M u s c u l o s k e l e t a l I m a g i n g • R ev i ew Tharin et al. Traumatic and Nontraumatic Causes of Brachial Plexopathy
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Musculoskeletal Imaging Review
Brachial Plexopathy: A Review of Traumatic and Nontraumatic Causes Baxter D. Tharin1, 2 Jonathan A. Kini1 Gerald E. York1 John L. Ritter 1 Tharin Bd, Kini JA, York GE, Ritter JL
OBJECTIVE. This article reviews brachial plexus anatomy in the context of key landmarks, illustrates common findings of traumatic and nontraumatic causes of brachial plexopathies, describes symptoms associated with these maladies, and explains how proper diagnosis impacts clinical decisions. CONCLUSION. Knowledge of brachial plexus anatomy and of the imaging sequelae of traumatic and nontraumatic plexopathies enables the radiologist to more easily identify these afflictions, thereby facilitating a multidisciplinary treatment plan and improving patient outcome.
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Keywords: anatomy, brachial plexus, imaging findings, injury, neuropathies DOI:10.2214/AJR.12.9554 Received July 1, 2012; accepted after revision October 14, 2012. The opinions expressed on this document are solely those of the authors and do not represent an endorsement by or the views of the U.S. Army or Air Force, the Department of Defense, or the U.S. Government. 1 Department of Radiology, San Antonio Military Medical Center, 3851 Roger Brooke Dr, Fort Sam Houston, TX 78234. 2
Present address: Department of Diagnostic Imaging, Mike O’Callaghan Federal Medical Center, 4700 Las Vegas Blvd N, Nellis AFB, NV 89191. Address correspondence to B. D. Tharin ([email protected]).
This article is available for credit. WEB This is a web exclusive article. AJR 2014; 202:W67–W75 0361–803X/14/2021–W67 © American Roentgen Ray Society
rachial plexopathy is a neurologic affliction that causes pain or functional impairment (or both) of the ipsilateral upper extremity. It may result from medical conditions and from violent stretching, penetrating wounds, or direct trauma. Given the morbidity associated with brachial plexopathy, radiologists should be familiar with plexus anatomy, able to recognize traumatic and nontraumatic plexopathies, and capable of communicating findings to referring providers in a manner that will ensure appropriate management. Evaluating the brachial plexus may seem daunting given the complexity of the anatomy and the relative infrequency of dedicated studies, typically in the form of MRI [1–3]. However, familiarity with the plexus in the context of adjacent, easily identifiable structures and with the typical appearances of plexopathies will allow a more confident evaluation. Furthermore, this understanding will enable the interpreter to better evaluate the plexus on nondedicated studies such as CT of the cervical spine, which is routinely performed in the setting of nontraumatic upper extremity weakness and trauma. Anatomy For many clinicians, the brachial plexus may seem like a confusing cluster of nerve fibers. Simply remembering the components of the plexus and which adjacent anatomic structures delineate each part makes the task more manageable. Working from proximal to distal, the components of the plexus with the
best imaging plane for evaluation and key adjacent anatomy will be described. The helpful mnemonic of “Radiology technologists drink cold beverages” (i.e., roots, trunks, divisions, cords, branches) can be used to remember the components of the brachial plexus [3]. The brachial plexus is formed by C5 through T1 spinal nerves and contains both anterior (motor) and posterior (sensory) rootlet fibers [4]. The first portion of the plexus, called roots, is named for the level from which they arise (C5–C8, T1). The axial plane (Fig. 1) best shows the anterior and posterior rootlets and the named roots exiting the neural foramina [2]. Note that each root is subdivided into preganglionic and postganglionic portions, which are demarcated by the dorsal root ganglion because this distinction has bearing on management issues [1, 4], which we discuss later. The anterior rami of the postganglionic portion continue as the plexus. More distal components include the trunks, divisions, cords, and branches (Fig. 2). All of the sections are most easily seen on coronal images, with the sagittal and axial planes used for problem solving [2]. The trunks, of which there are three, are positioned between the anterior and middle scalene muscles. The six divisions are lateral to the scalene muscles and cephalad to the clavicle. The three cords are caudal to the clavicle and medial to the lateral border of the pectoralis minor muscle. Another point of reference for the cords in the sagittal plane is the subclavian artery, which can be used to identify the medial, lateral, and posterior compo-
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Tharin et al. nents (Fig. 3). The five branch nerves, arising from the cords lateral to the lateral border of the pectoralis minor muscle, are as follows: radial and axillary (posterior cord), ulnar (medial cord), musculocutaneous (lateral cord), and median (medial and lateral cords). There are also named nerves arising from the plexus before the branches are formed. The interpreter should be aware of these nerves and the muscles that they supply because a pattern of muscle atrophy from denervation can provide a clue about the region of affliction. The long thoracic nerve, arising from the C5–C7 roots immediately after they exit the neural foramina, innervates the serratus anterior muscle. More laterally, the C5 root gives rise to the dorsal scapular nerve, which innervates the levator scapulae and rhomboid major and minor muscles. The suprascapular nerve comes from the upper trunk, courses through the scapular notch to innervate the supraspinatus muscle, and then continues lateral around the scapular spine to supply the infraspinatus muscle. The medial and lateral pectoral nerves arise from the medial and lateral cords, respectively. These nerves form an anastomotic loop to innervate the pectoralis major and minor muscles [5]. The following nerves arise from the posterior cord: upper and lower subscapular nerves (teres major and subscapularis muscles), thoracodorsal nerve (latissimus dorsi muscle), and axillary nerve (teres minor and deltoid muscles). MRI Technique The brachial plexus is routinely evaluated with MRI given the superb soft-tissue contrast of this modality [6]. At our institution, brachial plexus MRI is performed with a 1.5T system (Magnetom Avanto or Espree, Siemens Healthcare) or a 3-T system (Verio, Siemens Healthcare). We use a body coil for radiofrequency transmission and a six-channel body matrix coil in conjunction with a four-channel neck matrix coil for signal reception. Standard sequences include the following: a three-plane localizer sequence; an axial T2-weighted sequence using 3D turbo spin-echo imaging with variable flip angle (referred to as “SPACE” on Siemens equipment); axial, coronal, and sagittal T1-weighted sequences; and a fat-suppressed fluid-sensitive sequence in the form of either a T2-weighted sequence with frequency-selective fat saturation or a STIR sequence. Some imagers prefer to substitute a proton density–weighted sequence for T1 weighting in the coronal plane for improved contrast resolution. Addi-
