 The Erb-Duchene palsy generally is a consequence of birth injury that results from shoulder dystocia during a vertex vaginal delivery. Obstetrical palsies tend to occur more often in larger babies, breech or forceps deliveries, and after prolonged labor. The right shoulder is affected more commonly because the head is usually in a left occiput anterior position. 5 Excessive traction on the head and neck results in an injury limited to the C5 and C6 nerve roots. Patients
with an Erb's palsy have characteristic physical findings: adduction and internal rotation of the arm with pronation of the forearm. 6 Several associated clinical findings implicate a lower brachial plexus lesion. The stellate ganglion receives contributions from C8-T1. Thus, a brachial plexopathy associated with an ipsilateral Horner's syndrome is indicative of a lesion involving the lower brachial plexus. The classic Dejerine-Klumpke palsy is caused by a failure to deliver the upper extremities before the head during a breech vaginal delivery. The
Fig4. Normalbrachialplexus. Sagittal image obtained lateral to the anterior scalene muscle shows the close proximity of the cords of the brachial plexus (arrows) to the subclavian artery (A). V, subclavian vein.
Fig 5. Posttraumatic pseudomeningocele. A myelogram performed in a patient involved in a motor vehicle accident shows the characteristic appearance of a pseudomeningocele (arrow).
Fig 6. Normal nerve roots. CT myelogram (3-mm-slice thickness) performed (in the same patient as in Fig 5) at an uninvolved level shows linear defects in the intrathecal contrast because of the ventral (arrows) and dorsal nerve roots (black arrowheads).
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incidence of the Dejerine-Klumpke palsy has decreased markedly over the last 20 years because of a reduction in the number of vaginal deliveries performed for breech presentation. 7 Forcible abduction of the arms causes excessive stretching and results in an injury to the nerve roots of C7-T1. 6,7 This injury involves the lower plexus, thereby affecting the ulnar-innervated muscles in the hand and forearm, the medianinnervated intrinsic hand muscles, and the radial-innervated extensors. Such an injury characteristically results in a paralyzed ("claw") hand. 5 Because of the overlap in innervation with the stellate ganglion, Klumpke's palsy also may be associated with ipsilateral Homer's syndrome,s Several findings may be indicative of a more severe injury to the brachial plexus. A plexopathy associated with findings similar to those of a Brown-Sequard syndrome may suggest a proximal nerve root avulsion and spinal cord injury.1 A flail limb with complete absence of deep tendon reflexes is indicative of a complete disruption of the brachial plexus. 1 PATHOLOGY
Trauma
The initial imaging evaluation in patents with a posttraumatic brachial plexopathy should consist of plain films of the cervical spine, shoulder, clavicle, and chest. These plain films should be assessed for fractures or subluxations that could account for the acute neurological deficit.
Posttraumatic nerve root avulsion of the brachial plexus results from a forcible trauma that separates the arm from the shoulder. 9,1° This avulsion may result in the stretching and tearing of fibrous attachments that extend from the nerves to their respective transverse processes. Pseudomeningoceles arise from tears of the dura and arachnoid membranes caused by the root sleeves being pulled out into the intervertebral foramen. Nerve root avulsion results if the traction force exceeds the elastic tolerance of the root. 9,1° Spinal cord injury may occur from direct contusion or by avulsion of the nerve root. 9,1° Thus, it is possible to have posttraumatic pseudomeningoceles without a coexistent nerve root avulsion, a1,12 Conversely, approximately 20% of cervical nerve root avulsions are not associated with a pseudomeningocele.13 Both CT myelography and MRI may be used to evaluate patients with posttraumatic brachial plexopathies. The characteristic findings in a posttraumatic brachial plexus stretch injury are pseudomeningoceles, which may be detected by both CT myelography and MRI (Fig 5). Thinsection CT myelography (l-ram-to 3-mm-thick sections) allows for consistent visualization of the ventral and dorsal nerve roots within the spinal canal and thus is the preferred imaging modality (Fig 6). Absence of a nerve root shadow on CT myelography is indicative of nerve root avulsion9 (Fig 7). Nerve root or dural
Fig 7. Pseudomeningocele with nerve root avulsion. CT myelogram (3-mm-slice thickness) performed in the same patient as in Fig 5 shows the absence of the nerve root filling defects on the side of the pseudomeningocele (P). Note the normal ventral (arrow) and dorsal roots (black arrowhead) on the uninvolved side.
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Fig8. MRIof pseudomeningocele. MRI performed in an infant with Erb's palsy, (A) Axial T1weighted image shows a subtle asymmetric loss of fat in the right neural foramina (arrows). (B) The pseudomeningocele is seen readily on gradient-echo sequences (arrow); however, the intraspinal nerves cannot be detected with MRI.
thickening seen on MRI is suggestive of nerve root avulsion or edema. Hong et al 9 have demonstrated recently that CT myelography has a higher sensitivity (83.3% v 72.7%) and specificity (100% v 86.7%) for detecting nerve root avulsion, compared with MRI. Recent technical advances in MRI permit improved visualization of the nerve roots within the spinal canal in normal patients; however, these advanced techniques are limited primarily to tertiary institutions and are not currently in general
use 14-17(Fig 8). MRI does allow visualization of pseudomeningoceles, which do not fill with contrast on CT meylography. The role of MR myelography for evaluating brachial plexus injuries is currently being evaluated.18 Determining the status of the nerve roots within the spinal canal in patients with posttraumatic brachial plexopathy provides important information for the treating clinician. Patients with a posttraumatic plexopathy with intact nerve roots probably will proceed to further
Fig 9. Hematoma. Axial contrast-enhanced CT obtained in a patient involved in a motor vehicle accident shows a hematoma (Hi compressing the left brachial plexus. (Courtesy of Linda Gray, MD, Duke University, Durham, NC.)
Fig 10. Brachial plexopathy caused by vascular compression, (A) Innominate artery angiogram performed in a patient with a right brachial plexopathy after a gunshot wound shows multip e pseudoaneurysms involving the common carotid and subclavian arteries. (B) The patient's Symptoms resolved after stenting of the subclavian artery aneurysm. (Courtesy of Matthew Mauro, MD, University of North Carolina, Chapel Hill, NC.)
Fig 11. Schwannoma. Axial contrast-enhanced CT shows a large schwannoma (large arrows) arising from the brachial plexus. Note the anterior displacement of the anterior scalene muscle (A) and posterior displacement of the middle scalene (M) muscle by the tumor. Compare these features to the normal anatomy present on the uninvolved side. Curved arrow, brachial plexus.
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Fig 12, Schwannoma. (A) Axial, gadolinum-enhanced, T1weighted image shows the mass arising between the anterior (A} and middle (M) scalene muscles, indicating that the lesion is arising from the brachial plexus. (B) Coronal image shows that a component of the mass is extending toward the neural foramina (curved arrow). Note the normal appearance of the brachial plexus on the uninvolved side (straight arrow). (Courtesy of Kent Remley, MD, University of Minnesota, Minneapolis, MN.)
nerve conduction studies to localize the site of injury better. Recent advances in microsurgery permit reconstruction of severed nerve roots using neurotization, nerve grafting, neurorrhaphy, and neurolysis. 9,19-22 Thus, distinguishing supraganglionic nerve root avulsion from infraganglionic injuries provides important information for both patient management and prognosis. 9 Other posttraumatic lesions that may result in a brachial plexopathy include hematomas, vascular compression from pseudoaneurysm formation, and complete disruption of the brachial
plexus (Figs 9 and 10). The presence of intramedullary or extramedullary hematoma may be detected with MRI. MRI is superior to CT for determining the presence and extent of soft tissue injuries.
