Acoustic Neuroma

Definition

Although it's frightening to learn that you have a tumor growing inside your head, it may be somewhat comforting to know that an acoustic neuroma is noncancerous (benign) and usually slow growing. These tumors develop adjacent to your brain on a portion of the eighth cranial nerve, which runs from your brain to your inner ear. Also known as vestibular schwannoma, acoustic neuroma is one of the most common types of brain tumors.

Symptoms of acoustic neuroma, including hearing loss, develop from the tumor pressing on the nerve. But, acoustic neuromas don't invade brain tissue like cancer does.

For some people, an acoustic neuroma remains so small it never causes problems. Treatment options include regular monitoring, radiation and surgical removal.

Symptoms

The signs and symptoms of acoustic neuroma develop from a 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 of less than about six-tenths of an inch — about 1.5 centimeters (cm) — may cause no signs or symptoms. Some tumors grow as large as about 2.5 inches (more than 6 cm).

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 weakness

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.

When to see your doctor
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.

Causes

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. 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.

Acoustic neuromas are most common in people between the ages of 30 and 60 years old.

Some evidence has suggested that persistent exposure to very loud noise or heavy cell phone use may play a role in the development of acoustic neuroma, but findings from studies looking into these associations have been inconclusive.

Complications

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

• Permanent hearing loss
• Facial numbness and weakness
• Difficulties with balance and clumsy gait

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.

Preparing for your appointment

You're likely to start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to an ear, nose and throat specialist (otolaryngologist), a neurologist, a neurosurgeon or an otolaryngologist that specializes in neurological surgeries (neurotologist).

Because there's often a lot of ground to cover during your appointment, it's a good idea to be well prepared. Here's some information to help you get ready for your appointment, and what to expect from your doctor.

What you can do

• Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
• Write down key personal information, including any major stresses or recent life changes.
• Make a list of all medications, as well as any vitamins or supplements, that you're taking.
• Ask a family member or friend to join you, if possible. Sometimes it can be difficult to soak up all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

Preparing a list of questions will help you make the most of your time with your doctor. For acoustic neuroma, some basic questions to ask your doctor include:

• What is likely causing my symptoms?
• Are there any other possible causes for my symptoms?
• What kinds of tests do I need?
• What treatment options are available?
• Which one do you recommend for me?
• What is the likelihood of side effects from each treatment option?
• What happens if I do nothing?
• Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first begin experiencing symptoms?
• Have your symptoms been continuous, or occasional?
• How severe are your symptoms?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?

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 will also 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.

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.

Stereotactic radiosurgery
Stereotactic radiosurgery, such as 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 tumor. It may also 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 and hearing tests.

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 six days after the surgery, and recovery may take six weeks or more.