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tional three-plane fat-suppressed contrast-enhanced sequences are performed depending on patient history—for example, for assessment of a suspected inflammatory process or evaluation of a subtle nerve root injury in the absence of additional findings of avulsion. An IV gadolinium-based contrast material is used, with the volume of contrast material determined by patient weight. All of the aforementioned images are acquired using a 5-mm slice thickness. The imaging planes are set slightly off axis, as detailed later, in an effort to either capture a longer portion of the plexus in each single slice or image perpendicular to the traversing nerve for improved soft-tissue delineation. The MRI technologist determines the through-plane coverage and the orientation of the three axes (Fig. 4). Axial oblique images, angled 5–10° downward from superomedial to inferolateral, are acquired from the level of the C4 to the T2 vertebral bodies. The vertebral body is placed at the edge of the FOV, rather than being centered, which typically affords visualization of the plexus through the proximal branches on the more caudal slices (Fig. 1C). Imaging in a sagittal oblique plane, approximately 15° off the vertical axis, is then performed from the ipsilateral neural foramen through the level of the glenohumeral joint. The coronal oblique plane is oriented 5–7° anterior to the horizontal axis (from the transverse process through the middle of the humeral head), and images are acquired from the level of the sternum through the spinous processes. In many instances, cervical spine MRI is performed in conjunction with a brachial plexus examination (Fig. 1B). The addition of cervical spine MRI permits evaluation of the entire cervical spine for fractures and ligamentous injuries in the trauma patient and for evaluation of the upper cervical spine for degenerative disease or other pertinent abnormalities in the nontrauma setting. For difficult cases, obtaining images of the unaf-
fected contralateral brachial plexus for comparison may be helpful [6]. This protocol is summarized in Table 1. MRI Search Pattern A suggested basic search pattern for evaluation of a brachial plexus MRI study begins with an axial T2-weighted sequence. The spinal cord should be centered within the thecal sac and without contour abnormality. Nerve rootlets are evaluated for contiguity with the spinal cord. The cord, rootlets, and preganglionic and postganglionic roots normally have a homogeneously low T2 signal intensity. Any abnormal signal intensity or fluid collection within the extradural space, neural foramina, or perivertebral space may indicate blood products or pseudomeningocele and should be correlated with findings on a T1-weighted sequence. The postganglionic roots and proximal trunks are well seen on axial sequences as they traverse between the anterior and middle scalene muscles. These muscles and the fat surrounding the nerves should be evaluated for edema, hemorrhage, and masses. Next, coronal sequences are used for assessment of the trunks through the branches because this axis provides the longest in-plane view of the plexus. In the absence of pathology, there should be a homogenous signal of the nerves, surrounding fat, and muscles. The clavicle, ribs, and muscles innervated by the plexus should be evaluated in this plane. Sagittal sequences are useful for further assessment of the cords. Because these nerves closely approximate the subclavian artery, they are difficult to differentiate from the subclavian artery in other planes. Any variation of the fat surrounding the vessel or nerves may indicate an abnormality. Also, a vascular abnormality (e.g., subclavian artery aneurysm) or mass effect from a displaced clavicle fracture can be detected. Attention should then focus on identifying secondary signs of plexus
TABLE 1: MRI Protocol for Three-Plane Localizer to Image Brachial Plexus Plane
Orientation (° Off Axis)
Sequences
Axial
5–10°
T2-weighted SPACE, T2-weighted with fat saturation or STIR, T1-weighted contrast-enhanceda with fat suppression
Coronal
5–7°
T2-weighted with fat saturation or STIR, T1-weighted or proton density–weighted, contrast-enhanceda with fat suppression
Sagittal
15°
T2-weighted with fat saturation or STIR, T1-weighted contrast-enhanceda with fat suppression
Note—SPACE = 3D turbo spin-echo with variable flip angle on Siemens Healthcare equipment. aIV gadolinium use as needed based on history.
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Traumatic and Nontraumatic Causes of Brachial Plexopathy abnormalities and other causes for neuropathy including muscle edema and atrophy from denervation, intervertebral disk abnormalities, and vertebral body or rib fractures. Last, localizer sequences are reviewed for abnormalities that may be visible only on these images (e.g., abnormalities of the posterior fossa of the brain, lungs, mediastinum, proximal humerus). If contrast-enhanced sequences have been performed, this search pattern is then applied to assess for abnormal enhancement. A summary of this search pattern is listed in Table 2. The approach for evaluating the brachial plexus on CT is similar to that described here. However, because soft tissues are not as easily delineated on CT, the interpreter must rely more on secondary evidence of mass effect or trauma including muscle asymmetry, fat stranding, fracture, and hematoma. Nontraumatic Plexopathy Nontraumatic brachial plexopathy can be from a localized mass effect or a more widespread inflammatory process [1]. Masses include primary and secondary tumors and nonneoplastic processes such as aneurysms and cervical ribs. Primary tumors arising from the nerves are seen in younger patients. These neoplasms may be sporadic and benign (e.g., schwannoma [Fig. 5]) or may result from a condition (e.g., neurofibromatosis type 1) with a genetic predisposition for both benign and malignant lesions (e.g., neurofibroma and malignant peripheral nerve sheath tumor) [4, 7, 8]. Secondary neoplasms seen in an older adults can cause a plexopathy from either direct extension or metastasis—most common-
ly, lung (Fig. 6) and breast cancer, respectively [3]. A cervical rib is a unique cause of brachial plexopathy in that the cause of a patient’s symptoms can be detected on conventional radiography (Fig. 7). Inflammatory processes have varied causes but all produce similar MRI findings: thickening with increased signal intensity and enhancement of multiple plexus nerves [4]. Therefore, clinical context is key in distinguishing these entities. Radiation fibrosis (Fig. 8) may be the cause in the setting of breast or lung cancer therapy when doses exceed 6000 cGy [3, 4, 7]. Other causes include infection, drug allergy, and rarely heredofamilial plexopathies (e.g., Charcot-Marie-Tooth disease) [4]. Last, a diagnosis of exclusion is postviral inflammation (Parsonage-Turner syndrome), which typically has an abrupt onset and resolves after 4–12 weeks [4]. Traumatic Plexopathy There are two distinctive populations affected by traumatic brachial plexopathy. The first is neonates who have sustained a traction injury due to shoulder dystocia during vaginal delivery [1, 3, 4]. This trauma leads to a flaccid ipsilateral upper extremity. Fortunately, in most cases of obstetric trauma the nerves of the plexus have been stretched rather than avulsed and signs of injury resolve within weeks to months [3–5]. When avulsion does occur, it is most frequently of the C5 and C6 roots with a resulting Erb palsy— arm adducted and internally rotated, wrist flexed. The sequelae of Erb palsy, rather than de novo identification of the avulsions caus-
TABLE 2: Basic MRI Search Pattern to Use for Evaluation of the Brachial Plexus With Example Imaging Findings From Provided Cases Plane
Evaluate
Figures Showing Example Pathologic Findings
Axial
Spinal cord and rootlets
11
Axial
Preganglionic and postganglionic roots and trunks
5A
Axial
Extradural and perivertebral spaces
Axial
Soft tissues surrounding plexus
Coronal
Trunks through branches
Coronal
Surrounding fat and adjacent scalene muscles
Coronal
Muscles innervated by brachial plexus
Coronal
Clavicle and ribs
Sagittal
Subclavian artery and surrounding cords
Sagittal
Muscles innervated by brachial plexus
Sagittal
Cervical spine
14Aa
Localizer
Posterior fossa, lungs and mediastinum, humerus
None
aStudies with these findings shown on CT.
