An acoustic neuroma is a benign tumor found on the vestibular cochlear nerve, the nerve that connects the ear to the brain. This nerve is behind the ear, right under the brain.
A type of auditory tumor, an acoustic neuroma is also known as a vestibular schwannoma. This type of tumor is usually slow-growing and, although it does not affect brain tissue as cancerous tumors do, it may press against the nerves controlling hearing and balance as it grows. An acoustic neuroma is an uncommon cause of hearing loss. Many patients do not experience any problems from this type of tumor because it may remain very small, but if enlarges enough to exert serious pressure on the brain, it may become life-threatening.
Causes of an Acoustic Neuroma
Most of the time, the cause of an acoustic neuroma is unknown. If acoustic neuromas develop in both auditory nerves, the underlying cause may be a heredity disorder known as neurofibromatosis type 2, but this genetic defect accounts for only a very small percentage of cases. The great majority of acoustic neuromas are known as sporadic form, of no known origin. The one clear risk factor for this disorder is exposure to high doses of radiation.
Symptoms of an Acoustic Neuroma
As long as an acoustic neuroma remains small, the patient is usually asymptomatic. As it grows, however, and presses against the hearing and balance nerves, the patient will begin to show symptoms, which may become more severe as the tumor increases in size. These symptoms include the following:
- Loss of hearing in one ear
- Balance problems
- Ringing in the ears, also known as tinnitus
- Taste changes
Less commonly, patients with an acoustic neuroma may experience pain in one ear or on the face, or weakness of facial muscles. In extreme cases, if left untreated, an acoustic neuroma can eventually cause pressure on the brain, producing much more serious symptoms including confusion, numbness, facial paralysis and permanent hearing loss.
Diagnosis of an Acoustic Neuroma
A physical examination as well as the following diagnostic tests may be administered to detect the presence of an acoustic neuroma:
- Hearing test
- Auditory brain stem response (ABR)
- Electronystagmography (ENG)
- Head MRI scan
- Head CT scan
An ENG checks the effectiveness of the eyes, brain and middle ears and how these systems function while patients participate in various exercises to test their balance and move into different positions.
Treatment of an Acoustic Neuroma
When an acoustic neuroma remains small, the patient may only need regular heckups and evaluations of the tumor's growth. If the tumor has increased in size to the point that it interferes with normal functioning, radiosurgery may be required. In radiosurgery, radiation is focused on the site of the tumor to stop its growth. Radiosurgery allows the tumor to be removed without incision, protecting against damage to adjacent brain tissue. When acoustic neuromas are large, regular surgery may be used to prevent them from causing permanent damage.
There are risks associated with both radiosurgery and regular surgery for treatment of an acoustic tumor. With radiosurgery, risks may include partial or total hearing loss in the affected ear, permanent dizziness, facial paralysis or brain swelling. As with other forms of radiation, there is a chance that a malignancy may reoccur.