Neoplasms A variety of neoplasms may involve the brachial plexus. These lesions may be classified as tumors of neural (primary) or nonneural (secondary) origin. Primary brachial plexus tumors most commonly arise from the nerve sheaths. The most Common benign neural tumors are
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neurofibromas and schwannomas. Neurofibromas are the most common neural tumor to involve the brachial plexus. Histologically, these lesions are unencapsu!ated tumors believed to arise from the nerve fascicles. 3 One third of these lesions occur in patients with neurofibromatosis type 1 (NF-1), whereas two thirds of CaSes are sporadic. Neurofibromas arising in patients with NF-1 occur with equal incidence in males and females. These tumors are characteristically multiple and plexiform in appearance with diffuse involvement of the brachial plexus. In contrast, sporadic neurofibromas are seen more commonly in females (2:1 to 3:1 female-to-male ratio). Sporadic neur0fibromas typically are solitary and probably originate in the supraclavicular brachial plexus. 3 Schwannomas are the second most common neural tumor involving the brachial plexus. Histologically, these lesions are encapsulated, thereby often permitting surgical excision without sacrificing the adjacent nerves. The majority of schwannomas are solitary, and they are slightly more common in the upper brachial plexus. 3 The imaging features of solitary neurofibromas are essentially indistinguishable from those of schwannomas. On CT, these lesions have attenuation similar to that of muscle, and they enhance variably with contrast (Fig 11). Both tumors may be associated with bony remodel-
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ing. On MRI, these two lesions are isointense to muscle on Tl-weighted sequences and hyperi ntense on T2-weighted sequences. Both tumors typically enhance after intravenous gadolinium administration (Fig 12). The diagnosis of neurofibroma may be made with a high degree of confidence if the lesions tiave a plexiform appearance or occur in a patient with NF-12,23 (Figs 13-15). Malignant neural tumors are very rare and consist mostly of fibrosarcomas 3,24,25and neurogenic sarcomas (malignant neurofibromas). These lesions occur most commonly in patients with neurofibromatosis type 1, especially after radiation therapy. 3,26 The imaging features of malignant neural tumors are similar to those of their benign counterparts, thus making it difficultto differentiate benign from malignant processes based on a single imaging study (Fig 16). The diagnosis of a malignant nerve sheath tumor may be suggested by a progressively enlarging mass in a patient with NF-1. Secondary neoplasms may extend to involve the adjacent brachial Plexus. These lesions may be either benign or malignant. Benign masses that involve the brachial plexus include lipoma, lipoblastoma, desmoid, lymphangioma, myoblastoma, osteochondroma, and ganglioneuroma 24,25 (Fig 17). Malignant neoplasms that may involve the
Fig 13. Plexiform neurofibroma. Axial gadolinium-enhanced Tl-weighted study performed in a patient with neurofibromatosis type I shows the characteristic appearance of plexiform neurofibromas.
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Fig 14. Piexiform neurofibroma. Axial T2-weighted image obtained in a patient with neurofibromatosis type I shows multiple high.signal masses situated between the anterior (A) and middle (M) scalene muscles. This location indicates that these neurofibromas are arising from the brachial plexus,
brachial plexus commonly result from direct extension from a Pancoast's tumor or because of metastatic disease. Involvement of the brachial plexus by direct extension of a Pancoast's tumor may be suspected in patients who present with supraclavicular pain, weakness, and paresthesias. Long-standing involvement may result in muscle wasting, z7 Imaging findings suggestive of brachial plexus invasion by a superior sulcus tumor are obliteration of the apical fat and proximity of the mass to the brachial plexus (Fig
18). Tumors that have been reported to metastasize to the brachial plexus include breast, lymphoma, bladder, gastrointestinal, testicular, thyroid, lung, melanoma, head and neck, and sarcomas 24,25(Figs 19 and 20). The imaging modality of choice in patients with possible neoplastic invasion of the brachial plexus is MRI because of its multiplanar capability and high soft tissue characterization. Previous studies have shown MRI to have a high sensitivity (100%) in detecting neoplastic in-
Fig 15. Plexiform neurofibroma. Noncontrast Tl-weighted study performed in a patient with neurofibromatosis type I shows multiple piexiform neurofibromas. The encasement of the subclavian artery (curved arrow) by these lesions indicates that the brachial plexus is involved by this process,
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Fig 16 Neurofibrosarcoma. (A) Axial, gadolinium-enhanced, Tl-weighted image shows a neurofibrosarcoma (T) situated anterior to the middle scalene muscle (M) and adjacent to the subclavian artery (A). (B) Sagittal, gadolinium-enhanced, Tl-weighted image shows the tumor (T) adjacent to the subclavian artery (A) and in the expected position of the brachial plexus. (Compare with Fig 4.)
volvement of the brachial plexus. 28 The extent of disease also is depicted better with MRI than with CT. 29 Coronal Tl-weighted images are especially helpful for assessing the status of the apical fat in patients with Pancoast's tumors and for evaluating the relationship of masses to the brachial plexus.
Inflammatory Processes Inflammatory processes that may involve the brachial plexus include radiation therapy, neuri-
tis, and infections. Radiation therapy (RT) may injure the brachial plexus and cause a plexopathy. Three classic syndromes of RT-induced brachial plexopathy have been described. The most common form is a delayed progressive radiation fibrosis. 3°-32 The remaining two forms of radiation damage are a reversible or transient plexopathy 3°,33 and an acute ischemic plexopathy.30, 34 Radiation-induced brachial plexopathy is the most common and most severe peripheral ner-
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Fig 16. (cont'd.} (C) Axial, fatsaturated, Tl-weighted image shows abnormal enhancement along the supraclavicular position of the brachial plexus (curved arrow}, suggestive of perineural extension. A, anterior scalene muscle; M, middle scalene muscle. (D) Sagittal, fat-saturated, gadolinium-enhanced, T1weighted image obtained at the level of the neural foramina shows abnormal enhancement of the C7 and C8 nerve roots (straight arrows}, suggestive of perineural extension. Compare this with the normal appearance of the T1 nerve root (curved arrow). These findings were con. firmed at surgery.
vous system complication of RT. Radiation damage to the brachial plexus appears to be dose related and most likely occurs in patients who have received doses in excess of 6,000 cGy. 35 This damage is seen most commonly in women who have been treated with R T for breast cancer. The plexopathy tends to be delayed and progressive with the majority of
patients presenting at least 6 months after the completion of RT. The initial symptoms include paresthesias, followed by pain and weakness. These symptoms typically occur in an upper trunk distribution with weakness of the arm flexors and shoulder abduction. 36 Pain can accompany these paresthesias, but it usually occurs late in the course of this syndrome. 35
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Fig 17. Lipoma. (A) Coronal Tl-weighted image shows a lipoma arising from the left supraclavicular region. (B) Axial T1weighted image shows that the lipoma surrounds the cords of the brachial plexus (arrows),
However, other reports suggest that RT-induced plexopathies are generalized and that the distribution of the deficits is not helpful in differentiating this variety of plexopathy from a neoplastic one. 3 Histologically, in RT-induced plexopathy, there is dense fibrous tissue encasing the brachial plexus with wallerian degeneration. 37 On physical examination, radiationinduced brachial plexopathy may result in reflex abnormalities, intrinsic muscle weakness, muscle atrophy, and lymphedema.
