A vestibular schwannoma (also known as acoustic neuroma, acoustic neurinoma, or acoustic neurilemoma) is a benign, usually slow-growing tumor that develops from the balance and hearing nerves supplying the inner ear.
The tumor comes from an overproduction of Schwann cells–the cells that normally wrap around nerve fibers like onion skin to help support and insulate nerves. As the vestibular schwannoma grows, it presses against the hearing and balance nerves, usually causing:
- Unilateral (one-sided) or asymmetric hearing loss
- Tinnitus – ringing in the ear
- Dizziness/loss of balance
As the tumor grows, it can interfere with the face sensation nerve (the trigeminal nerve), causing facial numbness. Vestibular schwannomas can also press on the facial nerve (for the muscles of the face) causing facial weakness or paralysis on the side of the tumor. If the tumor becomes large, it will eventually press against nearby brain structures (such as the brainstem and the cerebellum), becoming life-threatening.
Unilateral vestibular schwannomas affect only one ear. They account for approximately 8 percent of all tumors inside the skull; one out of every 100,000 individuals per year develops a vestibular schwannoma. Symptoms may develop at any age but usually occur between the ages of 30 and 60 years. Unilateral vestibular schwannomas are not hereditary.
Bilateral vestibular schwannomas affect both hearing nerves and are usually associated with a genetic disorder called neurofibromatosis type 2 (NF 2). Half of affected individuals have inherited the disorder from an affected parent and half seem to have a mutation for the first time in their family. Each child of an affected parent has a 50 percent chance of inheriting the disorder. Unlike those with a unilateral vestibular schwannoma, individuals with NF2 usually develop symptoms in their teens or early adulthood. In addition, patients with NF2 usually develop multiple brain and spinal cord related tumors. They also can develop tumors of the nerves important for swallowing, speech, eye and facial movement, and facial sensation.
Scientists believe that both unilateral and bilateral vestibular schwannomas form following the loss of the function of a gene on chromosome 22, which produces a protein that controls the growth of Schwann cells.
Early diagnosis of a vestibular schwannoma is key to preventing its serious consequences. There are three options for managing a vestibular schwannoma:
- Surgical removal
- Radiation
- Monitoring
Typically, the tumor is surgically removed (excised). The exact type of operation done depends on the size of the tumor and the level of hearing in the affected ear. If the tumor is very small, hearing may be saved and accompanying symptoms may improve. As the tumor grows larger, surgical removal is more complicated because the tumor may have damaged the nerves that control facial movement, hearing, and balance and may also have affected other nerves and structures of the brain.