11, 14Ba 12 5B, 6, 8, 12B, 13 10a None 7B and 7C None 9B
ing Erb palsy, are more often encountered in imaging (Fig. 9). The primary finding is progressive glenohumeral deformity secondary to muscle imbalance, which can be seen as early as 2 years of age [5]. The second population affected by traumatic brachial plexopathy is young men in the second and third decades [1–3]. These patients sustain blunt force injury after a fall from a height or a motorcycle or motor vehicle crash and penetrating injury from a gunshot. Given the forces involved with these mechanisms, recognition of these injuries may be delayed because of concomitant injuries to the head or spine that draw attention away from the brachial plexus. These intubated or otherwise noncommunicative patients may not be able to indicate upper extremity pain and may not have physical examination findings that are helpful to the clinician. Therefore, it is essential for the radiologist to identify causes of brachial plexopathy that can be ameliorated in the early posttrauma period before irreversible nerve damage and muscle atrophy occur. Causes of brachial plexopathy to identify include mass effect from bone fragments, foreign bodies, or hematomas (Fig. 10), which can be seen on CT at the time of presentation (Tharin BD, unpublished data). MRI findings of root avulsion (Fig. 11) include pseudomeningocele, which is highly indicative (seen in 80% of avulsions) but is not pathognomonic; the absence of rootlets or roots; and spinal cord signal intensity abnormality [1, 3, 8]. For penetrating trauma and traction injury without root avulsion, the MRI findings are a hematoma or soft-tissue edema along the missile path (Fig. 12) or force vector in the region of the plexus [4]. Increased T2 signal and enhancement of intact nerves suggest damage or impairment despite contiguity [1, 3] (Fig. 13). CT myelography is an alternative imaging modality for evaluating root avulsion if MRI is unavailable, is contraindicated, or yields equivocal results. Intrathecal contrast material migrating into a meningocele or the epidural space through the torn dura of an avulsed root is the most striking abnormal finding (Fig. 14). A less conspicuous indicator of injury is root asymmetry. A spectrum of and grading system for these findings has been described [1], although the details are beyond the scope of this article. For management purposes, traumatic brachial plexopathy is categorized as preganglionic, postganglionic, or both [1]. In all instances, physical therapy plays a central role in a multi-
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Tharin et al. disciplinary approach. With therapy alone, improved symptoms and function are expected in children and those with a stretch-type injury, whereas outcome is poorer in patients with root avulsions [2, 4]. For preganglionic brachial plexopathies, surgical intervention is complex given that lesions are not amenable to direct repair. In cases of severe loss of function from multilevel root avulsions, nerve transfer can be undertaken whereby another nerve is sacrificed and its intact root is attached to the damaged nerve stump. Restoring biceps function (C6) followed by restoring shoulder mobility (C5) are the primary objectives [1, 2]. With postganglionic injuries, the clinical implications are twofold. Acutely, traumatic mass effect should be identified for potential early surgical intervention to prevent irreversible atrophy of denervated muscles. If there is no significant mass effect or the mass is an insidious process, then the next consideration is the contiguity of the nerve fascicles. For in-
tact fascicles, conservative management is pursued. If fascicles are damaged, then nerve grafting is considered [1, 3]. This procedure involves excising the damaged plexus segment and bridging the gap with a nerve autograft using the sural, phrenic, spinal accessory, or medial pectoral nerve [2, 4]. Conclusion This article has reviewed the key anatomy of the brachial plexus and the relevant imaging findings of brachial plexopathies in the nontraumatic and traumatic settings. The reader should now possess a practical approach for the radiologic evaluation of the brachial plexus that will improve the diagnosis of brachial plexopathies and facilitate a multidisciplinary approach to treatment, thereby reducing the morbidity of these conditions. References 1. Yoshikawa T, Hayashi N, Yamamoto S, et al. Brachial plexus injury: clinical manifestations, con-
ventional imaging, findings, and the latest imaging techniques. RadioGraphics 2006; 26(suppl 1):S133–S143 2. Foster M. Traumatic brachial plexus injuries. eMedicine.com. http://emedicine.medscape.com/ article/1268993-overview. Accessed March 2011 3. Lury K, Castillo M. Imaging of the brachial plexus. Appl Radiol 2004; 4:28–32 4. Castillo M. Imaging the anatomy of the brachial plexus: review and self-assessment module. AJR 2005; 185(suppl 6):S196–S204 5. Canale ST, Campbell WC, eds. Campbell’s operative orthopaedics, 10th ed. Philadelphia, PA: Mosby, 2003:1349–1351, 3247–3255 6. Berquist TH, ed. MRI of the musculoskeletal system, 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006:558, 568–569, 646–650 7. Wittenberg K, Adkins M. MR imaging of nontraumatic brachial plexopathies: frequency and spectrum of findings. RadioGraphics 2000; 20:1023–1032 8. Posniak HV, Olson MC, Dudiak CM, Wisniewski R, O’Malley C. MR imaging of the brachial plexus. AJR 1993; 161:373–379
B A Fig. 1—Anatomy of brachial plexus: roots. A, Illustration shows first portion of brachial plexus, which is called roots; roots are subdivided into preganglionic (green) and postganglionic (orange) portions. Fibers from both anterior (motor) and posterior (sensory) rootlets (solid black arrows) contribute to anterior rami (open arrow), which continues as plexus. (Drawing by Toye CM) B, Axial T2-weighted MR image obtained using 3D turbo spin-echo imaging with variable flip angle (referred to as “SPACE” on Siemens equipment) at C5 level shows how axial plane is best plane for evaluating brachial plexus roots. Anterior and posterior rootlets (solid arrows) combine to form root (open arrow) that exits neural foramen. Note that vertebral body is centered in FOV, rather than at edge as described in standard protocol, because this example is from cervical spine MRI performed in conjunction with brachial plexus MRI. C, Axial T1-weighted MR image obtained near most caudal portion of FOV shows how this imaging plane can also be useful for cross-referencing brachial plexopathy abnormalities distal to roots and trunks. Traversing branches (solid arrows) are seen lateral to lateral border of pectoralis minor muscle (open arrow).
