MRI findings in brachial plexus injury

Clinical History

A 41-year-old man was admitted to the emergency department with severe functional impairment of his left upper extremity after a blunt upper thoracic trauma.

Imaging Findings

A 41-year-old man was admitted to our emergency department because of an upper thoracic trauma he suffered at work. More specifically, a large, marble plate fell onto his chest and left shoulder and resulted in severe functional impairment of his left upper extremity. Physical examination confirmed the important neurologic deficit of the left arm.
The chest X-ray revealed a fracture in the middle portion of the left clavicle.
As there was a high clinical suspicion of brachial plexus injury, an MRI of the brachial plexus and cervical and thoracic spinal column was performed.
MRI revealed a pathologically increased signal intensity in the left supra- and infraclavicular space on STIR images, which was thought to be due to the traumatic injury of the region. The left clavicular fracture was also obvious. Furthermore, the left C7, C8 and T1 roots of the brachial plexus appeared oedematous and their nerve sheaths enhanced strongly after the intravenous administration of gadolinium. No CSF protrusion through the foramina of lower cervical and upper thoracic spinal column was present.
The combination of these MR findings were indicative of brachial plexus traumatic injury.
The patient also underwent a neurophysiologic examination, which was indicative of a probably irreversible damage of the left brachial plexus. No internal fixation of the clavicular fracture was done. After two months of hospitilisation and conservative treatment, the patient showed no clinical improvement, so he was transfered to a rehabilitation unit. He is scheduled for a new electrophysiologic study after a one month period.

Discussion

The brachial plexus is responsible for the innervation of the shoulder, upper extremity and upper thoracic muscles. In the cervicothoracobrachial region, it courses superior and posterior to the subclavian artery and vein. The brachial plexus consists of 5 segments: roots, trunks, divisions, cords and terminal branches. The supraclavicular plexus includes roots and trunks. The roots of the plexus are formed by the anterior rami of the C5-T1 nerve, with or without minor branches from C4 and T2. Through the neural foramina, roots of the plexus extend into the interscalene region, forming the superior (C5- C6), middle (C7) and inferior (C8-T1) trunks. The retroclavicular plexus includes the anterior and posterior division of the trunks. The infraclavicular plexus, situated in the retropectoralis minor space, includes the three cords (medial, lateral and posterior) and the terminal branches of the plexus (median, ulnar, musculocutaneous, axillary and radial nerves).
Brachial plexus injury (BPI) is the most severe nerve injury of the extremities, resulting in functional impairment of the upper limb. BPI is caused by severe traction force exerted on the upper limb, resulting in complete or partial motor paralysis. An upper brachial plexus lesion involves C5 and C6 nerves and leads to paralysis of the shoulder muscles and biceps. When the damage extends to C7 spinal nerve, some of the wrist muscles are also impaired. A lower brachial plexus injury involves spinal nerves C8 and T1 and induces paralysis of the forearm flexor and the intrinsic muscles of the hand. BPI is most common in neonates due to birth palsy and in adolescents due to car accidents or shoulder luxation.
BPI is classified into trhee categories: preganglionic lesions, postganglionic lesions and a combination of these two. A preganglionic lesion signifies avulsion of nerve roots, whereas a postganglionic lesion involves the nerve structures distal to the sensory ganglion. Postganglionic lesions are further classified into nerve ruptures and lesions in continuity.
MRI provides useful anatomic information on BPI. The most important MR findings in BPI include:
1) Signal intensity changes are observed in the spinal cord in approximately 20% of patients with preganglionic injuries. Hyperintense areas on T2WI suggest oedema in the acute phase and myelomalacia in the chronic phase. On the other hand, hypointense areas on T2WI reflect haemosiderin deposition due to old haemorrhage. Pseudomeningocele is also a common finding in preganglionic injuries; it is usually accompanied by root avulsion, but in 15% of cases it can occur without root avulsion.
2) Furthermore, enhancement of intradural nerve roots and root stumps suggests functional impairment of nerve roots, despite morphologic continuity. Breakdown of the blood-nerve barrier and dilatation of radicular veins are postulated as the mechanisms of this enhancement.
3) Abnormal enhancement of paraspinal muscles (especially the multifidus muscle) is considered to be an accurate, indirect sign of root avulsion injury. Denervated muscles show enhancement as early as 24 hours after a nerve is injured.
4) Another advantage of MRI is visualisation of the postganglionic brachial plexus. Oedema and fibrosis of the brachial plexus can manifest as thickening of the plexus.

Differential Diagnosis List

Final Diagnosis

Brachial plexus injury

URL:	https://www.eurorad.org/case/8629
DOI:	10.1594/EURORAD/CASE.8629
ISSN:	1563-4086