These tumors are thought to arise when there is a defect in a certain tumor suppressor gene, which normally prevents tumors from occurring. The cause of the genetic defect is not known. However, acoustic neuroma is often linked with the genetic disorder neurofibromatosis type 2 (NF2).

Acoustic neuromas are relatively uncommon in general, but they are one of the most common types of brain tumors. They affect approximately 1 out of 100,000 people per year.

The tumor is most commonly located at the base of the brain, where the auditory nerve leaves the skull cavity and enters the bony structure of the inner ear.

Symptoms of Acoustic neuroma

The cause of acoustic neuroma is unknown. The symptoms develop over several years as the tumor slowly grows and pushes on surrounding structures. The first problem is usually ringing in the ears (tinnitus), decreased hearing, and dizziness (vertigo). As the tumor grows, other symptoms appear such as pain around the ear, imbalance, loss of coordination, and facial twitching, drooping or numbness. Later on headache and vomiting may develop.

Common symptoms include:

• tinnitus (ringing) in the affected ear
• hearing loss in the affected ear
• vertigo (an abnormal sensation of movement)

Less common symptoms include:

• headache
  • upon awakening in the morning
  • which awakens patient from sleep
  • aggravated by lying down, reclining position
  • aggravated by standing up
  • aggravated by coughing, sneezing, straining, lifting (Valsalva maneuver)
  • with nausea or vomiting
• difficulty understanding speech (out of proportion to total hearing loss)
• dizziness
• loss of balance
• numbness in the face or one ear
• pain in the face or one ear
• transient vision abnormalities

Diagnosis of Acoustic neuroma

• facial drooping on one side
• unsteady walk
• drooling

Patients with an acoustic neuroma will usually seek medical attention because of hearing problems. A hearing test (audiogram) is often abnormal. After that, several other tests of the balance and hearing systems will identify the problem. Some of these tests, like flushing the ear with cold water to stimulate the vestibular system, can be done in the physician's office. Other tests, like magnetic resonance imaging (MRI) scans and brainstem auditory evoked potentials (BAEPs) require specialized facilities. Patients with neurofibromatosis (von Recklinghausen's disease) are far more likely to have an acoustic neuroma as the cause of their hearing problem.

Treatment of Acoustic neuroma

Surgery

• Goals of surgical treatment are removal of the tumor and prevention of facial paralysis. Preservation of hearing is more difficult. If a tumor is removed when it is very small, hearing may be preserved. Any hearing that is lost prior to surgery will not be regained. Large tumors usually result in total loss of hearing on the affected side.
• Large tumors may also compress nerves important for facial movement and sensation. These tumors can typically be safely removed, but the surgery often results in paralysis of some facial muscles.
• Extremely large tumors may additionally compress the brainstem, threatening other cranial nerves and preventing the normal flow of cerebrospinal fluid. This can lead to a build-up of fluid in the head (hydrocephalus) which can cause potentially life-threatening increased intracranial pressure. Goals of surgery in these cases are treatment of the hydrocephalus and decompression of the brainstem.

Stereotactic radiosurgery

• The goal of radiation therapy is to slow or stop the tumor growth, not to cure or remove the tumor.
• Radiosurgery is often performed in elderly or sick patients who are unable to tolerate brain surgery.
• Sometimes during brain surgery to treat acoustic neuromas, not all of the tumor can be safely removed, and some residual tumor must be left behind. Radiosurgery is often used post-operatively to treat residual tumor in these cases.
• Radiosurgery is only appropriate for small tumors, so that radiation damage to surrounding tissues can be minimized.
• Like brain surgery, radiosurgery can sometimes result in facial paralysis or loss of hearing.

Observation

• Since these tumors usually grow very slowly, small tumors that have minimal or no symptoms (asymptomatic) can be safely observed with regular MRI scans and left untreated unless they grow dangerously.
• Very often elderly patients will die of other natural causes before small, slow growing tumors become symptomatic.