Acoustic neuroma

Definition

An acoustic neuroma is a benign, noncancerous, often slow-growing tumor of the nerve that connects the ear to the brain (8th cranial or auditory) nerve.

Alternative Names

Causes

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, 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

The symptoms vary with the size and location of the tumor. Because the tumors grow so slowly, symptoms usually arise after the age of 30.

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
  • Wakes patient from sleep
  • Worse when lying down, reclining position
  • Worse when standing up
  • Worse when 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

Exams and Tests

The health care provider may diagnose an acoustic neuroma based on the history, neurological examination or testing of the patient. The results of a physical examination are often unremarkable, except for the following signs:

• Facial drooping on one side
• Unsteady walk
• Drooling

If the tumor is large, there may additionally be signs of increased pressure on the brain (increased intracranial pressure

• Nausea and vomiting
• Unilateral (one side only) dilated pupil -- see eyes, pupils different size
• Sleepiness

The most useful (i.e., sensitive and specific) test to identify acoustic neuromas is an MRI of the head. Other useful tests used to diagnose acoustic neuroma and to differentiate it from other causes of dizziness or vertigo include:

• Head CT
• Audiology (a test for hearing)
• Caloric stimulation (a test for vertigo)
• Electronystagmography (a test of equilibrium and balance)
• Brainstem auditory evoked response (BAER, a test of hearing and brainstem function)

Treatment

• 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.

Outlook (Prognosis)

Acoustic neuromas are benign and noncancerous. They do not spread (metastasize) to other body systems, but they may continue to grow and compress vital structures within the skull.

Possible Complications

• Brain surgery results in complete removal of the tumor in greater than 95% of cases.
• About 95% of patients with small tumors will have no permanent facial paralysis following surgery. However, roughly two-thirds of patients with large tumors will have some permanent facial weakness following surgery.
• Approximately one half of patients with small tumors will retain useful hearing in the affected ear following surgery.
• There may be delayed radiation effects following radiosurgery, including nerve damage, loss of hearing, and facial paralysis.

When to Contact a Medical Professional

Call your health care provider if you experience new or worsening hearing loss or vertigo (dizziness).