Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

MINI-SYMPOSIA-HEAD AND NECK
Year
: 2012  |  Volume : 22  |  Issue : 4  |  Page : 344--349

Pictorial essay: Role of magnetic resonance imaging in evaluation of brachial plexus pathologies


Malini Lawande, Deepak P Patkar, Sona Pungavkar 
 Department of MRI, Dr. Balabhai Nanavati Hospital, Mumbai, India

Correspondence Address:
Malini Lawande
5A, Shimpla Vignaharta Scty, 35, Juhu Versova Link Road, Andheri West, Mumbai - 400 053
India

Abstract

Brachial plexopathies, traumatic and nontraumatic, often present with vague symptoms. Clinical examination and electrophysiological studies are useful but may not localize the lesion accurately. Magnetic resonance imaging (MRI) with its multiplanar imaging capability and soft tissue contrast resolution plays an important role in evaluation of the abnormal brachial plexus.



How to cite this article:
Lawande M, Patkar DP, Pungavkar S. Pictorial essay: Role of magnetic resonance imaging in evaluation of brachial plexus pathologies.Indian J Radiol Imaging 2012;22:344-349


How to cite this URL:
Lawande M, Patkar DP, Pungavkar S. Pictorial essay: Role of magnetic resonance imaging in evaluation of brachial plexus pathologies. Indian J Radiol Imaging [serial online] 2012 [cited 2019 Nov 19 ];22:344-349
Available from: http://www.ijri.org/text.asp?2012/22/4/344/111489


Full Text

 Introduction



Brachial plexus is the main sensory and motor innervation of the upper extremity. It may be involved in a variety of traumatic and nontraumatic pathologies. MRI is useful both in diagnosis and in localization of these lesions. This makes a significant impact on the management.

Imaging of brachial plexus by MRI is challenging due to the large field of view to be covered with heterogeneous tissue distribution including fat, muscles, and bones.

Normal anatomy

The brachial plexus is formed by the ventral roots of C5 to T1 nerve roots. These unite to form three trunks. The trunks split into three anterior and three posterior divisions. These unite to form the three cords that further divide into five peripheral nerves. The roots and trunks are supraclavicular in location while divisions are retroclavicular and the cords are infraclavicular. [1],[2]

Imaging technique

The T1-weighted images delineate the anatomy of nerves, muscles, and vessels as they are outlined by fat, while the T2-weighted images reveal the signal abnormalities

within the brachial plexus. Short-tau inversion recovery (STIR) images provide uniform and reliable fat suppression over curved surfaces and large field of view [Figure 1]A and B. The scan protocol followed at our department consists of coronal STIR and T1-weighted images with large field of view (FOV), including both brachial plexi for comparison followed by sagittal T1-and T2-weighted images with small FOV for high spatial resolution. Intravenous Gadolinium is administered in patients with tumors or mass lesions. Gadolinium is not administered in patients with traumatic brachial plexopathy. In patients with traumatic brachial plexus injury, in addition to the previously described protocol, sagittal T2-weighted images are obtained through the cervical spine followed by axial T2-weighted images from C4 to T2 levels. In addition, a 3D gradient echo (GRE) sequence with thin slices is obtained to look for the nerve root avulsion.{Figure 1}

In patients suspected with thoracic outlet syndrome, in addition to coronal STIR and coronal T1-weighted images, sagittal T1-weighted images are obtained through the symptomatic side extending from midline to the axilla with arm in hyperabducted position. These are compared with similar sagittal T1-weighted images obtained with arm in neutral position by the side of body.

Traumatic injuries to brachial plexus

The common causes of brachial plexus injuries are road traffic accidents and birth palsy. Brachial plexus injuries can be divided into pre- and postganglionic lesions. The preganglionic lesions are avulsion of the nerve roots at their origin while postganglionic lesions may be lesions in continuity or nerve ruptures. The patient may have a combination of both pre- and postganglionic lesions. It is important to differentiate between pre and postganglionic lesions to determine the prognosis and plan further management. Postganglionic lesions in continuity without disruption of nerve fibers have good prognosis and recover spontaneously with conservative management. Postganglionic lesions with disruption of nerve fibers are treated with surgical repair, that is, nerve grafting with good results. Preganglionic lesions are usually treated with nerve transfers to restore function of the denervated muscles. [3],[4]