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Traumatic and Nontraumatic Causes of Brachial Plexopathy
A
B
C
Fig. 2—Anatomy of brachial plexus: trunks through branches. A, Illustration shows trunks (blue) positioned between anterior and middle scalene muscles, divisions (turquoise) lateral to scalene muscles and above clavicle, cords (pink) inferior to clavicle, and branches (magenta) lateral to expected location of lateral margin of pectoralis minor muscle. (Drawing by Toye CM) B and C, Coronal proton density–weighted (B) and coronal T1-weighted (C) MR images show that coronal plane is best for seeing more distal components of brachial plexus. In these images, trucks (solid white arrow, B), divisions (open arrow, B), cords (solid black arrow, B), and branches (arrows, C) are identified. Subclavian and axillary arteries (asterisks) are shown.
A
B
Fig. 3—Sagittal plane is helpful for further evaluation and problem solving. A, Sagittal T1-weighted MR image shows three individual cords—medial (open arrow), lateral (solid white arrow), and posterior (black arrow)—that are adjacent to subclavian artery (asterisk). B, More lateral MR image from same series as A shows branches (arrows).
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Tharin et al.
A
B Fig. 4—Orientation of imaging planes. A–C, Localizer MR images show how oblique alignment (lines) is set for axial (A), coronal (B), and sagittal (C) images of brachial plexus.
C
A Fig. 5—18-year-old woman with weak shoulder abduction, extension, and external rotation. A, Axial gradient-echo MR image shows schwannoma is affecting C5 postganglionic root (solid white arrow) and continues into more distal trunk (open arrow). B, Coronal STIR MR image shows trunk involvement (arrow) to better advantage than A.
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Fig. 6—62-year-old man with lung adenocarcinoma who presented with weakness in hand muscles. On this coronal T1-weighted contrast-enhanced MR image, mass (open arrow) is seen invading through pleura and affecting T1 nerve postganglionic root (solid white arrow), resulting in weakness in intrinsic muscles of hand.
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Traumatic and Nontraumatic Causes of Brachial Plexopathy
A
B
C
Fig. 7—33-year-old woman with left arm weakness. A, Radiograph shows bilateral (left larger than right) cervical ribs (arrows). B, Preoperative coronal T1-weighted MR image shows left cervical rib (thin arrow) is causing mass effect on distal trunks and proximal cords (thick arrow). C, Postoperative coronal T1-weighted MR image shows that cords (arrow) are no longer impinged by rib. Left arm weakness resolved. Fig. 8—Coronal fat-suppressed T2-weighted MR image of patient with cancer shows thickening and increased signal intensity (arrows) of left brachial plexus within radiation field. (Reprinted with permission of Anderson Publishing, Ltd., from Lury K., Castillo M. Imaging of the brachial plexus. Appl Radiol 2004; 4:28-32)
A
B
Fig. 9—Obstetric brachial plexopathy with resulting Erb palsy in 9-year-old girl. (Courtesy of Carlson CL, San Antonio Medical Center, Fort Sam Houston, TX) A, Three-dimensional reformation of thoracic CT, posterior view, shows ipsilateral scapula elevation (thick arrow) and anterior rotation as well as hypoplastic and dysplastic glenoid and humeral head (thin arrow). B, Sagittal T1-weighted MR image shows moderate atrophy of supraspinatus, infraspinatus, and subscapularis (arrows) muscles.
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Tharin et al.
Fig. 10—38-year-old man who sustained injuries from motorcycle crash. Coronal CT angiogram of neck obtained at time of injury shows left-sided hematoma (thin arrow) lateral to scalene muscles and in vicinity of subclavian artery. This finding should raise concern about mass effect of brachial plexus divisions and cords. Unaffected right side (thick arrow) is included for comparison.
A
Fig. 11—30-year-old man who presented with right upper extremity weakness 4 months after motor vehicle crash. Axial T2-weighted MR image shows avulsed root (thin arrow) within traumatic pseudomeningocele (thick arrow).
B
Fig. 12—25-year-old woman who sustained gunshot wound to upper thorax. A, Axial T2-weighted MR image obtained with fat suppression shows increased signal intensity (open arrows) along course of projectile and hematoma (solid white arrow) adjacent to cords (black arrow). B, Coronal STIR MR image shows edema and hematoma (thick arrow) surrounding cords and proximal branches (thin arrow). Surgical exploration to decompress hematoma before mass effect causes deafferentation should be considered in cases like this one.
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Fig. 13—38-year-old man with left brachial plexopathy after motor vehicle collision. Coronal STIR MR image shows increased signal intensity in left C6 root and superior trunk (arrow) consistent with stretch injury. Preganglionic root (not shown) was intact.
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Traumatic and Nontraumatic Causes of Brachial Plexopathy
A
B
Fig. 14—26-year-old man who sustained gunshot wound. Patient presented 3 weeks after injury with right upper extremity pain and weakness; at that time, CT myelography was performed because patient was unable to undergo evaluation with MRI given proximity of bullet to spinal cord. A, Sagittal CT myelogram shows that instilled intrathecal (solid black arrow) contrast material is in epidural space (open arrow) in cervical spine. This finding indicates dural disruption and raises suspicion for root avulsion. Beam-hardening artifact (white arrow) from adjacent bullet is noted. B, Axial CT myelogram provides further evidence of right root avulsion including spinal cord compression and displacement (straight solid arrow) to contralateral side, given absence of traction from injured nerve root; compression from epidural fluid and hemorrhage (open arrow); and pseudomeningocele (curved arrow). Arrowhead = surgical drain.
