Acoustic neuroma

Definition

Acoustic neuroma is a noncancerous (benign) tumor that develops adjacent to your brain on a portion of the eighth cranial nerve, which runs from your brain to your inner ear and controls balance and hearing. Also known as vestibular schwannoma, acoustic neuroma is one of the most common types of brain tumors. However, these tumors are rare, occurring in about one person in 100,000.

The signs and symptoms of acoustic neuroma, including hearing loss, develop from the tumor pressing on the hearing portion of the eighth nerve. The tumor also may press on the brainstem. In rare cases, an acoustic neuroma may grow large enough to compress the brainstem and be life-threatening.

Most acoustic neuromas grow slowly, often taking years to become large enough to cause signs and symptoms. Most likely to develop in people between ages 30 and 60, acoustic neuromas are rare in children.

For some people, the tumor remains so small it never causes problems. You may need no treatment other than regular monitoring by your doctor. If you need treatment, you may have options, including radiosurgery and surgical removal.

Symptoms

The signs and symptoms of acoustic neuroma develop from the tumor pressing on cranial nerves.

As the tumor grows, it may be more likely to cause signs and symptoms, although tumor size doesn't always determine effects. It's possible for a small tumor to cause significant signs and symptoms. In many cases, however, a small tumor — less than 1.5 centimeters — may cause no signs or symptoms. Some tumors grow as large as 6 centimeters.

Signs and symptoms may include:

• Hearing loss, usually gradual — although in some cases sudden — and occurring on only one side or more pronounced on one side
• Ringing (tinnitus) in the affected ear
• Dizziness (vertigo)
• Loss of balance
• Facial numbness and tingling

Causes

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Acoustic neuroma

Your eighth cranial (vestibulocochlear) nerve has three branches, which transmit information from your inner ear to your brain. The cochlear branch carries sound. The superior vestibular branch and the inferior vestibular branch carry information regarding balance. Most acoustic neuromas develop on a vestibular branch.

The cause of acoustic neuromas is unknown. There are no known risk factors for developing an acoustic neuroma. However, the tumors, in rare cases, are an indication of neurofibromatosis 2, a genetic disorder that involves the growth of tumors on the vestibulocochlear nerve. Tumors associated with neurofibromatosis often affect the nerve on both sides (bilateral).

Risk factors

The only known risk factor for acoustic neuroma is having the rare genetic disorder neurofibromatosis 2, which involves the development of benign tumors on the vestibulocochlear nerves on both sides of your head, as well as on other nerves.

Neurofibromatosis 2 is known as an autosomal dominant disorder, meaning the mutation occurs on a nonsex chromosome (autosome) and can be passed on from only one parent (dominant gene). If either parent has this disorder, their children have a 50-50 chance of inheriting it.

Some cases of neurofibromatosis 2 develop as a result of a genetic mutation that may occur during fetal development.

When to seek medical advice

See your doctor if you notice hearing loss, particularly in one ear, or develop ringing in your ear, dizziness or have trouble with balance. Early diagnosis of an acoustic neuroma may help keep the tumor from growing large enough to cause serious consequences, such as total hearing loss or a life-threatening buildup of fluid within your skull.

Tests and diagnosis

Because signs and symptoms of acoustic neuroma are likely to develop gradually and because hearing loss, tinnitus and dizziness can be indicators of other middle and inner ear problems, it may be difficult for your doctor to detect the tumor in its early stages. Acoustic neuromas often are found during screening for other conditions.

After asking questions about your symptoms, your doctor will conduct an ear exam and may request the following tests:

• Scans. Magnetic resonance imaging (MRI) or computerized tomography (CT) scans of your head can provide images that confirm the presence of an acoustic neuroma.
• Hearing test (audiometry). During this test conducted by a hearing specialist (audiologist), you wear earphones and hear sounds directed to one ear at a time. The audiologist presents a range of sounds of various tones and asks you to indicate each time you hear the sound. Each tone is repeated at faint levels to find out when you can barely hear. The audiologist also will present various words to determine your hearing ability.
• Electronystagmography (ENG). This test evaluates balance (vestibular) function by detecting abnormal rhythmic eye movement (nystagmus) often present with inner ear conditions. The test measures your involuntary eye movements while stressing your balance in various ways.
• Brainstem auditory evoked response (BAER). This test checks hearing and neurological functions. Electrodes on your scalp and earlobes capture your brain's responses to clicking noises you hear through earphones and record the responses on a graph.

Complications

An acoustic neuroma may cause a variety of complications, including:

• Permanent hearing loss
• Facial numbness and tingling
• Headaches
• Difficulties with balance and clumsy gait
• Mental confusion

Large tumors may press on your brainstem, preventing the normal flow of fluid between your brain and spinal cord (cerebrospinal fluid). In this case, fluid can build up in your head (hydrocephalus), increasing the pressure inside your skull.

Treatments and drugs

There are three options for managing an acoustic neuroma: observation to determine whether it's growing and how fast, radiation and surgical removal.

Monitoring
If you have a small acoustic neuroma that isn't growing or is growing slowly and causes few or no signs or symptoms, you and your doctor may decide to monitor it, especially if you're an older adult or otherwise not a good candidate for treatment.

Your doctor may recommend that you have regular imaging and hearing tests to determine whether the tumor is growing and how quickly. If the scans show the tumor is growing or if the tumor causes progressive hearing loss or other difficulties, you may need to undergo treatment.

Radiation
Several forms of radiation are used to treat acoustic neuromas. One, a procedure called gamma-knife radiosurgery, enables doctors to deliver radiation precisely to a tumor without making an incision. The doctor attaches a lightweight headframe to your numbed scalp. Using imaging scans, your doctor pinpoints the tumor and then plots where to apply the radiation beams. This procedure often is performed under local anesthesia.

The purpose of radiosurgery is to stop the growth of a small tumor. It also may be used for residual tumors, portions of a tumor that traditional brain surgery can't remove without damaging brain tissue.

It may take weeks, months or years before the effects of radiosurgery become evident. Your doctor will monitor your progress with follow-up imaging studies.

Immediate side effects of gamma-knife procedures are minimal and may include nausea, neck stiffness and pain where the frame was attached to your scalp. You may be able to return to normal activity within 24 hours. Long-term risks may include facial paralysis and hearing loss.

Surgical removal
The goal of surgery is to remove the tumor and preserve the facial nerve to prevent facial paralysis and preserve hearing. Performed under general anesthesia, this type of surgery involves removing the tumor through an incision in your skull. You may need to stay in the hospital from four to five days after the surgery, and recovery may take six to 12 weeks.

Risks include infection, bleeding and reactions to the anesthesia. As with radiosurgery, there is a risk of hearing loss and facial paralysis. Even if you experience no further hearing loss after the surgery, you're not likely to regain hearing lost as a result of the acoustic neuroma.

Coping and support

Dealing with the possibility of hearing loss and facial paralysis and deciding which treatment would be best for you can be extremely stressful. Here are suggestions for dealing with your stress:

• Educate yourself about acoustic neuroma. The more you know, the better prepared you'll be to make good choices about treatment. Besides talking to your doctor and your audiologist, you may want to talk to a counselor or medical social worker. Or you may find it helpful to talk to other people with acoustic neuroma.
• Maintain a strong support system. Family and friends can help you tremendously as you go through this difficult time. Sometimes, though, you may find the concern and understanding of other people with acoustic neuroma especially comforting. Your doctor or a medical social worker may be able to put you in touch with a support group. Or you may find a real or virtual support group through the Acoustic Neuroma Association.