MRI of the canine brachial plexus for peripheral nerve sheath tumours

When thoracic limb lameness is neurological

Thoracic limb lameness is usually orthopaedic. As a review of neurological causes of thoracic limb lameness (Kerwin and Taylor, Veterinary Clinics of North America: Small Animal Practice, 2021) sets out, several neurological diseases also cause it:

• lateralised intervertebral disc extrusion
• caudal cervical spondylomyelopathy
• brachial plexus avulsion
• neuritis
• peripheral nerve sheath tumours (PNSTs)

Many of these compress or destroy the nerve roots of the cervical intumescence and produce a non-weight-bearing lameness, or root signature. Advanced imaging such as MRI is needed to find the cause.

Lameness from a nerve tumour is not always weakness. In one dog with a malignant tumour of the median nerve (Smith et al., Frontiers in Veterinary Science, 2025), the lameness resolved after resection, which the authors attribute to neuropathic pain rather than paresis.

Not every lesion in this region is a tumour. In another dog (Andruzzi et al., Journal of Veterinary Internal Medicine, 2021), a chronic brachial artery thrombus caused episodic non-weight-bearing lameness, limb atrophy, cool paw pads and a painful axilla. It mimicked a nerve sheath tumour and was confirmed with MRI, CT, ultrasound and surgery.

Where these tumours occur

• In 44 dogs with histologically confirmed spinal PNSTs (Morabito et al., Journal of Veterinary Internal Medicine, 2023), the brachial plexus (C6–T2) was the most common site (18 of 44). Median age was 9 years, and lameness was the most common reason for referral (20 of 44).
• In 30 dogs with presumptive or confirmed nerve sheath tumours (Cooper-Khan et al., Veterinary Sciences, 2024), 22 involved spinal nerves, mostly of the brachial plexus, and 13 of these invaded the spinal canal. Survival was generally longer without spinal canal or intracranial involvement.
• In nine dogs operated on for brachial plexus tumours extending into the vertebral canal (Potamopoulou et al., Veterinary Surgery, 2024), the eighth cervical nerve root was affected in seven.

Brachial plexus MRI protocol at a glance

Some brachial plexus tumours are hard to detect, so a study of 18 dogs with brachial plexus PNSTs (Kraft et al., Veterinary Radiology & Ultrasound, 2007) calls for a rigorous multiplanar, multi-sequence examination. Its key principles are transverse images that include both axillae and the vertebral canal in the same slice, so lesions show up as asymmetry, and contrast, which was critical for subtle disease and full extent. The 44-dog study used STIR first to find affected nerves, and noted its value on low-field scanners.

What the radiologist looks at

In the 18-dog study:

• 8 had diffuse thickening of one or more plexus nerves, extending into the vertebral canal in 6
• 10 had a nodule or mass in the axilla; seven of these also had diffuse nerve sheath thickening, which reached the vertebral canal in 3
• most tumours were hyperintense to muscle on T2-weighted images and isointense on T1-weighted images
• 8 enhanced only minimally to mildly, and 13 enhanced heterogeneously

In the 44-dog study, most tumours involved both the vertebral canal and the peripheral nerve, and only 8 had a dumbbell shape. Muscle atrophy was seen in 40 of 44. No tumour caused vertebral lysis, but 34 showed mild bony changes consistent with pressure atrophy.

The reader compares the two sides for asymmetry of nerves and muscles, follows the affected nerves towards the foramina and vertebral canal, and states how far the disease extends. Imaging is weaker on grade:

MRI finding	Association with histological grade (44-dog study)
Large tumour volume	Grade 3 larger than grade 1
Peripheral contrast enhancement	Most frequent in grade 3 (62.5%)
Homogeneous enhancement	Most frequent in grades 1 and 2
Muscle atrophy, heterogeneous signal, growth into the vertebral canal	Not associated with grade

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. Neurology reporting covers CT and MRI. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• Use the extent map for treatment planning. In 30 dogs with malignant PNSTs of the brachial or lumbosacral plexus treated surgically (Stokes et al., Veterinary and Comparative Oncology, 2023), 13 needed a laminectomy as well as amputation or hemipelvectomy. Margins were complete (R0) in 12, recurrence occurred in 13 (46%), and median disease-specific survival was 570 days.
• Expect recurrence to be a risk even with aggressive surgery. In the nine dogs treated with combined forequarter amputation and hemilaminectomy, four were euthanised for suspected recurrence.
• Grade needs histology. Grade was difficult to identify from imaging alone, and in the 30-dog series, 25 diagnoses were presumptive rather than histologically confirmed.
• Talking to the owner: spinal canal or intracranial involvement matters for outlook, because survival was generally longer without it.

What to include when you request a brachial plexus MRI report

• signalment: age, breed and sex
• duration and progression of the lameness, and whether the dog bears weight
• pain on palpation of the axilla or limb, and muscle atrophy
• neurological examination findings in the affected limb
• orthopaedic work-up already done and its results
• whether surgery or radiotherapy is being considered, so extent is reported in the detail treatment needs

How Veheri can help

Veheri provides veterinary teleradiology and teleneurology and reports MRI studies of the brachial plexus remotely for clinics. For other neurological presentations, see when veterinary MRI is the right move, and for a differential named above, MRI of the canine cervical spine for cervical spondylomyelopathy.