Nerve Sheath Tumor in Dogs

Schwannoma in Dogs

Schwannomas are tumors that originate in the myelin sheath. The myelin sheath is produced by the Schwann cell, a specialized cell which surrounds the peripheral nerves, providing mechanical and physical support for the nerves as well as insulating the nerves that transmit the nervous system’s electrical signals. The peripheral nervous system consists of the nerves outside of the central nervous system (brain and spine). Peripheral nerve sheath tumor is the term that has been proposed to include schwannomas, neurofibromas (nerve fiber tumors), neurofibrosarcomas (malignant nerve fiber tumors), and hemangiopericytoma (tumor of blood vessels and soft tissue), since they are all believed to arise from the same cell type.

Symptoms and Types

• Chronic, progressive forelimb lameness and muscle atrophy
• Lameness in the hind limbs
• Peripheral nerve disorder (from self-mutilation)
• Palpable mass (mass can be felt by touch examination)
• Horner's syndrome, a disease of the sympathetic nervous system: automatic nerve reaction, affects parts of the body not under direct control
• If the Schwannoma is in the neck, only one side of the face will be affected:
  • Droopy eyelid
  • One sided facial paralysis
  • Decreased pupil size
  • Slight elevation of the lower eyelid

Causes

• Idiopathic (unknown)

Diagnosis

Your veterinarian will perform a complete physical exam on your dog, including a blood chemical profile, a complete blood count, a urinalysis and an electrolyte panel. You will need to provide a thorough history of your dog's health leading up to the onset of symptoms. A computed tomography (CT) or, ideally, a magnetic resonance imaging (MRI) can provide the most information regarding the extent and location of the disease. An electromyogram (a measurement of muscle activity) will show abnormal muscle activity if there is a schwannoma present.

Treatment

The treatment of choice is surgical removal (excision) of the tumor. Amputation of the affected limb is usually necessary, and local recurrence after surgery is common. A laminectomy (surgery of the spine to relieve pressure) is indicated with a schwannoma involving the nerve roots. Radiotherapy may be helpful, dependent on how far the growth has gone, and should be discussed with your veterinarian.

Living and Management

After surgical excision of schwannoma, 72 percent of all cases will have a recurrence. If this type of tumor affects the limb, the closer to the paw the schwannoma is, the easier it will be to treat. Schwannomas only rarely spread to the regional lymph nodes or to the lungs, staying mainly in the nerve cells.