You are in: eMedicine Specialties > Radiology > BRAIN/SPINE Brachial Plexus, MRIArticle Last Updated: Apr 3, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 9
  Author: Sudhakar R Satti, MD, BS, Staff Physician, Department of Radiology, Hahnemann University Hospital Sudhakar R Satti is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, Radiological Society of North America, and Society of Radiologists in Ultrasound Coauthor(s): Christopher Cerniglia, DO, MEng, Magnetic Resonance Imaging Fellow, Instructor of Imaging Sciences, Department of Imaging Sciences, University of Rochester Medical Center; Ajit Belliappa, MD, Staff Physician, Department of Diagnostic Radiology, Hahnemann Hospital; Steven P Meyers, MD, Associate Professor, Department of Radiology, University of Rochester Medical Center; Robert A Koenigsberg, DO, MSc, FAOCR, Director of Neuroradiology, Professor, Department of Radiology, Drexel University College of Medicine Editors: Barton F Branstetter IV, MD, Assistant Professor of Radiology and Otolaryngology, University of Pittsburgh; Director of Head and Neck Imaging, Associate Director of Informatics, Department of Radiology, Division of Neuroradiology, University of Pittsburgh Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; C Douglas Phillips, MD, Professor, Departments of Radiology, Neurosurgery, and Otolaryngology, University of Virginia Health Sciences Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, EdM, MBA, Professor, Department of Radiology, Section Head of Musculoskeletal Radiology, Vice Chairman for Radiology Informatics, University of Washington Author and Editor Disclosure Synonyms and related keywords: thoracic outlet syndrome, upper-extremity weakness, upper-extremity paresthesia, upper extremity weakness, upper extremity paresthesia, arm weakness, arm paresthesia, birth trauma, Erb-Duchenne palsy, Dejerine-Klumpke palsy, traumatic meningocele, neurofibroma, thoracic outlet syndrome BACKGROUNDSection 2 of 9
  Evaluation of the brachial plexus is a clinical challenge. Physical examination has traditionally been a mainstay in evaluating and localizing pathology involving the brachial plexus. Physical examination is especially difficult in patients with scarring and fibrosis secondary to surgery or irradiation. Electrophysiologic studies can be used to detect abnormalities in nerve conduction, but they are poor for localizing a lesion. MRI has become increasingly important in the evaluation of brachial plexus pathology, as the technology and resolution has improved. Correlation of imaging results with electrophysiologic findings increases overall specificity and sensitivity. According to Nardin et al,1 electromyelography (EMG) and MRI examinations are complementary. Their study demonstrated that the sensitivity of EMG and MRI were 72% and 60%, respectively. Plain radiography can depict large lesions affecting the brachial plexus. However, radiographs are far less sensitive than other studies. CT has increased sensitivity for depicting extrinsic masses that compress the nerves; however, it offers poor soft tissue contrast to directly evaluate the nerves. With the advent of MRI, nerves that compose the brachial plexus can now be directly evaluated. Intrinsic and extrinsic pathology can be evaluated. Exact anatomic components of the brachial plexus, such as the roots, trunks, divisions, and cords, can be identified. MRI has the additional benefit of multiplanar imaging and increased soft tissue contrast. The tissue resolution of MRI is constantly improving with new pulse sequences and coil designs. With radiography and CT, changes in the shape or position of the brachial plexus were used to assess pathology. With MRI, the nerve can be directly visualized and evaluated for pathology. MRI sequences such as fat-saturated T2-weighted spin-echo, short-tau inversion recovery (STIR), and gadolinium-enhanced T1-weighted spin-echo sequences help in depicting subtle changes in the signal intensity of the nerves or enhancement and aid in refining the differential diagnosis. In addition, maximum intensity projections can make localization and visualization of the pathology most understandable for referring clinicians and surgeons. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with troublemoving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. NORMAL ANATOMYSection 3 of 9