MRI is the modality of choice for evaluating patients previously treated with RT to the supraclavicular region. 38,39The imaging findings of RT-induced brachial plexopathy are diffuse thickening and enhancement of the brachial plexus without a focal mass 2,3° (Fig 21). The presence of a focal mass in a patient treated with RT is suspicious for recurrent tumor and requires further evaluation, especially in patients treated with doses of less than 6,000 cGy. Horner's syndrome is caused rarely by RT alone
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Fig 18. Pancoast's tumor. (A) Coronal, noncontrast, Tl-weighted image shows a left superior sulcus tumor (T) that has extended into the subpleural fat and has invaded the lower trunk of the brachial plexus. The black arrowheads denote the C8 and T1 roots before formation of the lower trunk. (B) Sagittal, noncontrast, T1-weighted image shows that the mass has invaded the lung apex and encased the lower trunk of the brachial plexus, Not e the normal appearance of the upper and middle trunks of the brachial plexus (black arrowheads).
and, when present, also strongly suggests recurrent tumor. Active inflammation of the brachial plexus is termed brachial neuritis. Its etiology may be a primary viral infection (eg, cytomegalovirus, coxsackie) or a complication from prior infection. Brachial neuritis also may result as a complication of the previous administration of a serum vaccine, antibiotic, or other drug. Idiopathic and heredofamilial forms of brachial neuritis also have been described. 37 Patients with brachial neuritis typically present between
the third and seventh decades of life. The condition is slightly more common in males than in females (2.4:1). Clinically, these patients present with an ache in the supraclavicular region and shoulder. The pain often worsens over a 3- to 10-day period and may be followed by weakness and sensory and reflex impairment: In most cases, the disease is self-limited and subsides over a 6- to 12-week period. However, residual deficits occur in some patients. 37 MRI is the modality of choice in patients suspected of having brachial neuritis. The MRI findings are
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Fig 19, Breast metastases. Noncontrast, coronal, Tl-weightjed study performed in a patient previously treated for breast Carcinoma who presented with a left brachial plexopathy. The study shows a mass in the left supraclavicular region (large arrow). The fact that the mass surrounds the subclavian artery (small arrow) suggests that the mass involves the brachial plexus.
diffuse thickening, abnormal T2-weighted signal intensity, and abnormal enhancement of the brachial plexus on gad01inium-enhanced images 2 (Fig 22). Infectious processes involving the brachial plexus most commonly involve its supragangli0nic portion and typically are caused by discitis with associated epidural abscesses. Involvement of the more distal components of the brachial
Fig 20. Squamous cell carcinoma metastases. Noncontrast, coronal, Tl-weighted study performed in a patient with metastatic squamous cell carcinoma who presented with pain and weakness in the left arm, The study shows a large mass (curved arrow) encasing the subclavian artery (a), indicative of brachial plexus involvement. Note the normal appearance of the cords of the brachial plexus (straight arrows) and their relationship to the subclavian artery (a) on the uninvolved side.
plexus is unusual and may be caused by extension from an adjacent infection. Miscellaneous Causes
The clinical symptoms Of degenerative cervical disk disease may mimic those of a brachial plexopathy; therefore, evaluation of the cervical spine should be included in imaging studies of the brachial plexus. Eighty Percent to ninety
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Fig 21, Radiation-induced brachial plexopathy, (A) Coronal, noncontrast, T1-weighted image obtained in patient with breast carcinoma treated with radical mastectomy and 6,000 cGy of radiation who presented 1 year after RT with tingling in the fingers of the left hand, The study shows diffuse thickening of the brachial plexus (arrows) without evidence of a focal mass, (B) Sagittal, noncontrast, Tl-weighted image shows thickening of the cords of the brachial plexus (arrows). Biop* sies of this region showed fibrosis without evidence of tumor, a, subclavian artery. (Courtesy of Pamela Van Tassel, MD, Medical University of South Carolina, Charleston, SC,)
percent of cervical radiculopathies involve the C6 (C5/C6 disk) and C7 (C6/C7 disk) roots. Patients may Present with numbness, pain, sensory loss, and diminished reflexes at the affected levels. These symptoms may be exacerbated by
Fig 22. Idiopathic brachial neuritis. Axial T2-weighted image in a patient with biopsyproven hypertrophic interstitial neuritis of the brachial plexus shows fusiform enlargement and abnormal increased signal of the brachiai plexus (arrows), A, anterior scalene muscle; M, middle scalene muscle, (Courtesy of Kent Remley. MD~ University of Minnesota, Minneapolis, MN,)
coughing, sneezing, or lateral head movements. 23 Brachial plexopathy also may be caused by cervical ribs. Cervical ribs are present in approximately 1% of the population and are symptom-
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Fig 23. CT-guided neurolysis of the brachial plexus. This 70year-old man with metastatic squamous cell carcinoma involving the left brachial plexus and chest wall presented with left upper extremity paralysis and severe pain that was poorly controlled on high-dose analgesic therapy. (A) Axial CT image shows that the tip of a 20-gauge needle has been advanced between the plane of the anterior (a) and middle (m) scalene muscles and thus is in the expected location of the supraclavicular brachial plexus. (B) CT performed after administration of a mixture of Contrast material and alcohol. The study Shows that the mixture is extending along the expected location of the brachial plexus; After the procedure, the patient had a significant reduction in pain and was able to reduce his analgesic medication by 50%.