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Musculoskeletal Imaging Review
Brachial Plexopathy: A Review of Traumatic and Nontraumatic Causes Baxter D. Tharin1, 2 Jonathan A. Kini1 Gerald E. York1 John L. Ritter 1 Tharin Bd, Kini JA, York GE, Ritter JL
OBJECTIVE. This article reviews brachial plexus anatomy in the context of key landmarks, illustrates common findings of traumatic and nontraumatic causes of brachial plexopathies, describes symptoms associated with these maladies, and explains how proper diagnosis impacts clinical decisions. CONCLUSION. Knowledge of brachial plexus anatomy and of the imaging sequelae of traumatic and nontraumatic plexopathies enables the radiologist to more easily identify these afflictions, thereby facilitating a multidisciplinary treatment plan and improving patient outcome.
B
Keywords: anatomy, brachial plexus, imaging findings, injury, neuropathies DOI:10.2214/AJR.12.9554 Received July 1, 2012; accepted after revision October 14, 2012. The opinions expressed on this document are solely those of the authors and do not represent an endorsement by or the views of the U.S. Army or Air Force, the Department of Defense, or the U.S. Government. 1 Department of Radiology, San Antonio Military Medical Center, 3851 Roger Brooke Dr, Fort Sam Houston, TX 78234. 2
Present address: Department of Diagnostic Imaging, Mike O’Callaghan Federal Medical Center, 4700 Las Vegas Blvd N, Nellis AFB, NV 89191. Address correspondence to B. D. Tharin ([email protected]).
This article is available for credit. WEB This is a web exclusive article. AJR 2014; 202:W67–W75 0361–803X/14/2021–W67 © American Roentgen Ray Society
rachial plexopathy is a neurologic affliction that causes pain or functional impairment (or both) of the ipsilateral upper extremity. It may result from medical conditions and from violent stretching, penetrating wounds, or direct trauma. Given the morbidity associated with brachial plexopathy, radiologists should be familiar with plexus anatomy, able to recognize traumatic and nontraumatic plexopathies, and capable of communicating findings to referring providers in a manner that will ensure appropriate management. Evaluating the brachial plexus may seem daunting given the complexity of the anatomy and the relative infrequency of dedicated studies, typically in the form of MRI [1–3]. However, familiarity with the plexus in the context of adjacent, easily identifiable structures and with the typical appearances of plexopathies will allow a more confident evaluation. Furthermore, this understanding will enable the interpreter to better evaluate the plexus on nondedicated studies such as CT of the cervical spine, which is routinely performed in the setting of nontraumatic upper extremity weakness and trauma. Anatomy For many clinicians, the brachial plexus may seem like a confusing cluster of nerve fibers. Simply remembering the components of the plexus and which adjacent anatomic structures delineate each part makes the task more manageable. Working from proximal to distal, the components of the plexus with the
best imaging plane for evaluation and key adjacent anatomy will be described. The helpful mnemonic of “Radiology technologists drink cold beverages” (i.e., roots, trunks, divisions, cords, branches) can be used to remember the components of the brachial plexus [3]. The brachial plexus is formed by C5 through T1 spinal nerves and contains both anterior (motor) and posterior (sensory) rootlet fibers [4]. The first portion of the plexus, called roots, is named for the level from which they arise (C5–C8, T1). The axial plane (Fig. 1) best shows the anterior and posterior rootlets and the named roots exiting the neural foramina [2]. Note that each root is subdivided into preganglionic and postganglionic portions, which are demarcated by the dorsal root ganglion because this distinction has bearing on management issues [1, 4], which we discuss later. The anterior rami of the postganglionic portion continue as the plexus. More distal components include the trunks, divisions, cords, and branches (Fig. 2). All of the sections are most easily seen on coronal images, with the sagittal and axial planes used for problem solving [2]. The trunks, of which there are three, are positioned between the anterior and middle scalene muscles. The six divisions are lateral to the scalene muscles and cephalad to the clavicle. The three cords are caudal to the clavicle and medial to the lateral border of the pectoralis minor muscle. Another point of reference for the cords in the sagittal plane is the subclavian artery, which can be used to identify the medial, lateral, and posterior compo-
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Tharin et al. nents (Fig. 3). The five branch nerves, arising from the cords lateral to the lateral border of the pectoralis minor muscle, are as follows: radial and axillary (posterior cord), ulnar (medial cord), musculocutaneous (lateral cord), and median (medial and lateral cords). There are also named nerves arising from the plexus before the branches are formed. The interpreter should be aware of these nerves and the muscles that they supply because a pattern of muscle atrophy from denervation can provide a clue about the region of affliction. The long thoracic nerve, arising from the C5–C7 roots immediately after they exit the neural foramina, innervates the serratus anterior muscle. More laterally, the C5 root gives rise to the dorsal scapular nerve, which innervates the levator scapulae and rhomboid major and minor muscles. The suprascapular nerve comes from the upper trunk, courses through the scapular notch to innervate the supraspinatus muscle, and then continues lateral around the scapular spine to supply the infraspinatus muscle. The medial and lateral pectoral nerves arise from the medial and lateral cords, respectively. These nerves form an anastomotic loop to innervate the pectoralis major and minor muscles [5]. The following nerves arise from the posterior cord: upper and lower subscapular nerves (teres major and subscapularis muscles), thoracodorsal nerve (latissimus dorsi muscle), and axillary nerve (teres minor and deltoid muscles). MRI Technique The brachial plexus is routinely evaluated with MRI given the superb soft-tissue contrast of this modality [6]. At our institution, brachial plexus MRI is performed with a 1.5T system (Magnetom Avanto or Espree, Siemens Healthcare) or a 3-T system (Verio, Siemens Healthcare). We use a body coil for radiofrequency transmission and a six-channel body matrix coil in conjunction with a four-channel neck matrix coil for signal reception. Standard sequences include the following: a three-plane localizer sequence; an axial T2-weighted sequence using 3D turbo spin-echo imaging with variable flip angle (referred to as “SPACE” on Siemens equipment); axial, coronal, and sagittal T1-weighted sequences; and a fat-suppressed fluid-sensitive sequence in the form of either a T2-weighted sequence with frequency-selective fat saturation or a STIR sequence. Some imagers prefer to substitute a proton density–weighted sequence for T1 weighting in the coronal plane for improved contrast resolution. Addi-
