Neuroma Akustik

[Melissa Russian]

Anacoustic neuroma, also known as a vestibular schwannoma, is a noncancerous tumor. It develops on the balance nerve, known as the vestibular nerve, and on the auditory nerve, known as the cochlear nerve. These nerves lead from your inner ear to the brain, as shown in the top image. The pressure on the nerve from the tumor may cause hearing loss and imbalance. In some cases, the tumor may grow and affect the cerebellum or other brain tissues, as shown in the magnetic resonance imaging (MRI) scan and illustrations above.

An acoustic neuroma is a noncancerous tumor that develops on the main nerve leading from the inner ear to the brain. This nerve is called the vestibular nerve. Branches of the nerve directly affect balance and hearing. Pressure from an acoustic neuroma can cause hearing loss, ringing in the ear and problems with balance. Another name for an acoustic neuroma is vestibular schwannoma.

An acoustic neuroma develops from the Schwann cells covering the vestibular nerve. An acoustic neuroma is usually slow-growing. Rarely, it may grow quickly and become large enough to press against the brain and affect vital functions.

Symptoms of an acoustic neuroma are often easy to miss and may take years to develop. Symptoms may occur because of the tumor's effects on the hearing and balance nerves. The tumor also can put pressure on nearby nerves controlling facial muscles, known as the facial nerve, and sensation, known as the trigeminal nerve. Blood vessels or brain structures also can be affected by an acoustic neuroma.

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The cause of acoustic neuromas can sometimes be linked to a problem with a gene on chromosome 22. Typically, this gene produces a tumor suppressor protein that helps control the growth of Schwann cells covering the nerves.

Experts don't know what causes this problem with the gene. Often there is no known cause for an acoustic neuroma. This gene change is inherited in people with a rare disorder called neurofibromatosis type 2. People with neurofibromatosis type 2 usually have growth of tumors on the hearing and balance nerves on both sides of the head. These tumors are known as bilateral vestibular schwannomas.

The only confirmed risk factor for acoustic neuromas is having a parent with the rare genetic disorder neurofibromatosis type 2. However, neurofibromatosis type 2 only accounts for about 5% of acoustic neuroma cases.

Neurofibromatosis type 2 is known as an autosomal dominant disorder. This means that the gene related to the disorder can be passed to a child by just one parent. Each child of an affected parent has a 50-50 chance of inheriting it.

Large tumors may press on the brainstem, occasionally preventing the flow of cerebrospinal fluid between the brain and spinal cord. Fluid can build up in your head, a condition known as hydrocephalus. This increases the pressure inside the skull.

Unilateral/asymmetric hearing loss and/or tinnitus and loss of balance/dizziness are early signs of a vestibular schwannoma. Unfortunately, early detection of the tumor is sometimes difficult because the symptoms may be subtle and may not appear in the beginning stages of growth. Also, hearing loss, dizziness, and tinnitus are common symptoms of many middle and inner ear problems (the important point here is that unilateral or asymmetric symptoms are the worrisome ones). Once the symptoms appear, a thorough ear examination and hearing and balance testing (audiogram, electronystagmography, auditory brainstem responses) are essential for proper diagnosis. Magnetic resonance imaging (MRI) scans are critical in the early detection of a vestibular schwannoma and are helpful in determining the location and size of a tumor and in planning its microsurgical removal.

Early diagnosis of a vestibular schwannoma is key to preventing its serious consequences. There are three options for managing a vestibular schwannoma: (1) surgical removal, (2) radiation, and (3) observation. Sometimes, the tumor is surgically removed (excised). The exact type of operation done depends on the size of the tumor and the level of hearing in the affected ear. If the tumor is small, hearing may be saved and accompanying symptoms may improve by removing it to prevent its eventual effect on the hearing nerve. As the tumor grows larger, surgical removal is more complicated because the tumor may have damaged the nerves that control facial movement, hearing, and balance and may also have affected other nerves and structures of the brain.