atic in 10% of affected individuals. 23,4°They are more common in females than in males (2:1) and are unilateral in 50% to 80% of individuals. Occasionally, a cervical rib may be attached to the first rib by a fibrous band. The brachial plexus may be affected by cervical ribs in one of two way s . The cervical rib may be positioned so that the brachial plexus must cross over it to enter the axilla, thereby stretching the lower trunk. Second, t h e cervical rib may narrow the space between the posterior aspect of the first
rib and the anterior scalene muscle, thus reducing the area through which the brachial plexus and subclavian artery course.Z3 ,4°,4l The cervical rib syndrome is believed to result from compression of the lower trunk of the brachial plexus as it crosses over the cervical rib or by compression of the lower trunk by a fibrous band that attaches to the first rib. This syndrome is more common in females. The symptoms consist of pain a n d / o r parasthesias along the ulnar border of the forearm and hand and motor weakness in
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a similar distribution. Continued compression may result in muscle wasting that initially involves the thenar eminence but may also spread to involve the small muscles of the hand. 23,42 BRACHIAL PLEXUS INTERVENTION
A variety of interventional procedures can be performed on the brachial plexus using CT guidance. 43,44Percutaneous biopsies of indeterminate masses adjacent to the brachial plexus may be performed safely in patients with previously treated malignancies, thereby avoiding the need for open surgery. 43 CT also may be used for needle localization for prognostic nerve
root blocks in patients with a mononeuropathy caused by for aminal stenosis. 44 Phenol neurolysis of the brachial plexus using CT-guided needle localization may be performed in patients with intractable plexopathy from advanced metastatic disease 42 (Fig 23). CT guidance provides more accurate needle localization, especially in patients with anatomy that has been distorted by tumor extension. By combining the ablative agent with contrast material, the extent of the neurolysis can be visualized with CT. These procedures are reserved for patients whose pain has been poorly controlled with high doses of analgesic medication. 4z
REFERENCES 1. Guha A, Graham B, Kline DG, Hudson AR: Brachial plexus injuries, in Wilkins RH, Rengachary SS (eds): Neurosurgery (ed 2). New York, NY, McGraw-Hill, 1996, pp 3121-3134 2. Posniak HV, Olson MC, Dudiak CM, et al: MR imaging of the brachial plexus. A JR Am J Roentgenol 161:373-379, 1993 3. England JD, Summer AJ: Nontraumatic brachial plexopathy, in Wilkins RH, Rengachary SS (eds): Neurosurgery (ed 2). New York, NY, McGraw-Hill, 1996, pp 32453250 4. Kline DG, Hudson AR: Acute injuries of peripheral nerves, in Youmans JR (ed): Neurological Surgery (ed 4). Philadelphia, PA, 8aunders, 1996, pp 2103-2181 5. Boome RS, Kaye JC: Obstetrical traction injuries of the brachial plexus. J Bone Joint Surg 70B:571-576, 1988 6. Behrman RE: The fetus and the neonatal infant, in Behrman RE, Kliegman RM, Nelson WE, et al (eds): Nelson Textbook of Pediatrics (ed 14). Philadelphia, PA, Saunders, 1992, pp 421-524 7. Al-Quattan MM, Clarke HM, Curtis CG: Klumpke's birth palsy: Does it really exist? J Hand Surg 20:19-23, 1995 8. Cunningham FG, MacDonald PC, Gant NF, et al: Lie, presentation, attitude, and position of fetus, in Williams Obstetrics (ed 19). Norwalk, CT, Appleton & Lange, 1993, p. 276 9. Hong SH, Chan KH, Han MH, et al: Cervical root avulsion: Magnetic resonance imaging findings and comparison of diagnostic accuracy between magnetic resonance imaging and conventional myelography. Int J Neuroradiol 2:182-187, 1996 10. Shapiro R: Myelography (ed 3). Chicago, IL, Year Book Medical, 1975, pp 195-224 11. Davies ER, Sutton D, Bligh AS: Myelography in brachial plexus injury. Br J Radiol 39:362-371, 1966 12. Kewalramani LS, Taylor RG: Brachial plexus avulsion: Role of myelography. J Trauma 15:603-608, 1975 13. Hashimoto T, Mitomo M, Hirabuki N, et al: Nerve root avulsion of birth palsy: Comparison of myelography with CT myelography and somatosensory evoked potential. Radiology 178:841-845, 1991
14. Francel PC, Koby M, Park TS, et al: Fast spin echo magnetic resonance imaging for radiological assessment of neonatal brachial plexus injury. J Neurosurg 83:461-466, 1995 15. Schmalbrock P, Brogan M, Cbakeres DW, et al: Optimization of submillimeter resolution MR imaging methods for the inner ear. J Magn Reson Imaging 3:451-459, 1993 16. Schmalbrock P, Pruski J, Sun L, et al: Phased array RF coils for high resolution imaging of the inner ear and brainstem. J Comput Assist Tomogr 19:11-14, 1995 17. Ying K, Schmalbrock P, Clymer BD: Echo-time reduction for submillimeter resolution imaging with a phase encoded time reduced acquisition method. Magn Reson Med 33:82-87, 1995 18. E1-Gammel T, Brooks BS, Freedy RM, Crews CC: MR myelography: Imaging findings. AJR Am J Roentgenol 164:173-177, 1995 19. Carlstedt TP: Spinal nerve root injuries in brachial plexus lesions: Basic science and clinical applications of new surgical strategies. A review. Microsurgery 16:13-16, 1995 20. Glasby MA, Helms TE: Repairing spinal roots after brachial plexus injuries. Paraplegia 33:359-361, 1995 21. Gu YD, Zhang GM, Chen DS: Cervical nerve root transfer from contralateral normal side for the treatment of brachial plexus root avulsions. Chin Med J (Engl) 104:209211, 1991 22. Yamada S, Peterson GW, Soloniuk DS, Will AD: Coaptation of the anterior rami of C3 and C4 to the upper trunk of the brachial plexus for cervical nerve root avulsion. J Neurosurg 75:667-668, 1991 23. Reede DL: Brachial plexus, in Som PM, Curtin HD (eds)! Head and Neck Imaging (ed 3). St. Louis, MO, Mosby Year Book, 1996, pp 976-992 24. Dart LH, MacCarty CS, Love JG, et al: Neoplasms of the brachial plexus. Minn Med 53:959-964, 1970 25. Lusk MD, Kline DG, Garcia CA: Tumors of the brachial plexus. Neurosurgery 21:439-453, 1987 26. Foley KM, Woodruff JM, Ellis FT, et al: Radiationinduced malignant and atypical peripheral nerve sheath tumors. Ann Neurol 7:311-318, 1980
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27. Bagley FH, Walsh JW, Cady B: Carcinomatous versus radiation-induced brachial plexus neuropathy in breast cancer. Cancer 41:2154-2157, 1978 28. Castango AA, Shuman WP: MR imaging in clinically suspected brachial plexus tumor. AJR Am J Roentgenol 149:1219-1222, 1987 29. Rapoport S, Blair DN, McCarthy SM, et al: Brachial plexus: Correlation of MR imaging with CT and pathologic findings. Radiology 167:161-165, 1988 30. Bowen BC, Verma A, Brandon AH, Fiedler JA: Radiation induced brachial plexopathy: MR imaging with clinical correlation. AJNR Am J Neuroradiol (in press) 31. Stoll BA, Andrews JT: Radiation-induced peripheral neuropathy. BMJ 1:834-837, 1966 32. Maruyama Y, Mylrea MM, Logotheis J: Neuropathy following irradiation. AJR Am J Roentgenol 101:216-219, 1967 33. Salner AL, Botnick LE, Herzog AG, et al: Reversible brachial plexopathy following primary radiation therapy for breast cancer. Cancer Treat Rep 65:797-802, 1981 34. Gerard JM, Franck N, Moussa Z, et al: Acute ischemic brachial plexus neuropathy following radiation therapy. Neurology 39:450-451, 1989 35. Kori SH, Foley KM, Posner: Brachial plexus lesions in patients with cancer: 100 cases. Neurology 31:45-50, 1981 36. Wilburn AJ: Brachial plexus, in Dyck PJ, Thomas PK
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(eds): Peripheral Neuropathy (ed 3). Philadelphia, PA, Saunders, 1993, pp 911-950 37. Adams RD, Victor M: Diseases of the peripheral nerves, in Principles of Neurology (ed 5). New York, NY, McGraw-Hill, 1993, pp 1117-1169 38. Iyer RB, Fenstermacher MJ, Libshitz HI: MR imaging of the treated brachial plexus. AJR Am J Roentgenol 167:225-229, 1996 39. Van Es HW, Witkamp TD, Ramos UMP, et al: MR imaging of the brachial plexus using a Tl-weighted threedimensional volume acquisition. Int J Neuroradiol 2:264273, 1996 40. Hollingshead WH: Anatomy for Surgeons, vol 1. The Head and Neck. New York, NY, Harper Row, 1968 41. Armington WG, Harnsberger HR, Osborn AG, Seay AR: Radiographic evaluation of brachial plexopathy. AJNR Am J Neuroradiol 8:361-367, 1987 42. Perkins GD, Rose FC, Blackwood W, et al: Atlas of Clinical Neurology. Philadelphia, PA, Lippincott, 1986 43. Quint D J, Allen RA, Murphy KP: Pereutaneous biopsy of brachial plexus lesions. American Society of Head and Neck Radiology, Los Angeles, CA, April 1996 (abstr) 44. Wagle AG, Mukherji SK, Dogra S: Nerve root blocks and high resolution imaging. 22nd Gulf Atlantic Anesthesia Resident Conference, Tampa, FL, April 1996
IAGNOSTIC radiologists often find imaging of the brachial plexus complicated and confusing. This difficulty arises because of the complex anatomy of the brachial plexus and the nonspecific symptoms associated with a brachial plexOpathy that make proper localization of the inciting lesion troublesome. This article (a) reviews the anatomy of brachial plexus with an emphasis on the imaging landmarks that help to identify it, (b) describes the clinical symptoms associated with brachial plexopathies and identifies specific physical examination findings that help to localize the lesion, and (c) reviews the most common pathologies that involve the brachial plexus.