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tional three-plane fat-suppressed contrast-enhanced sequences are performed depending on patient history—for example, for assessment of a suspected inflammatory process or evaluation of a subtle nerve root injury in the absence of additional findings of avulsion. An IV gadolinium-based contrast material is used, with the volume of contrast material determined by patient weight. All of the aforementioned images are acquired using a 5-mm slice thickness. The imaging planes are set slightly off axis, as detailed later, in an effort to either capture a longer portion of the plexus in each single slice or image perpendicular to the traversing nerve for improved soft-tissue delineation. The MRI technologist determines the through-plane coverage and the orientation of the three axes (Fig. 4). Axial oblique images, angled 5–10° downward from superomedial to inferolateral, are acquired from the level of the C4 to the T2 vertebral bodies. The vertebral body is placed at the edge of the FOV, rather than being centered, which typically affords visualization of the plexus through the proximal branches on the more caudal slices (Fig. 1C). Imaging in a sagittal oblique plane, approximately 15° off the vertical axis, is then performed from the ipsilateral neural foramen through the level of the glenohumeral joint. The coronal oblique plane is oriented 5–7° anterior to the horizontal axis (from the transverse process through the middle of the humeral head), and images are acquired from the level of the sternum through the spinous processes. In many instances, cervical spine MRI is performed in conjunction with a brachial plexus examination (Fig. 1B). The addition of cervical spine MRI permits evaluation of the entire cervical spine for fractures and ligamentous injuries in the trauma patient and for evaluation of the upper cervical spine for degenerative disease or other pertinent abnormalities in the nontrauma setting. For difficult cases, obtaining images of the unaf-
fected contralateral brachial plexus for comparison may be helpful [6]. This protocol is summarized in Table 1. MRI Search Pattern A suggested basic search pattern for evaluation of a brachial plexus MRI study begins with an axial T2-weighted sequence. The spinal cord should be centered within the thecal sac and without contour abnormality. Nerve rootlets are evaluated for contiguity with the spinal cord. The cord, rootlets, and preganglionic and postganglionic roots normally have a homogeneously low T2 signal intensity. Any abnormal signal intensity or fluid collection within the extradural space, neural foramina, or perivertebral space may indicate blood products or pseudomeningocele and should be correlated with findings on a T1-weighted sequence. The postganglionic roots and proximal trunks are well seen on axial sequences as they traverse between the anterior and middle scalene muscles. These muscles and the fat surrounding the nerves should be evaluated for edema, hemorrhage, and masses. Next, coronal sequences are used for assessment of the trunks through the branches because this axis provides the longest in-plane view of the plexus. In the absence of pathology, there should be a homogenous signal of the nerves, surrounding fat, and muscles. The clavicle, ribs, and muscles innervated by the plexus should be evaluated in this plane. Sagittal sequences are useful for further assessment of the cords. Because these nerves closely approximate the subclavian artery, they are difficult to differentiate from the subclavian artery in other planes. Any variation of the fat surrounding the vessel or nerves may indicate an abnormality. Also, a vascular abnormality (e.g., subclavian artery aneurysm) or mass effect from a displaced clavicle fracture can be detected. Attention should then focus on identifying secondary signs of plexus
TABLE 1: MRI Protocol for Three-Plane Localizer to Image Brachial Plexus Plane
Orientation (° Off Axis)
Sequences
Axial
5–10°
T2-weighted SPACE, T2-weighted with fat saturation or STIR, T1-weighted contrast-enhanceda with fat suppression
Coronal
5–7°
T2-weighted with fat saturation or STIR, T1-weighted or proton density–weighted, contrast-enhanceda with fat suppression
Sagittal
15°
T2-weighted with fat saturation or STIR, T1-weighted contrast-enhanceda with fat suppression
Note—SPACE = 3D turbo spin-echo with variable flip angle on Siemens Healthcare equipment. aIV gadolinium use as needed based on history.
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Traumatic and Nontraumatic Causes of Brachial Plexopathy abnormalities and other causes for neuropathy including muscle edema and atrophy from denervation, intervertebral disk abnormalities, and vertebral body or rib fractures. Last, localizer sequences are reviewed for abnormalities that may be visible only on these images (e.g., abnormalities of the posterior fossa of the brain, lungs, mediastinum, proximal humerus). If contrast-enhanced sequences have been performed, this search pattern is then applied to assess for abnormal enhancement. A summary of this search pattern is listed in Table 2. The approach for evaluating the brachial plexus on CT is similar to that described here. However, because soft tissues are not as easily delineated on CT, the interpreter must rely more on secondary evidence of mass effect or trauma including muscle asymmetry, fat stranding, fracture, and hematoma. Nontraumatic Plexopathy Nontraumatic brachial plexopathy can be from a localized mass effect or a more widespread inflammatory process [1]. Masses include primary and secondary tumors and nonneoplastic processes such as aneurysms and cervical ribs. Primary tumors arising from the nerves are seen in younger patients. These neoplasms may be sporadic and benign (e.g., schwannoma [Fig. 5]) or may result from a condition (e.g., neurofibromatosis type 1) with a genetic predisposition for both benign and malignant lesions (e.g., neurofibroma and malignant peripheral nerve sheath tumor) [4, 7, 8]. Secondary neoplasms seen in an older adults can cause a plexopathy from either direct extension or metastasis—most common-
ly, lung (Fig. 6) and breast cancer, respectively [3]. A cervical rib is a unique cause of brachial plexopathy in that the cause of a patient’s symptoms can be detected on conventional radiography (Fig. 7). Inflammatory processes have varied causes but all produce similar MRI findings: thickening with increased signal intensity and enhancement of multiple plexus nerves [4]. Therefore, clinical context is key in distinguishing these entities. Radiation fibrosis (Fig. 8) may be the cause in the setting of breast or lung cancer therapy when doses exceed 6000 cGy [3, 4, 7]. Other causes include infection, drug allergy, and rarely heredofamilial plexopathies (e.g., Charcot-Marie-Tooth disease) [4]. Last, a diagnosis of exclusion is postviral inflammation (Parsonage-Turner syndrome), which typically has an abrupt onset and resolves after 4–12 weeks [4]. Traumatic Plexopathy There are two distinctive populations affected by traumatic brachial plexopathy. The first is neonates who have sustained a traction injury due to shoulder dystocia during vaginal delivery [1, 3, 4]. This trauma leads to a flaccid ipsilateral upper extremity. Fortunately, in most cases of obstetric trauma the nerves of the plexus have been stretched rather than avulsed and signs of injury resolve within weeks to months [3–5]. When avulsion does occur, it is most frequently of the C5 and C6 roots with a resulting Erb palsy— arm adducted and internally rotated, wrist flexed. The sequelae of Erb palsy, rather than de novo identification of the avulsions caus-
TABLE 2: Basic MRI Search Pattern to Use for Evaluation of the Brachial Plexus With Example Imaging Findings From Provided Cases Plane
Evaluate
Figures Showing Example Pathologic Findings
Axial
Spinal cord and rootlets
11
Axial
Preganglionic and postganglionic roots and trunks
5A
Axial
Extradural and perivertebral spaces
Axial
Soft tissues surrounding plexus
Coronal
Trunks through branches
Coronal
Surrounding fat and adjacent scalene muscles
Coronal
Muscles innervated by brachial plexus
Coronal
Clavicle and ribs
Sagittal
Subclavian artery and surrounding cords
Sagittal
Muscles innervated by brachial plexus
Sagittal
Cervical spine
14Aa
Localizer
Posterior fossa, lungs and mediastinum, humerus
None
aStudies with these findings shown on CT.
