What Causes Nerve Sheath Tumors?

Nerve sheath tumors are the tumors of the nerve sheath, which is the covering of nerve fibers that help in transmitting messages across the nervous system involving the brain and the spinal cord to the rest of the body. Nerve sheath tumors are classified into benign and malignant types. The examples of benign tumor includes Schwannomas and neurofibromas, whereas, neurofibrosarcoma is an example of a malignant tumor.

What Causes Nerve Sheath Tumors?

What Causes Nerve Sheath Tumors?

Causes of nerve sheath tumors, for the most part, are unknown. However, neurofibromas and schwannomas, which are benign peripheral nerve tumors, are known to be caused by conditions known as schwannomatosis and neurofibromatosis (type 1 and type 2). Schwannomatosis and neurofibromatosis are both inherited conditions leading to tumor growth on nerves. Nerve sheath tumors are more common in people with neurofibromatosis type 1. Neurofibromatosis type 1 can cause multiple neurofibromas and sometimes malignant peripheral nerve sheath tumors. Vestibular schwannomas are linked with neurofibromatosis type 2. Some neurofibrosarcomas have an exposure to past radiation therapy.

Nerve sheath tumors affect people of all ages and both genders. Neurofibromatosis type 1 is usually seen between the ages of 30-40 years while malignant tumors are seen mostly between the ages of 40-50 years.

Patients with nerve sheath tumors present with few to no symptoms at all, until, the tumor presses or grows against the nerves. The signs and symptoms of nerve sheath tumors are either due to effects of the tumor on the primary nerve or from the nerve sheath tumor pressure on nearby blood vessels, tissues or nerves.

The symptoms of nerve sheath tumors include painless/painful growth, lump on the affected part of the body (such as the face, arms or legs), numbness, tingling, burning or having “pins and needle” sensation of the affected part of the body, weakness, loss of function of the affected muscles, and hearing loss, ringing in the ear, the loss of coordination and balance in the case of vestibular schwannoma.

Diagnosis And Treatment Of Nerve Sheath Tumors

The diagnosis of nerve sheath tumor is based on past medical history, clinical presentation and neurological and physical examination. Several tests help find the tumor size, location, type and cause of the signs and symptoms. These include MRI, CT scan, electromyography, nerve conduction study, tumor biopsy and nerve biopsy.

The treatment of nerve sheath tumor depends on the type of tumor, nerve or tissues affected along with the presenting symptoms. Benign tumors sometimes require no treatment, except monitoring for progression of symptoms, growth and spread. Surgery may be needed to treat a large tumor or a malignant tumor with the aim of removing the entire tumor preserving the healthy tissues and surrounding nerves. Radiation therapy may be needed after surgery to reduce the risk of recurrence or a high-dose radiation therapy may be needed when surgery is not possible. Adjuvant chemotherapy is also helpful along with radiation therapy.

The prognosis/outlook for nerve sheath tumor depends on the size, location and spread of the tumor. Usually, malignant tumors have a poorer prognosis than benign tumors.

The function of nerve sheath is protection and insulation of nerve fibers and enhancement of transmission of electrical impulses. It is made of Schwann cells that form the myelin sheath. Schwannomas form when the Schwann cells forming the myelin sheath grow abnormally. They mostly develop along nerves of the head and neck and a typical example of schwannoma is vestibular schwannoma also known as acoustic neuroma. Acoustic neuroma is a tumor affecting the nerve of the inner ear connecting to the brain.

Neurofibrosarcomas are tumors originating in nerves and are considered a part of soft tissue sarcomas. Neurofibrosarcomas are rarer than schwannomas and thus uncommon. They are mostly found in the arms and legs as opposed to schwannomas that are mostly found in the head and neck region; although, they can also be found in the head and neck region.

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