Brachial plexus injuries

Brachial plexus injuries are a spectrum of upper limb neurological deficits secondary to partial or complete injury to the brachial plexus, which provides the nerve supply of upper limb muscles. 

Clinical presentation

Trauma, usually by motor vehicle accidents, involves severe traction on the upper limb which leads to partial or complete nerve avulsion:

• C5/C6 involvement leads to paralysis of shoulder and biceps muscles
• C7 is involved, paralysis extends to wrist and hand muscles
• C8/T1 involvement leads to paralysis of the forearm flexors and hand intrinsic muscles

Also, birth (obstetric) injuries can involves the upper trunk leading to an Erb palsy.

Classification

In the simplest form, brachial plexus injuries can be classified as preganglionic or postganglionic however in clinical practice they can be mixed ¹. Each injury has very different management and prognosis.

• preganglionic
  • injury proximalto the dorsal root ganglion therefore affecting the CNS which does not have the capacity to regenerate
  • e.g. nerve root avulsion
• postganglionic
  • distalto the dorsal root ganglion affecting the PNS which does have some capacity to regenerate
  • e.g. nerve ruptures and lesions in continuity ¹

Brachial plexus injuries can also be more specifically classified into six types by CT myelography.

Radiographic features

Conventional (fluoroscopic) myelography

Conventional myelography is performed via intrathecal injection of iodinated contrast media. Nerve roots can be demonstrated as well as the leakage of contrast into the meningocoele. 

Advantages include high spatial resolution and absence of CSF flow artefacts. Disadvantages include improper filling of the meningocoele sac in the presence of dural scar, intra and post procedural complications e.g. hematoma, infection, allergic reaction and headache. 

Nowadays myelography is almost always performed in conjunction with CT myelography.

CT myelography

Widely replaces conventional myelography as it utilizes less contrast agent and hence less contrast reaction. Advantages include ability to detect partial root avulsion, excellent visualization of bony structures, no CSF flow artifacts and multiplanar reconstruction. Disadvantages include high radiation dose, poor visualization of lower brachial plexus due to bony artefacts, pre- and post procedural complications.

Conventional MRI

Together with direct visualization of nerve root and sleeves, spinal cord injuries present as edema in acute stage and myelomalacia in chronic stage. In preganglionic injruy, there is usually an avulsion pseudomeningocoele, which is a CSF filled structure at the site of the nerve root that does not contain any neural elements. There may be associated cord hematoma. Post contrast enhancement of nerve root suggest functional impairment even if it appears continuous. Abnormal enhancement of paraspinal muscles is an indirect sign of root avulsion.

MR myelography

This uses steady state coherent gradient echo sequences which imply high contrast to noise ratio and reduce flow artefacts. It can easily identify nerve roots and meningocoele sac even if there are intradural scars.

Diffusion weighted neurography

A recent modality which can demonstrate postganglionic injuries as discontinuation of injured nerves.

Treatment and prognosis

Depends on the site of injury and degrees of damage ¹. Preganglionic injury is repaired by nerve transfer (usually an intercostal nerve) to the denervated muscles, as there is no chance of spontaneous neural repair. Postganglionic injury is treated conservatively or with nerve grafting, where a nerve autograft is sutured between the excised damaged nerve segment.