D
ANATOMY Classic Anatomy
The brachial plexus originates from the anterior divisions of the spinal nerve roots of C5-T11 (Fig 1). Variations in innervation are present occasionally. A prefixed brachial plexus occurs when C4 replaces T1 as a dominant contributor. Similarly, a postfixed plexus is present when the brachial plexus receives contributions from C6T2. Although the modifications in the innervation of the brachial plexus have been emphasized in the literature, these variations appear to have little clinical significance. The distribution of the innervation to the upper limb follows a similar pattern regardless of the specific roots that comprise the brachial plexus. 1 The brachial plexus is composed of the roots, trunks, divisions, cords, and branches. This successive progression of structures that form the brachial plexus is often difficult to remember. We find the mnemonic, Radiology Techs
Drink Cold Beverages, helpful in remembering the portions of the brachial plexus. 1 The brachial plexus is formed in the majority of individuals by the anterior divisions of the spinal nerves of C5-T1, which form its roots. The roots of the brachial plexus then combine to form the three trunks (upper, middle, and lower). The roots of C5 and C6 combine to form the upper trunk, whereas the roots of C8/T1 combine to form the lower trunk. The C7 root is the sole contributor of the middle trunk. 1,2 The trunks of the brachial plexus then split into anterior and posterior divisions. These divisions combine to form the cords of the brachial plexus. The cords of the brachial plexus are named (posterior, lateral, and medial) according to their relationship to the adjacent subclavian artery. The posterior divisions of the upper, middle, and lower trunks combine to form the posterior cord. The anterior divisions of the upper and middle trunks combine to form the lateral cord, and the anterior division of the lower trunk continues to form the medial cord. 1,2 The brachial plexus terminates in various branches that supply motor and sensory innervation to the upper extremity. The suprascapular nerve is the only terminal branch that originates from a trunk of the brachial plexus. This nerve From the Departments of Radiology, Surgery, and Anesthesiology, University of North Carolina School of Medicine; and The University of North Carolina School of Dentistry, Chapel
mtt, NC. Address reprint requests to Suresh K. Mukherji, MD, Department of Radiology, 3324 Infirmary CB# 7510, University of North Carolina School of Medicine, Chapel Hill, NC 275997510. Copyright © 1996 by FEB. Saunders Company 0887-2171/96/1706-000555. O0/0
Seminars in Ultrasound, CT, andMRI, Vo117, No 6 (December), 1996: pp 519-538
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posterior to the clavicle, adjacent to the subclavian artery. The infraclavicular plexus also courses adjacent to the subclavian artery and contains the cords and portions Of the distal branches of the brachial plexus. 2
RadiographicAnatomy
Fig 1. Normal brachial plexus. Schematic illustration of the normal anatomy of the brachial plexus. (Reprinted with permission. 2)
arises from the upper trunk and supplies the supraspinatus, infraspinatus, and teres major muscles. The posterior cord gives rise to the thoracodorsal (innervating the latissimus dorsi muscle) and subscapular nerves (innervating the subscapularis and teres major muscles) before terminating in the axillary and radial nerves. 2 The lateral pectoral nerve (innervating the pectoralis major muscle) originates from the lateral cord before terminating as the musculocutaneous nerve (innervating the biceps and coracobrachialis muscles) and the lateral cord contribution to the median nerve. 2 The medial cord gives rise to the medial brachial cutaneous, medial antebrachial cutaneous, and medial pectoral nerves (innervating the pectoralis major muscle) before terminating as the ulnar nerve and the medial cord contribution to the median nerve. 2
SurgicalAnatomy The surgical anatomy of this region takes into account the classic anatomy of the brachial plexus in combination with the surrounding anatomic structures. The surgical classification is based on the relationship of the brachial plexus to the clavicle, which it divides into supraclavicular, retroclavicular, and infraclavicular segments. The supraclavicular brachial plexus contains the roots and trunks and is situated in the posterior triangle between the anterior and middle scalene muscles. The retroclavicular plexus contains the divisions and is located
The radiologist thus can identify specific portions of the brachial plexus based on certain anatomic structures that are seen easily On imaging studies. The fascial plane between the anterior and middle scalene muscles contains the roots and cords of the brachial plexus (Fig 2). The divisions and cords course adjacent to the subclavian artery (Figs 3 and 4). Thus, any mass that is adjacent to the subclavian artery is close to the divisions and cords of the brachial plexus. The branches of the brachial plexus are difficult to identify individually on imaging studies. However, it may be safe to assume that a mass in the axillary region probably involves the terminal branches of the cords. CLINICAL CONSIDERATIONS
Clinical features of a brachial plexopathy often are vague and nonspecific. Patients vary in their presentation depending on the extent, degree, and duration of injury. Symptoms include motor, sensory, and, sometimes, autonomic disturbances of the supraclavicular region, shoulder, and upper extremity. These symptoms may be exacerbated by certain arm and shoulder positions. Occasionally, these findings may be associated with tenderness or with a palpable abnormality above the clavicle. 3 Once a patient is thought to have an abnormality involving the brachial plexus, the next step is determining which portion is involved. This determination often is difficult because of the complex nature of the components comprising the brachial plexus. Motor weakness is seen primarily in patients with obstetric-relate d palsies and avulsions of anterior roots. Sensory deficits are more often seen in patients with neoplastic and/or radiation-induced plexopathies. Sensory losses tend to be incomplete and within the territory of the plexus injury. Differentiation between neoplastic and radiationinduced brachial plexopathies may be very difficult based on clinical evaluation alone. In
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Fig2. Normalbrachialplexus. Axial views from (A) an anatomic specimen and (B) a Tl-weighted study show the supraclavicular brachial plexus (arrows) situated between the anterior (A) and middle scalene (M) muscles,
general, neoplastic plexopathies tend to be more painful and progress more rapidly than those induced by radiation. Long-term complications resulting from brachial plexopathies include muscle wasting, upper extremity edema, osteoporosis, joint contractures, complex regional pain syndromes, and/or sympathetically mediated pain, as well as joint degeneration. Permanent lesions also may result in depression/anxiety, financial losses, and inability to work.