Unilateral vestibular schwannomas affect only one ear. They account for approximately 8 percent of all tumors inside the skull; approximately one out of every 100,000 individuals per year develops a vestibular schwannoma. Symptoms may develop at any age but usually occur between the ages of 30 and 60 years. Most unilateral vestibular schwannomas are not hereditary and occur sporadically.

Bilateral vestibular schwannomas affect both hearing nerves and are usually associated with a genetic disorder called neurofibromatosis type 2 (NF2). Half of affected individuals have inherited the disorder from an affected parent and half seem to have a mutation for the first time in their family. Each child of an affected parent has a 50 percent chance of inheriting the disorder. Unlike those with a unilateral vestibular schwannoma, individuals with NF2 usually develop symptoms in their teens or early adulthood. In addition, patients with NF2 usually develop multiple brain and spinal cord related tumors. They also can develop tumors of the nerves important for swallowing, speech, eye and facial movement, and facial sensation. Determining the best management of the vestibular schwannomas as well as the additional nerve, brain, and spinal cord tumors is more complicated than deciding how to treat a unilateral vestibular schwannoma. Further research is needed to determine the best treatment for individuals with NF2.

Scientists believe that both unilateral and bilateral vestibular schwannomas form following the loss of the function of a gene on chromosome 22. (A gene is a small section of DNA responsible for a particular characteristic like hair color or skin tone). Scientists believe that this particular gene on chromosome 22 produces a protein that controls the growth of Schwann cells. When this gene malfunctions, Schwann cell growth is uncontrolled, resulting in a tumor. Scientists also think that this gene may help control the growth of other types of tumors. In NF2 patients, the faulty gene on chromosome 22 is inherited. For individuals with unilateral vestibular schwannoma, however, some scientists hypothesize that this gene somehow loses its ability to function properly.

Scientists continue studying the molecular pathways that control normal Schwann cell development to better identify gene mutations that result in vestibular schwannomas. Scientists are working to better understand how the gene works so they can begin to develop new therapies to control the overproduction of Schwann cells in individuals with vestibular schwannoma. Learning more about the way genes help control Schwann cell growth may help prevent other brain tumors. In addition, scientists are developing robotic technology to assist physicians with acoustic neuroma surgery.

Acoustic neuromas are noncancerous, usually slow growing tumors that form along the branches of the eighth cranial nerve (also called the vestibulocochlear nerve). This nerve leads from the brain to the inner ear and branches into divisions that play important roles in both hearing and balance.

Acoustic neuromas arise from Schwann cells, which wrap around and support nerve fibers, hence the name vestibular schwannoma. Schwannomas can occur on any cranial or peripheral nerve in the body, but in the brain, acoustic neuromas are the most common schwannomas.

Many acoustic neuromas do not grow, and though not always, most that do grow tend to do so slowly. They typically do not invade and destroy tissue like cancerous tumors do. However, they can cause symptoms as they grow and push on important surrounding structures.

A growing acoustic neuroma can cause compression of the nerves that enable facial sensation and movement of the facial muscles. With larger tumors, compression of the nerves important for swallowing, speaking and eye movement can occur.

If a growing acoustic neuroma is left untreated, it can cause a dangerous buildup of fluid in the brain or it can compress the cerebellum and brain stem, which can be life threatening. This is rare for patients whose tumors are properly diagnosed and treated.

Hearing loss, dizziness, tinnitus and other symptoms of an acoustic neuroma can be caused by other, more common ear problems, and it is important to consult a doctor for a diagnosis. Because acoustic neuromas often grow on the balance and hearing nerve, the most common symptoms they cause are:

Over 90% of people with acoustic neuromas develop some degree of one-sided (unilateral) hearing loss. People with this type of hearing loss may have difficulty hearing in noisy settings and locating where a sound is coming from. If a person tends to hold a phone to a certain ear or has a hard time following conversation in a crowded room, these may be signs of hearing loss.

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