The brachial plexus provides sensory and motor innervation to the upper extremity. The brachial plexus is a network of nerves originating form the ventral branches of spinal nerves C5-T1 in the posterior triangle of the neck. The nerves extend laterally along a slightly anteroinferior course, and they terminate in the axilla lateral to the pectoral minor as the musculocutaneous, axillary, radial, median, and ulnar nerves. To understand the brachial plexus we must first review the thoracic outlet. The first rib divides the cervicoaxillary canal into a proximal space and the axilla. Compression of the brachial plexus most often occurs proximally. The proximal space consists of the costoclavicular space and the scalene triangle. The costoclavicular space is bounded by the clavicle superiorly, the first rib inferiorly, the costoclavicular ligament anteromedially, and the scalenus medius muscle posterolaterally. The scalene triangle is bounded by the scalenus anticus (anterior scalene) anteriorly, the scalenus medius posteriorly, and the first rib inferiorly. The brachial plexus can also be entrapped in the pectoralis minor tunnel, which is bounded by the pectoralis minor tendon and the coracoid process. The most common cause of brachial plexus compression is an abnormal insertion of the anterior scalene on the first rib. The anterior scalene muscle originates from the anterior tubercles of the transverse processes of C3-6. This muscle runs inferior and deep to the sternocleidomastoid muscle and inserts onto the first rib. The anterior scalene separates the subclavian vein from the roots of the brachial plexus and the subclavian artery. Relative to the anterior scalene muscle, the subclavian vein is a superficial structure, and the brachial plexus and subclavian artery are deep structures. The anterior scalene divides the subclavian artery is divided into 3 segments. The first segment lies medial to the muscle, the second segment lies deep to the muscle, and the third segment extends from the lateral border of the muscle to the outer margin of the first rib. In summary, the anterior scalene muscle is an important anatomic landmark to localize the brachial plexus. The brachial plexus is divided into supraclavicular and infraclavicular parts. From proximal to distal, the brachial plexus is composed of 5 roots, 3 trunks, 6 divisions, 3 chords, and 5 terminal branches. Several nerves originate from the trunks and cords of the plexus to innervate the axilla and shoulder girdle (see Image 1). Roots The 5 roots are derived from the ventral rami of the spinal nerves C5-8 and T1, with minor contributions from C4 and T2. Before the roots combine into trunks, several small nerves arise from the plexus: The dorsal scapular nerve originates from the C5 root and the long thoracic nerve is derived from branches of the roots of C5-7. At the level of the interscalene triangle, the C5 and C6 roots combine to form the superior trunk, the C7 root becomes the middle trunk, and the C8 and T1 roots combine to form the inferior trunk. Trunks The 3 trunks pass between the anterior and middle scalene muscles and lie in the scalene triangle. They are named for their relationship with each other. The superior trunk is formed by the C5 and C6 roots. The suprascapular nerve (C5 and C6) and the subclavius nerve (C5 and C6) both originate from the superior trunk. Each trunk divides to form anterior and posterior division. Divisions The 6 divisions, 3 anterior and 3 posterior, lie approximately posterior to the clavicle. The 6 divisions form 3 cords at the level of the lateral margin of the first rib. The 3 posterior divisions form the posterior cord, the anterior divisions from the superior and middle trunk combine to form the lateral cord, and the anterior division of the inferior trunk becomes the medial chord. Cords The cords are positioned lateral to the first rib within the axilla and are named for their relationship to the axillary artery. A number of nerves arise from the 3 cords (see Image 1). As the cords exit the axilla, they recombine into terminal branches. Terminal branches The musculocutaneous nerve (C5-7) originates as a terminal branch of the lateral chord. The axillary nerve (C5-6) is a branch of the posterior cord, the other branch being the radial nerve (C5-8, T1). The ulnar nerve (C7-8, T1) is a terminal branch of the medial cord. The median nerve is formed as a terminal branch of both the medial and lateral cords. TECHNIQUE AND IMAGING PARAMETERSSection 4 of 9
