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.

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.

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

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), including the following:

• 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)