Acoustic neuroma

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on September 12, 2022.

An acoustic neuroma—also called a vestibular schwannoma—is a brain tumor, but it isn’t cancer. Unlike a cancerous tumor, acoustic neuromas don’t spread to other parts of the body or brain. However, as an acoustic neuroma grows, it presses upon essential parts of the brain that play a role in hearing and balance.

According to the Acoustic Neuroma Association, these tumors are rare and account for 6 to 10 percent of all brain tumors. In the United States, about 2,500 to 3,000 people are diagnosed with acoustic neuromas every year—or one in every 100,000 people. These tumors tend to occur in people between the ages of 30 and 60, although they may affect people of all ages.

Acoustic neuromas grow in cells surrounding the vestibulocochlear nerve, which connects the ear and the brain and helps control hearing and balance. These cells are called Schwann cells, and they form a protective layer around nerves. An acoustic neuroma may develop when there’s an overproduction of Schwann cells around this nerve.

Acoustic neuromas tend to be slow-growing, developing over many years without causing any problems. However, some of these tumors grow faster and cause more severe symptoms.

Symptoms of acoustic neuroma

The most common symptoms associated with acoustic neuromas are:

Hearing loss (on one side). About 90 percent of patients experience one-sided hearing loss, in the ear affected by the tumor, as their initial symptom, according to the National Organization of Rare Diseases.

Ringing in the ears. This is known as tinnitus.

Dizziness. In rare cases, patients experience dizziness or vertigo before hearing loss.

Balance problems. Patients with acoustic neuromas may feel unsteady or have trouble with balance. Since these tumors tend to be slow-growing, the body can adjust to it so this symptom may be less noticeable.

More severe symptoms that tend to appear later, as the tumor grows larger, may include:

Numbness, paralysis or pain in the face. Numbness or paralysis may be caused by the acoustic neuroma. As it grows larger, the tumor may press against nearby cranial nerves, causing lack of feeling or muscle control.

Headaches. In rare cases, headaches may be the first sign of an acoustic neuroma. Headaches may also be the result of fluid buildup or pressure from the growing tumor.

Clumsiness. Acoustic neuromas may impair the body’s ability to coordinate voluntary movements.

Confusion. Mental confusion also may occur when fluid accumulates in the skull causing pressure on brain tissues.

Over time, if an acoustic neuroma grows large enough and starts putting pressure on the brain, it may become life-threatening. However, most cases are discovered and treated before they get to this point.

The acoustic neuroma diagnosis process

The symptoms of acoustic neuroma can be similar to those of ear infections or other ear problems. Health professionals use a variety of tests and diagnostic tools to diagnose acoustic neuromas.

Various exams, hearing tests (also known as audiometry) and imaging tests are all used to discover and diagnose an acoustic neuroma. These tests may include:

Audiogram. This is usually the first step in testing for acoustic neuroma. An audiogram uses earphones to measure the patient’s response to sounds and speech, looking for increased pure tone average, which is a measure of hearing impairment, or high-frequency hearing loss. This test also looks for increased speech reception threshold (SRT), the lowest hearing level at which someone recognizes at least half of speech material. It may also identify decreased speech discrimination (SD), or the inability to understand speech, rather than the inability to hear—which is a symptom of high-frequency hearing loss.

Brainstem auditory evoked response (BAER) test. A BAER is a hearing test that measures brain wave activity in response to clicks or tones and may reveal issues with hearing and neurological function. Electrodes attached to each earlobe record the brain’s response to these sounds.

Electronystagmography test. This test is used to evaluate balance and look for abnormal involuntary eye movements, a condition known as nystagmus, often caused by inner ear complications.

Imaging tests used to detect acoustic neuroma include:

Magnetic resonance imaging (MRI) scans. These produce detailed images of the area and reveal the size and location of the tumor. MRI with contrast dye is widely considered the most sensitive test when looking for acoustic neuromas. Thanks to the expanded use of MRIs, many neuromas may be found when they’re still small and haven’t caused any hearing loss.

Computerized tomography (CT) scans. These machines capture images showing cross-sections of the structures in the brain. CT scans are sometimes used to determine the size and location of the tumor. But a CT doesn’t directly show an acoustic neuroma. Instead, it may show that the bony ear canal is wider than normal, which may be a sign of an acoustic neuroma.

Causes of acoustic neuroma

Acoustic neuromas are thought to be caused by a faulty gene on chromosome 22. This gene is supposed to regulate the production of Schwann cells, but in people with an acoustic neuroma, this gene doesn’t work properly. So Schwann cells grow out of control, forming a tumor.

Most acoustic neuromas aren’t caused by inherited genetic changes, meaning that the gene malfunction seems to arise randomly most of the time.

However, people with tumors that affect hearing in both ears often have an inherited condition called neurofibromatosis type 2 (NF2). Tumors on both nerves are called bilateral vestibular schwannomas, or bilateral acoustic neuromas, while a tumor affecting hearing on one side is referred to as unilateral.

NF2 causes affected individuals to inherit the faulty gene on chromosome 22 that is thought to be responsible for acoustic neuromas. Those who have this condition and go on to develop tumors on their hearing nerves usually experience symptoms earlier than others, when they are teenagers or young adults.

Treatment of acoustic neuroma

The three main treatment options for acoustic neuromas are:

An appropriate treatment option depends on:

  • Size of the tumor
  • Severity of symptoms/hearing loss
  • Age and overall health
  • Personal preferences

Observation: Observation (or watchful waiting) is a treatment approach that doctors may recommend for small, slow-growing tumors. In this case, patients may undergo regular MRI scans to monitor the tumor and make sure it isn’t growing. If the tumor starts to cause problems, treatment options are reassessed. A specialist experienced in brain tumors should monitor the neuroma to determine  whether other treatment options should be considered.

Surgical removal: Some acoustic neuromas need to be surgically removed. This procedure may be complicated or relatively simple, depending on the tumor size and severity of hearing loss.

The three most common surgical approaches are:

Translabyrinthine approach. The surgeon accesses the tumor behind the ear and opens the mastoid bone and some of the inner ear, then removes all or as much of the tumor as possible without harming nearby structures before removing a portion of the inner ear. This approach may be used when the tumor is large and has caused significant hearing loss or when it’s impossible to restore hearing loss.

Retrosigmoid approach. After accessing the occipital bone, the surgeon removes the bone over the internal auditory canal to excise the tumor. Some portions of the tumor may be left if removal would damage nerves or brain tissue. This approach is most often used when tumors are smaller and are located in the auditory canal, but a size tumor of any size may be removed with this approach.

Middle fossa approach. The surgeon cuts above the ear in the lateral skull bone to view the internal auditory canal and remove the tumor, then fat from elsewhere in the body is used to help close the opening. This approach typically works well in preserving hearing and is meant for smaller tumors that remain in the internal auditory canal.

Surgery to remove a small tumor may stop the progression of hearing loss and relieve other symptoms. However, removing a larger tumor may not result in the same improvements, as the tumor may have already caused significant nerve damage. The surgery itself may also damage the nerves, potentially worsening symptoms.

Radiation therapy: Radiation therapy may shrink the tumor or slow its growth. Acoustic neuromas may be treated with a type of radiation therapy called radiosurgery, which sends a beam of radiation toward the tumor to destroy tumor cells and prevent them from growing.

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