Tumor of the Nerves in Dogs

Peripheral nerve sheath tumors represent 25% of canine nervous system tumors and are most commonly diagnosed in middle age to older dogs. They can form in any location, from any peripheral nerve. Lesions of the peripheral nerves can be benign (schwannoma, neurofibroma), or malignant (usually a locally aggressive tumor that does not metastasize through the lymphatic system).

Tumors of the nerves are abnormal growths that originate from peripheral nerves or along the nerve sheath (myelin surrounding the nerves). In canines, the most common places a tumor of the nerves will be found are at the head and neck (cranial), the paraspinal region of the trunk (next to the spine), and the brachial plexus (a network of nerves found near the neck, shoulder and limb).

Symptoms of the presence of a tumor depend on the location. Below is a list of usual symptoms:

Brachial plexus and cervical nerve roots

• Pain in front limb
• Continual muscle weakness or lameness in thoracic limb (forelimb)
• Horner syndrome (sunken eye known as enophthalmia, droopy upper eyelid which is called ptosis, small pupil also called miosis, and evidence of prominent 3rd eyelid)
• Absence of ipsilateral cutaneous trunci reflexes (branches of lumbar and thoracic spinal nerves)
• If the tumor is pressing, or fixed within the spinal cord you may see partial or complete paralysis of limb

Lumbosacral plexus

• Slow degeneration of muscles in hindlimb
• Unilateral lameness of the hindlimb

Trigeminal nerve

• Absence of sensation in face
• Tumors can be painless or painful
• Degeneration of the mastication (for chewing) muscles

You pet may also exhibit neurological symptoms that are related to spinal nerve disruption (in relation to mobility, movement and control of limbs).

While the exact cause for tumors in the nerves in dogs has not yet been pinpointed, documentation shows that the following factors have been suspected:

• Previous exposure to radiation may bring about a tumor
• A hereditary mutation may be an explanation for a tumor
• Tumors have been seen to develop around a preceding injury

If you notice mobility issues, lameness, or any other sign that your dog is unwell, prompt attention by a veterinary professional is crucial. Our pets are unable to clearly express pain or illness and often try to continue on a day to day existence even though they are uncomfortable.

Schedule a visit and see the veterinarian promptly if you have concerns about a possible tumor. Documentation states that a tumor can be identified with the following elements in place:

• It arises from a peripheral nerve
• There are features in the cells and tissues such as protein binding
• The lesion develops from a pre-existing benign or malignant mass

The veterinarian will want to start with a complete physical, and at times a mass can be felt. In many instances, though, the tumor is not immediately found. The next step will be a complete blood profile, count, and chemistry.

A nerve biopsy may be suggested, as well as the tests listed below with their function:

• MRI or CT scan can accurately diagnose the presence of a tumor (the dog will need to be sedated for the procedure)
• Ultrasound cannot always identify small masses but is very beneficial when locating a larger size tumor because of echogenicity (ultrasound waves bounce off of affected nerves very well and can differentiate from unaffected nerves); also sedation is not usually required, so the procedure is easily repeated when needed
• Electromyogram can show abnormal muscle activity
• Myelography can accurately place the location of the mass
• Tomography can assess the whole spinal cord and vertebral column, and can identify if the spine is compressed

Surgical removal of the mass is typically the treatment of choice; this decision is based on whether the tumor is accessible and can be removed in it’s entirety. Regrettably, tumors of the nerves often advance beyond surgical margins before they are identified.

Surgery, if attempted, is sometimes accompanied by hemilaminectomy. This is a procedure that removes part of the vertebra in order to relieve pressure on nerve tissue, and can also involve removal of nerve roots at the spinal cord.

Complete amputation of a limb containing a tumor is a form of treatment also, but is done specifically when veterinary surgeons feel that they can totally eradicate the mass. Radiation therapy usually accompanies the above treatment protocols.

If the tumor can be completely removed, the prognosis is much more positive. Sadly, recurrence is common, especially in cases of nerve sheath tumors in the spinal cord. Tumors in the outer locations of the nerves allow for a better prognosis than a mass in the plexus (within the network of nerves) or root.

Less success is achieved if the tumor is not completely removed, or if the neurological damage remaining is severe, which can lower the quality of life for your dog and for you as a pet owner.

It must be noted that many dogs who have tumors in the nerves face recurrence or are euthanized due to a poor prognosis of recovery. However, a benign tumor of the peripheral type (outside or in the outer locations of the nerves) can have a good chance of eradication, leading to a positive outcome. The veterinarian will be an advocate for your pet, sincerely advising you on the wisest choice for the best outcome. Veterinarian care pushes the health and comfort of your dog first and foremost, which is why it's essential to listen to the advice and medical suggestion of the veterinarian.