There are certain clinical findings that help to localize the inciting lesion and thus permit radiologists to focus their diagnostic evaluation. The phrenic nerve receives contributions from C3-C5. Because of this overlap in innervation with the upper roots of the brachial plexus, a plexopathy associated with a paralyzed diaphragm indicates involvement of the upper plexus. The rhomboid and serratus anterior muscles are innervated by proximal branches of the brachial plexus (C5-C7). Thus, rhomboid
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Fig 3. Normalbrachialplexus. Coronal views from (A) an anatomic and (B) a Tl-weighted image show the relationship of the divisions and cords of the brachial plexus (straight arrows) adjacent to the subclavian artery (curved arrows).
muscle paralysis or winging of the scapula is indicative of a proximal injury. 4 The Erb-Duchene palsy generally is a consequence of birth injury that results from shoulder dystocia during a vertex vaginal delivery. Obstetrical palsies tend to occur more often in larger babies, breech or forceps deliveries, and after prolonged labor. The right shoulder is affected more commonly because the head is usually in a left occiput anterior position. 5 Excessive traction on the head and neck results in an injury limited to the C5 and C6 nerve roots. Patients
with an Erb's palsy have characteristic physical findings: adduction and internal rotation of the arm with pronation of the forearm. 6 Several associated clinical findings implicate a lower brachial plexus lesion. The stellate ganglion receives contributions from C8-T1. Thus, a brachial plexopathy associated with an ipsilateral Horner's syndrome is indicative of a lesion involving the lower brachial plexus. The classic Dejerine-Klumpke palsy is caused by a failure to deliver the upper extremities before the head during a breech vaginal delivery. The
Fig4. Normalbrachialplexus. Sagittal image obtained lateral to the anterior scalene muscle shows the close proximity of the cords of the brachial plexus (arrows) to the subclavian artery (A). V, subclavian vein.
Fig 5. Posttraumatic pseudomeningocele. A myelogram performed in a patient involved in a motor vehicle accident shows the characteristic appearance of a pseudomeningocele (arrow).
Fig 6. Normal nerve roots. CT myelogram (3-mm-slice thickness) performed (in the same patient as in Fig 5) at an uninvolved level shows linear defects in the intrathecal contrast because of the ventral (arrows) and dorsal nerve roots (black arrowheads).
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MUKHERJI, CASTILLO, AND WAGLE
incidence of the Dejerine-Klumpke palsy has decreased markedly over the last 20 years because of a reduction in the number of vaginal deliveries performed for breech presentation. 7 Forcible abduction of the arms causes excessive stretching and results in an injury to the nerve roots of C7-T1. 6,7 This injury involves the lower plexus, thereby affecting the ulnar-innervated muscles in the hand and forearm, the medianinnervated intrinsic hand muscles, and the radial-innervated extensors. Such an injury characteristically results in a paralyzed ("claw") hand. 5 Because of the overlap in innervation with the stellate ganglion, Klumpke's palsy also may be associated with ipsilateral Homer's syndrome,s Several findings may be indicative of a more severe injury to the brachial plexus. A plexopathy associated with findings similar to those of a Brown-Sequard syndrome may suggest a proximal nerve root avulsion and spinal cord injury.1 A flail limb with complete absence of deep tendon reflexes is indicative of a complete disruption of the brachial plexus. 1 PATHOLOGY
Trauma
The initial imaging evaluation in patents with a posttraumatic brachial plexopathy should consist of plain films of the cervical spine, shoulder, clavicle, and chest. These plain films should be assessed for fractures or subluxations that could account for the acute neurological deficit.
Posttraumatic nerve root avulsion of the brachial plexus results from a forcible trauma that separates the arm from the shoulder. 9,1° This avulsion may result in the stretching and tearing of fibrous attachments that extend from the nerves to their respective transverse processes. Pseudomeningoceles arise from tears of the dura and arachnoid membranes caused by the root sleeves being pulled out into the intervertebral foramen. Nerve root avulsion results if the traction force exceeds the elastic tolerance of the root. 9,1° Spinal cord injury may occur from direct contusion or by avulsion of the nerve root. 9,1° Thus, it is possible to have posttraumatic pseudomeningoceles without a coexistent nerve root avulsion, a1,12 Conversely, approximately 20% of cervical nerve root avulsions are not associated with a pseudomeningocele.13 Both CT myelography and MRI may be used to evaluate patients with posttraumatic brachial plexopathies. The characteristic findings in a posttraumatic brachial plexus stretch injury are pseudomeningoceles, which may be detected by both CT myelography and MRI (Fig 5). Thinsection CT myelography (l-ram-to 3-mm-thick sections) allows for consistent visualization of the ventral and dorsal nerve roots within the spinal canal and thus is the preferred imaging modality (Fig 6). Absence of a nerve root shadow on CT myelography is indicative of nerve root avulsion9 (Fig 7). Nerve root or dural
Fig 7. Pseudomeningocele with nerve root avulsion. CT myelogram (3-mm-slice thickness) performed in the same patient as in Fig 5 shows the absence of the nerve root filling defects on the side of the pseudomeningocele (P). Note the normal ventral (arrow) and dorsal roots (black arrowhead) on the uninvolved side.
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Fig8. MRIof pseudomeningocele. MRI performed in an infant with Erb's palsy, (A) Axial T1weighted image shows a subtle asymmetric loss of fat in the right neural foramina (arrows). (B) The pseudomeningocele is seen readily on gradient-echo sequences (arrow); however, the intraspinal nerves cannot be detected with MRI.
thickening seen on MRI is suggestive of nerve root avulsion or edema. Hong et al 9 have demonstrated recently that CT myelography has a higher sensitivity (83.3% v 72.7%) and specificity (100% v 86.7%) for detecting nerve root avulsion, compared with MRI. Recent technical advances in MRI permit improved visualization of the nerve roots within the spinal canal in normal patients; however, these advanced techniques are limited primarily to tertiary institutions and are not currently in general
use 14-17(Fig 8). MRI does allow visualization of pseudomeningoceles, which do not fill with contrast on CT meylography. The role of MR myelography for evaluating brachial plexus injuries is currently being evaluated.18 Determining the status of the nerve roots within the spinal canal in patients with posttraumatic brachial plexopathy provides important information for the treating clinician. Patients with a posttraumatic plexopathy with intact nerve roots probably will proceed to further
Fig 9. Hematoma. Axial contrast-enhanced CT obtained in a patient involved in a motor vehicle accident shows a hematoma (Hi compressing the left brachial plexus. (Courtesy of Linda Gray, MD, Duke University, Durham, NC.)
Fig 10. Brachial plexopathy caused by vascular compression, (A) Innominate artery angiogram performed in a patient with a right brachial plexopathy after a gunshot wound shows multip e pseudoaneurysms involving the common carotid and subclavian arteries. (B) The patient's Symptoms resolved after stenting of the subclavian artery aneurysm. (Courtesy of Matthew Mauro, MD, University of North Carolina, Chapel Hill, NC.)
Fig 11. Schwannoma. Axial contrast-enhanced CT shows a large schwannoma (large arrows) arising from the brachial plexus. Note the anterior displacement of the anterior scalene muscle (A) and posterior displacement of the middle scalene (M) muscle by the tumor. Compare these features to the normal anatomy present on the uninvolved side. Curved arrow, brachial plexus.
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Fig 12, Schwannoma. (A) Axial, gadolinum-enhanced, T1weighted image shows the mass arising between the anterior (A} and middle (M) scalene muscles, indicating that the lesion is arising from the brachial plexus. (B) Coronal image shows that a component of the mass is extending toward the neural foramina (curved arrow). Note the normal appearance of the brachial plexus on the uninvolved side (straight arrow). (Courtesy of Kent Remley, MD, University of Minnesota, Minneapolis, MN.)
nerve conduction studies to localize the site of injury better. Recent advances in microsurgery permit reconstruction of severed nerve roots using neurotization, nerve grafting, neurorrhaphy, and neurolysis. 9,19-22 Thus, distinguishing supraganglionic nerve root avulsion from infraganglionic injuries provides important information for both patient management and prognosis. 9 Other posttraumatic lesions that may result in a brachial plexopathy include hematomas, vascular compression from pseudoaneurysm formation, and complete disruption of the brachial
plexus (Figs 9 and 10). The presence of intramedullary or extramedullary hematoma may be detected with MRI. MRI is superior to CT for determining the presence and extent of soft tissue injuries.