Radiofrequency coil A surface coil provides resolution higher than that of a body coil, but it increases artifact due to respiratory motion. A combination of each may be used in sequences for the brachial plexus. As such, the surface coil is used for the spinal cord and exiting spinal nerve roots, whereas the body coil is used to image the plexus lateral to the interscalene triangle. Field of view Examination of the brachial plexus begins with the roots and trucks in the proximal aspects within the supraclavicular region and continues to the origin of the terminal branches at the lateral margin of the pectoralis minor muscle in the infraclavicular region. The field of view (FOV) is 17-22 cm for the direct coronal orientation and 14-17 cm for sagittal or oblique sagittal orientations. Matrix A matrix of 512 X 256 or 512 X 512 is used. Section thickness The recommended section thickness is 4 mm with an intersection gap of 0-0.5 mm for direct coronal imaging and 4 mm with an intersection gap of 1-2 mm for sagittal or oblique sagittal imaging. If axial images are obtained, 4-mm thickness with a 1- to 1.5-mm intersection gap may be performed. Orientation Images should be obtained in 2 planes. Direct coronal plane imaging is preferred over oblique coronal imaging because the brachial plexus has a shallow obliquity relative to the true coronal plane and because it can be imaged on 1 or 2 coronal sections. Cross-sectional imaging of the nerve components of the plexus may be performed by using either the true sagittal or the oblique sagittal plane on the side of interest. True sagittal imaging allows for comparison with the standard cross-sectional anatomy, which some find helpful in the recognition of appropriate anatomic landmarks. However, oblique sagittal imaging represents the true cross-section of the plexus more accurately than true sagittal imaging and thus allows for increased sensitivity to pathology, including changes in caliber, alteration in signal intensity, or presence of a fascicular pattern to the nerve components. Some institutions include a contrast-enhanced T1-weighted axial sequence as part of their routine evaluation of the brachial plexus. Pulse sequences T1- and T2-weighted images are obtained with identical parameters in terms of FOV, matrix, section thickness, and imaging plane. STIR or frequency-selective fat-saturation methods may be used for T2-weighted MRI to increase the conspicuity of abnormal signal intensity from the signal intensity of adjacent fat. Each has its advantages and disadvantages. STIR has been described as being more reliable than the other method because of its uniform and consistent fat suppression and excellent T2-like contrast when long repetition times are used. The STIR method has several disadvantages. For example, it has a relatively low signal-to-noise ratio, it offers relatively low tissue contrast, and it is more susceptible to flow artifacts than other methods. In contrast, frequency-selective fat-saturation methods have the advantage of an improved signal-to-noise ratio, T1-weighted imaging, and reduced flow-related artifacts. The major disadvantage of this type of fat suppression is the nonuniformity of fat suppression with the FOV primarily from inhomogeneity of B0. This variability in fat suppression is exacerbated by the nonuniformity in B1. When radiation injury, neoplasm, infection, or inflammatory etiologies are present or suspected, contrast-enhanced fat-suppressed T1-weighted MRI should be performed. The suggested protocol is summarized in Image 2. IMAGING APPROACH TO THE BRACHIAL PLEXUSSection 5 of 9
The roots of the brachial plexus enter the supraclavicular fossa as they pass through the interscalene triangle. At the lateral margin of the scalene triangle, the roots form 3 trunks, which travel posterior and superior to the subclavian artery. The brachial plexus can be easily identified on MRI by first identifying the anterior scalene muscle. The brachial plexus and subclavian artery (relationship outlined above) are deep to the anterior scalene. Normal components of the brachial plexus have low signal intensity on images obtained with all sequences and are surrounded by fat. The roots are best seen on axial images, whereas the remaining components are well seen on coronal and sagittal images.2 SYMPTOMSSection 6 of 9
Injury to the brachial plexus is associated with weakness and paresthesias of the upper extremity on the affected side. Thorough neurologic examination can be performed to localize the injury and to help the radiologist pinpoint the location of pathology. PATHOLOGIC CONDITIONSSection 7 of 9
