Page 387 - Atlas of Small Animal CT and MRI

Brachial and Lumbosacral Plexus 377

in the veterinary literature, there are few references to and may lick or chew the extremity because of abnormal
cross‐sectional imaging of the disorder. 4–8 sensation. Those PNST that involve the spinal nerves
CT myelography has been used in people for diagnosis proximal to their arborization into the plexus can extend
of preganglionic brachial plexus injury. Intact dorsal and to the spinal nerve roots and invade the spinal cord.
ventral nerve roots are seen as radiating linear filling Those PNST that include the T1 and T2 spinal nerves
defects in the contrast‐enhanced subarachnoid space, will have an intrathoracic or thoracic inlet component.
and avulsion is diagnosed based on an absence of this In a study describing CT features of brachial plexus
finding. Pseudomeningoceles are also indicative of neoplasms in dogs, consistent findings included
avulsion and appear as a focal dilation of the enhanced periscapular muscle atrophy, well‐defined axillary mass
subarachnoid space. CT myelography has been used for margins, and contrast enhancement of most masses,
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diagnosis of nerve root avulsion in a small case series of with peripheral distribution in about half. Over 25% of
dogs and cats. 4 masses extended proximally to the vertebral canal, and
MR features of postganglionic injuries in people approximately 25% extended into the thoracic cavity
include thickened nerves that are T1 hypointense, T2 (Figure 3.6.4). Although these features are consistent
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hyperintense and contrast enhance. Discontinuity of with our experience with brachial plexus PNST, only one
transected nerves may also be evident. Features of third of dogs had histologic confirmation of tumor type
preganglionic injuries include direct evidence of nerve in this study. In an investigation of MR features of
root avulsion from the spinal cord (Figure 3.6.3). A pseu­ brachial plexus PNST, findings included diffuse brachial
domeningocele, a focal dilatation of the arachnoid space, plexus nerve thickening or discrete axillary mass, T1
is often also present. Evidence of intrinsic spinal cord isointensity and T2 hyperintensity compared to muscle,
disease can also be seen. MR imaging following intra­ and variable and often heterogeneous contrast enhance­
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thecal administration of contrast medium has been used ment (Figures 3.6.5, 3.6.6). Muscle atrophy and signal
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to detect traumatic dural tears associated with avulsion changes associated with muscle denervation (described
injury in a dog. 5 above) are also often present. It can be helpful to begin
an MR imaging study of suspected brachial plexus
Inflammatory disorders neoplasia with a dorsal plane, large field‐of‐view STIR
sequence to localize the lesion as focal or regional
Brachial plexus neuritis is rare but has been reported in hyperintensity.
the veterinary literature. In people, MR features of bra­ Imaging features of lumbosacral plexus PNST are
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chial plexus neuritis include diffuse nerve enlargement, similar to those of brachial plexus tumors (Figures 3.6.7,
T2 hyperintensity, and variable contrast enhancement. 12
3.6.8).
Neoplasia Other neoplasms

Peripheral nerve sheath tumors Other neoplasms affecting the brachial and lumbar
Peripheral nerve sheath tumors (PNST) can be either plexus are rare but include lymphoma, hemangiosar­
benign or malignant and account for the vast majority coma, other sarcomas, and a variety of other tumors.
of neoplasms of the brachial and lumbosacral plexus Although CT and MR imaging descriptions are lacking,
in dogs and cats. The veterinary literature and experience our experience is that lymphoma can appear similar to
suggest that PNST are more common in the brachial and is not reliably distinguishable from PNST
plexus. 13–16 Clinical signs of brachial plexus PNST include (Figure 3.6.9). Lipomas frequently arise in the axillary
unilateral forelimb lameness and muscle atrophy. Affected region and can displace or incorporate nerves of the bra­
animals may also show signs of pain on limb manipulation chial plexus (Figure 3.6.10).

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