Vestibular Schwannoma Health Article

Definition

A vestibular schwannoma is a type of benign (non-cancerous) tumor that affects the eighth cranial nerve.

Description

The eighth cranial nerve is involved in both hearing (the auditory or acoustic component of the nerve) and balance (the vestibular component of the nerve). Like all cranial nerves, the eighth cranial nerve (also called the acoustic or auditory nerve) is paired, meaning that there is one on each side of the body. Each eighth cranial nerve runs from the inner ear to the brain, passing through a bony canal called the internal auditory canal. This canal is shared with the seventh cranial nerve, the facial nerve.

Like many nerve fibers, the eighth cranial nerve is wrapped in a sheath composed of specialized Schwann cells that serve to speed the transmission of information along the nerve. When the Schwann cells grow in an uncontrolled fashion, they can develop into a tumor, called schwannoma or neuroma. Although a vestibular schwannoma is not malignant (cancerous), it can still result in serious symptoms caused by pressure on the eighth cranial nerve or on surrounding tissues or the adjacent facial nerve. Most cases of vestibular schwannoma are unilateral; that is, only one of the two eighth cranial nerves is affected.

Demographics

About 100,000 people in the United States develop vestibular schwannoma. Most people who develop a vestibular schwannoma are between the ages of 30 and 50; children rarely develop vestibular schwannoma. Women are slightly more likely than men to develop a vestibular schwannoma.

There is an increased risk of developing a vestibular schwannoma in individuals who have a disease called neurofibromatosis. In these cases, the tumors tend to develop on both sides (bilaterally). In fact, about 10% of all cases of vestibular schwannoma occur in individuals who have neurofibromatosis. People with neurofibromatosis who develop vestibular schwannoma may do so at a younger age, sometimes in their teens or early adulthood.

Causes and symptoms

No one knows exactly why some people develop a vestibular schwannoma. Most seem to occur sporadically, with no identifiable cause. There is an increased risk of developing a vestibular schwannoma in individuals with neurofibromatosis, and some research has suggested that individuals who are chronically exposed to loud noise may have an increased risk of developing a vestibular schwannoma.

The initial symptoms of vestibular schwannoma are caused by pressure on the eighth cranial nerve, and include gradually progressive one-sided hearing loss, buzzing in the ears (tinnitus), dizziness, and difficulty with balance. In particular, the hearing impairment greatly affects the ability to understand speech (speech discrimination). When the vestibular schwannoma puts pressure on the seventh cranial nerve, pain and numbness in the face may develop. Eventually, the facial muscles may become paralyzed. The individual may also experience difficulty chewing and/or swallowing, ear pain, and headache. When left untreated, hearing impairment may eventually lead to complete deafness in the affected ear. If the tumor begins to encroach on other brain tissues, the person may experience nausea, vomiting, fever, vision changes, and difficulty walking.

Diagnosis

A careful neurologic examination will reveal the deficits that are characteristic of vestibular schwannoma. Computed tomography (CT) or magnetic resonance imagaing (MRI) scan may help pinpoint the tumor. Audiometry and brain stem auditory evoked potential tests are performed to establish the degree of hearing deficit prior to treatment. Audiometry assesses hearing acuity by evaluating the ability to hear various volumes and tones. A brain stem auditory evoked potential test evaluates brain wave responses to clicking sounds, in order to assess the functioning of the auditory (hearing) pathways in the brain.

Treatment team

When an individual is suspected of having a vestibular schwannoma, an otorhinolaryngologist and/or neurologist may be consulted to arrive at a diagnosis. An otorhinolaryngologist will be called upon if surgery is required.