11, 14Ba 12 5B, 6, 8, 12B, 13 10a None 7B and 7C None 9B
ing Erb palsy, are more often encountered in imaging (Fig. 9). The primary finding is progressive glenohumeral deformity secondary to muscle imbalance, which can be seen as early as 2 years of age [5]. The second population affected by traumatic brachial plexopathy is young men in the second and third decades [1–3]. These patients sustain blunt force injury after a fall from a height or a motorcycle or motor vehicle crash and penetrating injury from a gunshot. Given the forces involved with these mechanisms, recognition of these injuries may be delayed because of concomitant injuries to the head or spine that draw attention away from the brachial plexus. These intubated or otherwise noncommunicative patients may not be able to indicate upper extremity pain and may not have physical examination findings that are helpful to the clinician. Therefore, it is essential for the radiologist to identify causes of brachial plexopathy that can be ameliorated in the early posttrauma period before irreversible nerve damage and muscle atrophy occur. Causes of brachial plexopathy to identify include mass effect from bone fragments, foreign bodies, or hematomas (Fig. 10), which can be seen on CT at the time of presentation (Tharin BD, unpublished data). MRI findings of root avulsion (Fig. 11) include pseudomeningocele, which is highly indicative (seen in 80% of avulsions) but is not pathognomonic; the absence of rootlets or roots; and spinal cord signal intensity abnormality [1, 3, 8]. For penetrating trauma and traction injury without root avulsion, the MRI findings are a hematoma or soft-tissue edema along the missile path (Fig. 12) or force vector in the region of the plexus [4]. Increased T2 signal and enhancement of intact nerves suggest damage or impairment despite contiguity [1, 3] (Fig. 13). CT myelography is an alternative imaging modality for evaluating root avulsion if MRI is unavailable, is contraindicated, or yields equivocal results. Intrathecal contrast material migrating into a meningocele or the epidural space through the torn dura of an avulsed root is the most striking abnormal finding (Fig. 14). A less conspicuous indicator of injury is root asymmetry. A spectrum of and grading system for these findings has been described [1], although the details are beyond the scope of this article. For management purposes, traumatic brachial plexopathy is categorized as preganglionic, postganglionic, or both [1]. In all instances, physical therapy plays a central role in a multi-
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Tharin et al. disciplinary approach. With therapy alone, improved symptoms and function are expected in children and those with a stretch-type injury, whereas outcome is poorer in patients with root avulsions [2, 4]. For preganglionic brachial plexopathies, surgical intervention is complex given that lesions are not amenable to direct repair. In cases of severe loss of function from multilevel root avulsions, nerve transfer can be undertaken whereby another nerve is sacrificed and its intact root is attached to the damaged nerve stump. Restoring biceps function (C6) followed by restoring shoulder mobility (C5) are the primary objectives [1, 2]. With postganglionic injuries, the clinical implications are twofold. Acutely, traumatic mass effect should be identified for potential early surgical intervention to prevent irreversible atrophy of denervated muscles. If there is no significant mass effect or the mass is an insidious process, then the next consideration is the contiguity of the nerve fascicles. For in-
tact fascicles, conservative management is pursued. If fascicles are damaged, then nerve grafting is considered [1, 3]. This procedure involves excising the damaged plexus segment and bridging the gap with a nerve autograft using the sural, phrenic, spinal accessory, or medial pectoral nerve [2, 4]. Conclusion This article has reviewed the key anatomy of the brachial plexus and the relevant imaging findings of brachial plexopathies in the nontraumatic and traumatic settings. The reader should now possess a practical approach for the radiologic evaluation of the brachial plexus that will improve the diagnosis of brachial plexopathies and facilitate a multidisciplinary approach to treatment, thereby reducing the morbidity of these conditions. References 1. Yoshikawa T, Hayashi N, Yamamoto S, et al. Brachial plexus injury: clinical manifestations, con-
ventional imaging, findings, and the latest imaging techniques. RadioGraphics 2006; 26(suppl 1):S133–S143 2. Foster M. Traumatic brachial plexus injuries. eMedicine.com. http://emedicine.medscape.com/ article/1268993-overview. Accessed March 2011 3. Lury K, Castillo M. Imaging of the brachial plexus. Appl Radiol 2004; 4:28–32 4. Castillo M. Imaging the anatomy of the brachial plexus: review and self-assessment module. AJR 2005; 185(suppl 6):S196–S204 5. Canale ST, Campbell WC, eds. Campbell’s operative orthopaedics, 10th ed. Philadelphia, PA: Mosby, 2003:1349–1351, 3247–3255 6. Berquist TH, ed. MRI of the musculoskeletal system, 5th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006:558, 568–569, 646–650 7. Wittenberg K, Adkins M. MR imaging of nontraumatic brachial plexopathies: frequency and spectrum of findings. RadioGraphics 2000; 20:1023–1032 8. Posniak HV, Olson MC, Dudiak CM, Wisniewski R, O’Malley C. MR imaging of the brachial plexus. AJR 1993; 161:373–379
B A Fig. 1—Anatomy of brachial plexus: roots. A, Illustration shows first portion of brachial plexus, which is called roots; roots are subdivided into preganglionic (green) and postganglionic (orange) portions. Fibers from both anterior (motor) and posterior (sensory) rootlets (solid black arrows) contribute to anterior rami (open arrow), which continues as plexus. (Drawing by Toye CM) B, Axial T2-weighted MR image obtained using 3D turbo spin-echo imaging with variable flip angle (referred to as “SPACE” on Siemens equipment) at C5 level shows how axial plane is best plane for evaluating brachial plexus roots. Anterior and posterior rootlets (solid arrows) combine to form root (open arrow) that exits neural foramen. Note that vertebral body is centered in FOV, rather than at edge as described in standard protocol, because this example is from cervical spine MRI performed in conjunction with brachial plexus MRI. C, Axial T1-weighted MR image obtained near most caudal portion of FOV shows how this imaging plane can also be useful for cross-referencing brachial plexopathy abnormalities distal to roots and trunks. Traversing branches (solid arrows) are seen lateral to lateral border of pectoralis minor muscle (open arrow).
