A PSNT is a benign or malignant tumor of peripheral nerve cell origin. Nerve sheath tumors may affect peripheral nerves, spinal nerve roots, or cranial nerves. Approximately 80% of nerve sheath tumors occur in the brachial plexus region. The remaining 20% involve cranial nerves or other spinal nerve roots. The trigeminal nerve is the most common cranial nerve affected. PNST are more common in dogs than cats. The exact cause of them are unknown.
There are many different types of PNST:
- Peripheral neuroblastoma
- Peripheral nerve sheath tumors
- Benign peripheral nerve sheath tumors
- Malignant peripheral nerve sheath tumors
- Malignant schwannoma
Symptoms typically include a combination of :
- Chronic, progressive lameness or weakness
- Muscle atrophy
- Aataxia (wobbliness)
- Proprioceptive deficits (knuckling)
- Decreased spinal reflexes
- Sensory deficits
A diagnosis is made by identify the tumor with advanced imaging (usually MRI) and/or obtaining a biopsy of abnormal tissue for histopathology. Other imaging tests such as chest radiographs and an abdominal ultrasound may be recommended to look for spread of the tumor.
Definitive treatment will consist of a combination of surgery, radiation therapy and chemotherapy depending the tumor type and likelihood of spread. Symptomatic treatment with anti inflammatory and pain medications will also be recommended.
The prognosis will depend on numerous factors (histopathologic grade, surgical accessibility, and stage). When the tumor is located distally in the limb away from the spinal cord surgery (amputation) can be curative at times. For tumors in close proximity to the spinal cord, the median postoperative survival time is 5-6 months, with a disease-free interval of about 1 month. Survival times of untreated trigeminal nerve sheath tumors ranged from 5 to 21 months.