Neoplasms A variety of neoplasms may involve the brachial plexus. These lesions may be classified as tumors of neural (primary) or nonneural (secondary) origin. Primary brachial plexus tumors most commonly arise from the nerve sheaths. The most Common benign neural tumors are
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neurofibromas and schwannomas. Neurofibromas are the most common neural tumor to involve the brachial plexus. Histologically, these lesions are unencapsu!ated tumors believed to arise from the nerve fascicles. 3 One third of these lesions occur in patients with neurofibromatosis type 1 (NF-1), whereas two thirds of CaSes are sporadic. Neurofibromas arising in patients with NF-1 occur with equal incidence in males and females. These tumors are characteristically multiple and plexiform in appearance with diffuse involvement of the brachial plexus. In contrast, sporadic neurofibromas are seen more commonly in females (2:1 to 3:1 female-to-male ratio). Sporadic neur0fibromas typically are solitary and probably originate in the supraclavicular brachial plexus. 3 Schwannomas are the second most common neural tumor involving the brachial plexus. Histologically, these lesions are encapsulated, thereby often permitting surgical excision without sacrificing the adjacent nerves. The majority of schwannomas are solitary, and they are slightly more common in the upper brachial plexus. 3 The imaging features of solitary neurofibromas are essentially indistinguishable from those of schwannomas. On CT, these lesions have attenuation similar to that of muscle, and they enhance variably with contrast (Fig 11). Both tumors may be associated with bony remodel-
MUKHERJI, CASTILLO, AND WAGLE
ing. On MRI, these two lesions are isointense to muscle on Tl-weighted sequences and hyperi ntense on T2-weighted sequences. Both tumors typically enhance after intravenous gadolinium administration (Fig 12). The diagnosis of neurofibroma may be made with a high degree of confidence if the lesions tiave a plexiform appearance or occur in a patient with NF-12,23 (Figs 13-15). Malignant neural tumors are very rare and consist mostly of fibrosarcomas 3,24,25and neurogenic sarcomas (malignant neurofibromas). These lesions occur most commonly in patients with neurofibromatosis type 1, especially after radiation therapy. 3,26 The imaging features of malignant neural tumors are similar to those of their benign counterparts, thus making it difficultto differentiate benign from malignant processes based on a single imaging study (Fig 16). The diagnosis of a malignant nerve sheath tumor may be suggested by a progressively enlarging mass in a patient with NF-1. Secondary neoplasms may extend to involve the adjacent brachial Plexus. These lesions may be either benign or malignant. Benign masses that involve the brachial plexus include lipoma, lipoblastoma, desmoid, lymphangioma, myoblastoma, osteochondroma, and ganglioneuroma 24,25 (Fig 17). Malignant neoplasms that may involve the
Fig 13. Plexiform neurofibroma. Axial gadolinium-enhanced Tl-weighted study performed in a patient with neurofibromatosis type I shows the characteristic appearance of plexiform neurofibromas.
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Fig 14. Piexiform neurofibroma. Axial T2-weighted image obtained in a patient with neurofibromatosis type I shows multiple high.signal masses situated between the anterior (A) and middle (M) scalene muscles. This location indicates that these neurofibromas are arising from the brachial plexus,
brachial plexus commonly result from direct extension from a Pancoast's tumor or because of metastatic disease. Involvement of the brachial plexus by direct extension of a Pancoast's tumor may be suspected in patients who present with supraclavicular pain, weakness, and paresthesias. Long-standing involvement may result in muscle wasting, z7 Imaging findings suggestive of brachial plexus invasion by a superior sulcus tumor are obliteration of the apical fat and proximity of the mass to the brachial plexus (Fig
18). Tumors that have been reported to metastasize to the brachial plexus include breast, lymphoma, bladder, gastrointestinal, testicular, thyroid, lung, melanoma, head and neck, and sarcomas 24,25(Figs 19 and 20). The imaging modality of choice in patients with possible neoplastic invasion of the brachial plexus is MRI because of its multiplanar capability and high soft tissue characterization. Previous studies have shown MRI to have a high sensitivity (100%) in detecting neoplastic in-
Fig 15. Plexiform neurofibroma. Noncontrast Tl-weighted study performed in a patient with neurofibromatosis type I shows multiple piexiform neurofibromas. The encasement of the subclavian artery (curved arrow) by these lesions indicates that the brachial plexus is involved by this process,
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MUKHERJI, CASTILLO, AND WAGLE
Fig 16 Neurofibrosarcoma. (A) Axial, gadolinium-enhanced, Tl-weighted image shows a neurofibrosarcoma (T) situated anterior to the middle scalene muscle (M) and adjacent to the subclavian artery (A). (B) Sagittal, gadolinium-enhanced, Tl-weighted image shows the tumor (T) adjacent to the subclavian artery (A) and in the expected position of the brachial plexus. (Compare with Fig 4.)
volvement of the brachial plexus. 28 The extent of disease also is depicted better with MRI than with CT. 29 Coronal Tl-weighted images are especially helpful for assessing the status of the apical fat in patients with Pancoast's tumors and for evaluating the relationship of masses to the brachial plexus.
Inflammatory Processes Inflammatory processes that may involve the brachial plexus include radiation therapy, neuri-
tis, and infections. Radiation therapy (RT) may injure the brachial plexus and cause a plexopathy. Three classic syndromes of RT-induced brachial plexopathy have been described. The most common form is a delayed progressive radiation fibrosis. 3°-32 The remaining two forms of radiation damage are a reversible or transient plexopathy 3°,33 and an acute ischemic plexopathy.30, 34 Radiation-induced brachial plexopathy is the most common and most severe peripheral ner-
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Fig 16. (cont'd.} (C) Axial, fatsaturated, Tl-weighted image shows abnormal enhancement along the supraclavicular position of the brachial plexus (curved arrow}, suggestive of perineural extension. A, anterior scalene muscle; M, middle scalene muscle. (D) Sagittal, fat-saturated, gadolinium-enhanced, T1weighted image obtained at the level of the neural foramina shows abnormal enhancement of the C7 and C8 nerve roots (straight arrows}, suggestive of perineural extension. Compare this with the normal appearance of the T1 nerve root (curved arrow). These findings were con. firmed at surgery.
vous system complication of RT. Radiation damage to the brachial plexus appears to be dose related and most likely occurs in patients who have received doses in excess of 6,000 cGy. 35 This damage is seen most commonly in women who have been treated with R T for breast cancer. The plexopathy tends to be delayed and progressive with the majority of
patients presenting at least 6 months after the completion of RT. The initial symptoms include paresthesias, followed by pain and weakness. These symptoms typically occur in an upper trunk distribution with weakness of the arm flexors and shoulder abduction. 36 Pain can accompany these paresthesias, but it usually occurs late in the course of this syndrome. 35
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Fig 17. Lipoma. (A) Coronal Tl-weighted image shows a lipoma arising from the left supraclavicular region. (B) Axial T1weighted image shows that the lipoma surrounds the cords of the brachial plexus (arrows),
However, other reports suggest that RT-induced plexopathies are generalized and that the distribution of the deficits is not helpful in differentiating this variety of plexopathy from a neoplastic one. 3 Histologically, in RT-induced plexopathy, there is dense fibrous tissue encasing the brachial plexus with wallerian degeneration. 37 On physical examination, radiationinduced brachial plexopathy may result in reflex abnormalities, intrinsic muscle weakness, muscle atrophy, and lymphedema.
