ADAM Health Encyclopedia

Acoustic neuroma

Definition

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

Alternative Names

Causes

These tumors are thought to occur when there is a defect in a gene that normally prevents tumors from forming. 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.

The tumor is usually found at the base of the brain.

Symptoms

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

Common symptoms include:

• Abnormal sensation of movement (vertigo)
• Hearing loss in the affected ear
• Ringing (tinnitus) in the affected ear

Less common symptoms include:

• Difficulty understanding speech
• Dizziness
• Headache
  • Upon waking up in the morning
  • Wakes you from sleep
  • Worse when lying down
  • Worse when standing up
  • Worse when coughing, sneezing, straining, or lifting (Valsalva maneuver)
  • With nausea or vomiting
• Loss of balance
• Numbness in the face or one ear
• Pain in the face or one ear
• Vision abnormalities that are temporary
• Weakness of the face

Exams and Tests

The health care provider may diagnose an acoustic neuroma based on your medical history, an examination of your nervous system, or tests. A physical examination may show the following signs:

• Drooling
• Facial drooping on one side
• Unsteady walk

If the tumor is large, there may also be signs of increased pressure on the brain (increased intracranial pressure), including the following:

• Dilated pupil on one side only (see eyes, pupils different size)
• Nausea and vomiting
• Sleepiness

The most useful test to identify acoustic neuromas is an MRI of the head. Other useful tests used to diagnose acoustic neuroma and to tell it apart from other causes of dizziness or vertigo include:

• Head CT
• Hearing test (audiology)
• Test of equilibrium and balance (electronystagmography)
• Test of hearing and brainstem function (brainstem auditory evoked response)
• Test for vertigo (caloric stimulation)

Treatment

• Surgery
  • Goals of surgery are to remove the tumor and prevent paralysis of the face. Preserving hearing is more difficult. If a tumor is removed when it is very small, hearing may be preserved. You cannot get back any hearing that is lost before surgery. Large tumors usually result in total loss of hearing on the affected side.
  • Large tumors may also press down on nerves important for movement and feeling in the face. These tumors can typically be safely removed, but the surgery often leads to paralysis of some muscles of the face.
  • Extremely large tumors may also press on the brainstem, threatening other nerves and preventing the normal flow of cerebrospinal fluid. This can lead to a build-up of fluid (hydrocephalus), which can increase pressure in the head and can be life-threatening. Goals of surgery in these cases are to treat the hydrocephalus and relieve pressure on 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 of the tumor must be left behind. Radiosurgery is often used after surgery in these cases to treat the tumor that remains.
  • 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 paralysis of the face or loss of hearing.
• Observation
  • Since these tumors usually grow very slowly, small tumors that have few or no symptoms can be safely watched 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 show symptoms.

Outlook (Prognosis)

Acoustic neuromas are not cancer. They do not spread (metastasize) to other body systems, but they may continue to grow and press down on important structures in the skull.

Possible Complications

• Brain surgery can completely remove the tumor in most cases.
• Most people with small tumors will have no permanent paralysis of the face after surgery. However, about two-thirds of patients with large tumors will have some permanent facial weakness after surgery.
• Approximately one-half of patients with small tumors will get back useful hearing in the affected ear after surgery.
• There may be delayed radiation effects after radiosurgery, including nerve damage, loss of hearing, and paralysis of the face.

When to Contact a Medical Professional

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

Abram S, Rosenblatt P, Holcomb S. Stereotactic radiation techniques in the treatment of acoustic schwannomas. Otolaryngol Clin North Am. 2007;40:571-588.

Bennett M, Haynes DS. Surgical approaches and complications in the removal of vestibular schwannomas. Otolaryngol Clin North Am. 2007;40:589-609.

Backous DD, Pham HT. Guiding patients through the choices for treating vestibular schwannomas: balancing options and ensuring informed consent. Otolaryngol Clin North Am. 2007;40:521-540.