Mechanisms of injury to the brachial plexus can be divided as traumatic, extrinsic compression, irradiation, entrapment, or invasion. Trauma Traumatic injuries to the brachial plexus occur along a spectrum ranging from disruption of the axonal fibers with preservation of the nerve sheath to complete transection of the nerve. MRI is useful in localizing the injury and, with electrophysiologic studies, in evaluating the severity of the injury. This information contributes to determining which injuries should be surgically repaired.3 Electrophysiologic studies are limited in determining if the nerve is completely avulsed along with its root or if the nerve is transected at the neural foramina, leaving its root with the spinal cord. Mechanisms that contribute to injury of the brachial plexus include shearing, compression, stretching, and transection. The most common injury involves avulsion of the nerve root at the level of the spinal cord secondary to a stretching of the nerve. The associated clinical scenario involves the patient's head moving away from his or her arm, which is in a fixed position. These injuries occur in childbirth (see Images 3-5) and in motor vehicle accidents (see Images 6-8). Erb-Duchenne palsy results from injury to the upper trunks at C5 and C6 and is the most common cause of brachial plexus injury in the field of obstetrics. Dejerine-Klumpke palsy results from injury to the C8 and T1 roots of the lower trunks. The mechanism is impaction of the shoulder with a stretch injury to the nerve at the root. These injuries often spontaneously resolve in several months. Pain with shoulder abduction, extension, and external rotation can be localized to injury of the C5 nerve root. Pain with elbow flexion, hand pronation and supination, and wrist extension suggest underlying C6 root involvement. If diffuse loss of function occurs without complete paralysis, it may be related to C7 nerve supply to the latissimus dorsi muscle. The C8 nerve root involves extensors, finger flexors, wrist flexors, and intrinsic hand muscles. T1 fibers control the intrinsic hand muscles.4 Traumatic injury to the brachial plexus is often associated with fractures, and plain radiography is the initial modality of choice to evaluate this injury. Clinical symptoms caused by a hematoma compressing the nerve root are the same as those due to avulsion of a nerve root from the spinal cord. Myelography and CT were used to assess this condition in the past. MRI is a noninvasive option to evaluate the nerve fibers and extrinsic compression due to a hematoma. On MRI, an avulsed nerve root lacks low signal intensity in the fat of the neural foramen; this is best seen on T1-weighted projections.5 Laceration of the dural sleeve of the nerve can cause the leakage of CSF in an extradural location, creating a traumatic pseudomeningocele (see Images 9-13). Traumatic pseudomeningoceles are cerebrospinal collections that follow the nerve root from the neural foramina. The sensitivity of CT myelography for nerve-root avulsion is the same as that of MRI.6 MRI is also sensitive for traumatic pseudomeningocele. Clavicular fractures can injure the brachial plexus by means of direct shearing or compression (see Images 14-15). Long-term posttraumatic sequel of clavicle fractures, including fibrosis and scar formation, can cause clinically significant brachiopathy as well. Chronic fibrosis and scarring classically have low signal on T1- and T2-weighted images, and may have mild enhancement. MRI is especially useful in determining the anatomic extent of the clavicle, the fibrous tissue, and the nerves for planning and performing surgery.3 Extrinsic compression and invasion Extrinsic compression on the brachial plexus is an important cause of pathology. The nerves can be compressed or displaced. Similar clinical symptoms can be due to postirradiation changes, such as fibrosis and extrinsic masses. Although MRI has high spatial resolution and multiplanar acquisition capabilities, tumor recurrence can be difficult to differentiate from posttreatment changes.7 Masses involving the neck, supraclavicular region, and axilla that affect the brachial plexus include mesenchymal tumors, lymphadenopathy, primary tumors of the brachial plexus, lung cancers, and metastatic disease. Tumors arising from the mesenchyme, including hemangioma, cystic hygroma, and lipoma (see Images 16-17), may cause direct mass effect and compression of adjacent nerve roots. Supraclavicular lymphadenopathy related to