Pseudomeningoceles are formed due to extravasation of cerebrospinal fluid through tear of the perineural sheath. These are seen on T2-weighted images as fluid-intensity lesions at the site of nerve root avulsion [Figure 2]A and B. However, presence of a pseudomeningocele is not always seen in nerve root avulsion and vice versa.{Figure 2}

Neuropraxic injury is seen as T2 hyperintense signal in the roots, trunks, or cords with or without enlargement [Figure 3]A and B. Nerve ruptures are seen as discontinuity in the neural structures [Figure 4]A and B. [1] Associated findings of denervation edema in the muscles may be seen [Figure 5]A and B.{Figure 3}{Figure 4}{Figure 5}

Brachial plexus injuries may be associated with injuries to the subclavian artery due to their anatomical proximity to each other. Also post-traumatic pseudoaneurysm of subclavian artery may present with delayed brachial plexus paralysis due to compression of the brachial plexus [5] [Figure 6].{Figure 6}

 Nontraumatic Brachial Plexus Pathologies



Radiation fibrosis

Patients undergoing radiation therapy in axillary region, most commonly for breast carcinoma, may present with brachial plexopathy after several months to years. Radiation fibrosis is seen as diffuse thickening of the brachial plexus and iso- or hypointensity on T1- and T2-weighted images. The absence of a focal mass differentiates it from metastatic disease [Figure 7]A-C. Moreover, metastases appear hypointense on T1-weighted images and hyperintense on T2-weighted images. [6]{Figure 7}

Brachial plexus neuritis

Acute brachial plexitis presents with severe shoulder and upper arm pain lasting for few days to weeks followed by upper arm weakness. Idiopathic brachial neuritis is of unknown cause but an immune-mediated inflammatory reaction following viral infection, vaccination, surgery, pregnancy, etc., has been proposed as etiology .[7] Bilateral brachial plexus neuritis in postpartum period [Figure 8] has been described by Dumitru and Liles. [8] Brachial plexitis is seen on MRI as focal or diffuse hyperintense signal in brachial plexus.{Figure 8}

Brachial plexus tumors

Nerve sheath tumors (schwannoma and neurofibroma) are seen as ovoid lesions isointense to muscle on T1-weighted images and hyperintense on T2-weighted images with 'target' sign. These reveal intense enhancement on administration of gadolinium contrast.[Figure 9]A and B. Most common benign tumors that involve brachial plexus are lipomas and aggressive fibromatosis. [9],[10] Metastatic breast carcinoma [Figure 10]A-C, superior sulcus tumors (non-small-cell lung carcinoma arising from lung apex) [Figure 11]A and B, and lymphoma involve the brachial plexus frequently. [6]{Figure 9}{Figure 10}{Figure 11}

Thoracic outlet syndrome

It is dynamically induced compression of neural and/or arterial structures crossing the cervicothoracobrachial junction. MRI plays an important role in demonstrating neurovascular compression, localizing it and identifying the structure causing the compression. The three spaces that are evaluated on sagittal T1-weighted images are the interscalene triangle, costoclavicular, and retropectoralis minor spaces with arm in neutral as well as hyperabducted position to look for compression of the neurovascular structures [Figure 12],[Figure 13],[Figure 14] and [Figure 15]. The costoclavicular space is the most common site of compression followed by interscalene triangle. The lesions causing compression may be bony abnormalities (cervical rib [Figure 16] and [Figure 17], long transverse process of C7 vertebra, callus or osteochondroma of clavicle or first rib) or soft tissue pathologies (fibrous band, hypertrophy of scalenus anterior muscle, scalenus minimus muscle, and fibrous scarring). [11] Bilateral hypoplastic first ribs fused to second ribs can also cause thoracic outlet syndrome [Figure 18] and [Figure 19]. Contrast-enhanced MR angiography may be performed with the arm in elevated position to demonstrate narrowing of subclavian artery. Dymarkowski, et al., recommend performing 3D MR angiography with arm in adduction followed by arm in hyperabducted position. [12]{Figure 12}{Figure 13}{Figure 14}{Figure 15}{Figure 16}{Figure 17}{Figure 18}{Figure 19}

To summarize, brachial plexus has a complex anatomy and long course. Various traumatic and nontraumatic pathologies affecting it can be evaluated optimally by MRI. Knowledge of the anatomy and proper planning of the scan are essential for complete evaluation of the brachial plexus.

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