MRI is the modality of choice for evaluating patients previously treated with RT to the supraclavicular region. 38,39The imaging findings of RT-induced brachial plexopathy are diffuse thickening and enhancement of the brachial plexus without a focal mass 2,3° (Fig 21). The presence of a focal mass in a patient treated with RT is suspicious for recurrent tumor and requires further evaluation, especially in patients treated with doses of less than 6,000 cGy. Horner's syndrome is caused rarely by RT alone
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Fig 18. Pancoast's tumor. (A) Coronal, noncontrast, Tl-weighted image shows a left superior sulcus tumor (T) that has extended into the subpleural fat and has invaded the lower trunk of the brachial plexus. The black arrowheads denote the C8 and T1 roots before formation of the lower trunk. (B) Sagittal, noncontrast, T1-weighted image shows that the mass has invaded the lung apex and encased the lower trunk of the brachial plexus, Not e the normal appearance of the upper and middle trunks of the brachial plexus (black arrowheads).
and, when present, also strongly suggests recurrent tumor. Active inflammation of the brachial plexus is termed brachial neuritis. Its etiology may be a primary viral infection (eg, cytomegalovirus, coxsackie) or a complication from prior infection. Brachial neuritis also may result as a complication of the previous administration of a serum vaccine, antibiotic, or other drug. Idiopathic and heredofamilial forms of brachial neuritis also have been described. 37 Patients with brachial neuritis typically present between
the third and seventh decades of life. The condition is slightly more common in males than in females (2.4:1). Clinically, these patients present with an ache in the supraclavicular region and shoulder. The pain often worsens over a 3- to 10-day period and may be followed by weakness and sensory and reflex impairment: In most cases, the disease is self-limited and subsides over a 6- to 12-week period. However, residual deficits occur in some patients. 37 MRI is the modality of choice in patients suspected of having brachial neuritis. The MRI findings are
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Fig 19, Breast metastases. Noncontrast, coronal, Tl-weightjed study performed in a patient previously treated for breast Carcinoma who presented with a left brachial plexopathy. The study shows a mass in the left supraclavicular region (large arrow). The fact that the mass surrounds the subclavian artery (small arrow) suggests that the mass involves the brachial plexus.
diffuse thickening, abnormal T2-weighted signal intensity, and abnormal enhancement of the brachial plexus on gad01inium-enhanced images 2 (Fig 22). Infectious processes involving the brachial plexus most commonly involve its supragangli0nic portion and typically are caused by discitis with associated epidural abscesses. Involvement of the more distal components of the brachial
Fig 20. Squamous cell carcinoma metastases. Noncontrast, coronal, Tl-weighted study performed in a patient with metastatic squamous cell carcinoma who presented with pain and weakness in the left arm, The study shows a large mass (curved arrow) encasing the subclavian artery (a), indicative of brachial plexus involvement. Note the normal appearance of the cords of the brachial plexus (straight arrows) and their relationship to the subclavian artery (a) on the uninvolved side.
plexus is unusual and may be caused by extension from an adjacent infection. Miscellaneous Causes
The clinical symptoms Of degenerative cervical disk disease may mimic those of a brachial plexopathy; therefore, evaluation of the cervical spine should be included in imaging studies of the brachial plexus. Eighty Percent to ninety
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Fig 21, Radiation-induced brachial plexopathy, (A) Coronal, noncontrast, T1-weighted image obtained in patient with breast carcinoma treated with radical mastectomy and 6,000 cGy of radiation who presented 1 year after RT with tingling in the fingers of the left hand, The study shows diffuse thickening of the brachial plexus (arrows) without evidence of a focal mass, (B) Sagittal, noncontrast, Tl-weighted image shows thickening of the cords of the brachial plexus (arrows). Biop* sies of this region showed fibrosis without evidence of tumor, a, subclavian artery. (Courtesy of Pamela Van Tassel, MD, Medical University of South Carolina, Charleston, SC,)
percent of cervical radiculopathies involve the C6 (C5/C6 disk) and C7 (C6/C7 disk) roots. Patients may Present with numbness, pain, sensory loss, and diminished reflexes at the affected levels. These symptoms may be exacerbated by
Fig 22. Idiopathic brachial neuritis. Axial T2-weighted image in a patient with biopsyproven hypertrophic interstitial neuritis of the brachial plexus shows fusiform enlargement and abnormal increased signal of the brachiai plexus (arrows), A, anterior scalene muscle; M, middle scalene muscle, (Courtesy of Kent Remley. MD~ University of Minnesota, Minneapolis, MN,)
coughing, sneezing, or lateral head movements. 23 Brachial plexopathy also may be caused by cervical ribs. Cervical ribs are present in approximately 1% of the population and are symptom-
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Fig 23. CT-guided neurolysis of the brachial plexus. This 70year-old man with metastatic squamous cell carcinoma involving the left brachial plexus and chest wall presented with left upper extremity paralysis and severe pain that was poorly controlled on high-dose analgesic therapy. (A) Axial CT image shows that the tip of a 20-gauge needle has been advanced between the plane of the anterior (a) and middle (m) scalene muscles and thus is in the expected location of the supraclavicular brachial plexus. (B) CT performed after administration of a mixture of Contrast material and alcohol. The study Shows that the mixture is extending along the expected location of the brachial plexus; After the procedure, the patient had a significant reduction in pain and was able to reduce his analgesic medication by 50%.
atic in 10% of affected individuals. 23,4°They are more common in females than in males (2:1) and are unilateral in 50% to 80% of individuals. Occasionally, a cervical rib may be attached to the first rib by a fibrous band. The brachial plexus may be affected by cervical ribs in one of two way s . The cervical rib may be positioned so that the brachial plexus must cross over it to enter the axilla, thereby stretching the lower trunk. Second, t h e cervical rib may narrow the space between the posterior aspect of the first
rib and the anterior scalene muscle, thus reducing the area through which the brachial plexus and subclavian artery course.Z3 ,4°,4l The cervical rib syndrome is believed to result from compression of the lower trunk of the brachial plexus as it crosses over the cervical rib or by compression of the lower trunk by a fibrous band that attaches to the first rib. This syndrome is more common in females. The symptoms consist of pain a n d / o r parasthesias along the ulnar border of the forearm and hand and motor weakness in
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a similar distribution. Continued compression may result in muscle wasting that initially involves the thenar eminence but may also spread to involve the small muscles of the hand. 23,42 BRACHIAL PLEXUS INTERVENTION
A variety of interventional procedures can be performed on the brachial plexus using CT guidance. 43,44Percutaneous biopsies of indeterminate masses adjacent to the brachial plexus may be performed safely in patients with previously treated malignancies, thereby avoiding the need for open surgery. 43 CT also may be used for needle localization for prognostic nerve
root blocks in patients with a mononeuropathy caused by for aminal stenosis. 44 Phenol neurolysis of the brachial plexus using CT-guided needle localization may be performed in patients with intractable plexopathy from advanced metastatic disease 42 (Fig 23). CT guidance provides more accurate needle localization, especially in patients with anatomy that has been distorted by tumor extension. By combining the ablative agent with contrast material, the extent of the neurolysis can be visualized with CT. These procedures are reserved for patients whose pain has been poorly controlled with high doses of analgesic medication. 4z
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