carcinoma, infectious processes, or lymphoma (see Images 18-20), can cause mass effect on the brachial plexus and result in vascular or neural compromise. By using multiplanar acquisitions, the entire brachial plexus can be evaluated from the root to the cords.7 Primary tumors of the brachial plexus include schwannoma, malignant tumors of the peripheral nerve sheath, and plexiform neurofibroma (see Images 21-22). Schwannomas and neurofibromas are isointense relative to muscle on T1-weighted images, and they have a peripheral area of increased signal intensity with lower central signal intensity on T2-weighted images.8 This appearance has been called target sign; however, it is not specific, and schwannomas can have similar characteristics.7 Infiltrative tumors include sarcomas and fibromatosis. Aggressive fibromatosis is the most common benign tumor, and it frequently involves surrounding structures, including the muscle, tendon, and neurovascular bundle. The imaging features of malignant neural tumors are similar to those of benign tumors. Imaging characteristics that suggest malignancy include a progressively enlarging mass in a patient with neurofibromatosis type 1 (NF-1), a lack of the target sign, bone destruction, poorly defined margins, and heterogeneous contrast enhancement.8 The most common primary neurogenic tumor is the neurofibroma. One third of all neurofibromas are associated with NF-1. About 3-13% of all nerve-sheath neurofibromas are malignant. Two thirds of neurofibromas arise spontaneously.9 Distinguishing benign tumors from malignant tumors is difficult. Malignant tumors often have irregular borders, they are large, and they have heterogeneous signal intensity on spin-echo sequences. However, both benign and malignant tumors are enhancing after the administration of contrast material.5 Metastatic disease involving the axilla and supraclavicular region is common and associated with breast, lung, and head and neck cancers. If the metastatic disease involves the neurovascular bundle, vascular compromise can occur. Masses are usually isointense on T1-weighted images and hyperintense on T2-weighted images. These signal intensity characteristics are similar to those of lymph nodes, and differentiating the 2 can be difficult. Irradiation MRI is an important tool for assessing the brachial plexus treated with radiation therapy. Postirradiation changes often lead to fibrosis, a common result of axillary radiation in the treatment of breast cancer (see Images 23-24). Recurrence of disease or fibrosis can cause the symptoms of an injury to the brachial plexus. MRI is an important tool for differentiating the two causes. Postirradiation neuritis commonly occurs 5-30 months after treatment, with a peak at 10-20 months.9 MRI findings associated with postirradiation changes include a thick, enhancing brachial plexus without a discrete mass. Tumor is also enhancing; therefore, the recognition of a soft-tissue mass aids in differentiating between postirradiation effects and recurrence. Radiation also affects the soft tissues, which have low signal intensity on T1- and T2-weighted images.5 Entrapment The exact position of compression and entrapment of the brachial plexus can be determined by means of detailed neurologic and physical examination, and it is confirmed with MRI. MRI is useful in distinguishing between a mass lesion and anatomic compression. Three main areas of the brachial plexus can be compressed along its course: the interscalene triangle, the first thoracic rib and the clavicle, and the retropectoral minor space. These 3 locations are all classified as thoracic outlet syndromes. Thoracic outlet syndromes can involve the nerves, vessels, or both. Thoracic outlet syndrome is clinically associated with plexopathy of the lower truck. C8-T1 compression results in wasting of the muscles and paresthesias of the hand. Thoracic outlet syndromes may be related to fracture of the clavicle or congenital bands associated with the first thoracic rib and a rudimentary cervical rib, or they may be acquired secondary to hypertrophy of the scalene muscles. MRI can depict other causes and sequelae of trauma, such as a hematoma or fracture, which compress the brachial plexus. Early imaging features include thickening and edema. Late findings may include muscular atrophy in the distribution of the brachial plexus and atrophy of the plexus itself.8 MULTIMEDIASection 8 of 9
REFERENCESSection 9 of 9
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