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Traumatic and Nontraumatic Causes of Brachial Plexopathy
A
B
C
Fig. 2—Anatomy of brachial plexus: trunks through branches. A, Illustration shows trunks (blue) positioned between anterior and middle scalene muscles, divisions (turquoise) lateral to scalene muscles and above clavicle, cords (pink) inferior to clavicle, and branches (magenta) lateral to expected location of lateral margin of pectoralis minor muscle. (Drawing by Toye CM) B and C, Coronal proton density–weighted (B) and coronal T1-weighted (C) MR images show that coronal plane is best for seeing more distal components of brachial plexus. In these images, trucks (solid white arrow, B), divisions (open arrow, B), cords (solid black arrow, B), and branches (arrows, C) are identified. Subclavian and axillary arteries (asterisks) are shown.
A
B
Fig. 3—Sagittal plane is helpful for further evaluation and problem solving. A, Sagittal T1-weighted MR image shows three individual cords—medial (open arrow), lateral (solid white arrow), and posterior (black arrow)—that are adjacent to subclavian artery (asterisk). B, More lateral MR image from same series as A shows branches (arrows).
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Tharin et al.
A
B Fig. 4—Orientation of imaging planes. A–C, Localizer MR images show how oblique alignment (lines) is set for axial (A), coronal (B), and sagittal (C) images of brachial plexus.
C
A Fig. 5—18-year-old woman with weak shoulder abduction, extension, and external rotation. A, Axial gradient-echo MR image shows schwannoma is affecting C5 postganglionic root (solid white arrow) and continues into more distal trunk (open arrow). B, Coronal STIR MR image shows trunk involvement (arrow) to better advantage than A.
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Fig. 6—62-year-old man with lung adenocarcinoma who presented with weakness in hand muscles. On this coronal T1-weighted contrast-enhanced MR image, mass (open arrow) is seen invading through pleura and affecting T1 nerve postganglionic root (solid white arrow), resulting in weakness in intrinsic muscles of hand.
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Traumatic and Nontraumatic Causes of Brachial Plexopathy
A
B
C
Fig. 7—33-year-old woman with left arm weakness. A, Radiograph shows bilateral (left larger than right) cervical ribs (arrows). B, Preoperative coronal T1-weighted MR image shows left cervical rib (thin arrow) is causing mass effect on distal trunks and proximal cords (thick arrow). C, Postoperative coronal T1-weighted MR image shows that cords (arrow) are no longer impinged by rib. Left arm weakness resolved. Fig. 8—Coronal fat-suppressed T2-weighted MR image of patient with cancer shows thickening and increased signal intensity (arrows) of left brachial plexus within radiation field. (Reprinted with permission of Anderson Publishing, Ltd., from Lury K., Castillo M. Imaging of the brachial plexus. Appl Radiol 2004; 4:28-32)
A
B
Fig. 9—Obstetric brachial plexopathy with resulting Erb palsy in 9-year-old girl. (Courtesy of Carlson CL, San Antonio Medical Center, Fort Sam Houston, TX) A, Three-dimensional reformation of thoracic CT, posterior view, shows ipsilateral scapula elevation (thick arrow) and anterior rotation as well as hypoplastic and dysplastic glenoid and humeral head (thin arrow). B, Sagittal T1-weighted MR image shows moderate atrophy of supraspinatus, infraspinatus, and subscapularis (arrows) muscles.
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Tharin et al.
Fig. 10—38-year-old man who sustained injuries from motorcycle crash. Coronal CT angiogram of neck obtained at time of injury shows left-sided hematoma (thin arrow) lateral to scalene muscles and in vicinity of subclavian artery. This finding should raise concern about mass effect of brachial plexus divisions and cords. Unaffected right side (thick arrow) is included for comparison.
A
Fig. 11—30-year-old man who presented with right upper extremity weakness 4 months after motor vehicle crash. Axial T2-weighted MR image shows avulsed root (thin arrow) within traumatic pseudomeningocele (thick arrow).
B
Fig. 12—25-year-old woman who sustained gunshot wound to upper thorax. A, Axial T2-weighted MR image obtained with fat suppression shows increased signal intensity (open arrows) along course of projectile and hematoma (solid white arrow) adjacent to cords (black arrow). B, Coronal STIR MR image shows edema and hematoma (thick arrow) surrounding cords and proximal branches (thin arrow). Surgical exploration to decompress hematoma before mass effect causes deafferentation should be considered in cases like this one.
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Fig. 13—38-year-old man with left brachial plexopathy after motor vehicle collision. Coronal STIR MR image shows increased signal intensity in left C6 root and superior trunk (arrow) consistent with stretch injury. Preganglionic root (not shown) was intact.
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Traumatic and Nontraumatic Causes of Brachial Plexopathy
A
B
Fig. 14—26-year-old man who sustained gunshot wound. Patient presented 3 weeks after injury with right upper extremity pain and weakness; at that time, CT myelography was performed because patient was unable to undergo evaluation with MRI given proximity of bullet to spinal cord. A, Sagittal CT myelogram shows that instilled intrathecal (solid black arrow) contrast material is in epidural space (open arrow) in cervical spine. This finding indicates dural disruption and raises suspicion for root avulsion. Beam-hardening artifact (white arrow) from adjacent bullet is noted. B, Axial CT myelogram provides further evidence of right root avulsion including spinal cord compression and displacement (straight solid arrow) to contralateral side, given absence of traction from injured nerve root; compression from epidural fluid and hemorrhage (open arrow); and pseudomeningocele (curved arrow). Arrowhead = surgical drain.
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