Acoustic Neuroma Overview

An acoustic neuroma, also known as vestibular schwannoma, is a brain tumor. This non-cancerous tumor is located on the eighth cranial nerve, called the vestibular nerve, which connects the inner ear to the brain. This growth is quite rare and accounts for approximately seven percent of all brain tumors. About 2,500 cases of acoustic neuromas are diagnosed each year. It typically occurs on one side of the head and does not spread to other parts of the body. Although benign, if left untreated, acoustic neuromas can cause severe neurological damage.

What Causes Acoustic Neuroma?

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The exact cause of an acoustic neuroma is unknown, but several environmental factors are being investigated. Exposure to loud noises and radiation around the head has been related to the development of an acoustic neuroma. Although no connection between cell phone usage and this kind of brain tumor has been made, many experts recommend the use of hands-free devices until more research is completed. Genetics may play a small role in the etiology of acoustic neuroma, as a hereditary condition called neurofibromatosis type 2 can lead to its development. This has been only observed in about five percent of the cases.

Neurofibromatosis Type 2

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Neurofibromatosis type 2 is a genetic disorder that causes noncancerous tumors to grow in an individual's nervous system. Acoustic neuromas are the most commonly occurring tumors associated with this condition. The growths form along the auditory nerve, which connects the brain to the inner ear. In addition to acoustic neuromas, other types of tumors may also form along other nerves. The symptoms tend to appear for the first time when an individual is in their teens or early twenties, though there have been cases that begin earlier or later. Most individuals develop acoustic neuromas in both ears by the time they're thirty years old. The other potential tumors vary. The complications depend on where the tumors form and how large they are.

What Are The Symptoms Of Acoustic Neuroma?

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The vestibular nerves transmit sound information to the brain and plays a role in balance. As it grows, acoustic neuromas can negatively impact these two functions. Initial signs of one of these tumors include one-sided hearing loss, tinnitus (ringing in the ear), and dizziness. Vertigo, which is a consistent loss of balance, can also result. If an acoustic neuroma becomes too large, it can place pressure on the brain stem, brain tissue, and other cranial nerves which can lead to neurological problems including impaired facial sensation and whole body function.

Diagnosing Acoustic Neuroma

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Along with an ear exam and hearing test, a computerized tomography (CT) scan or magnetic resonance imaging (MRI) procedure are needed to diagnose acoustic neuromas. The auditory brainstem response test is another diagnostic tool that evaluates the transmission of information from the inner ear to the brain. This test can be used to diagnose an acoustic neuroma before hearing loss is observed. Since the initial signs are mild and this kind of tumor is slow-growing, it often is not diagnosed early. It is important to obtain regular ear exams as well as discuss any hearing loss with an audiologist.

Treatment Options For Acoustic Neuroma

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Treatment for an acoustic neuroma depends on the size and location of the tumor when it is initially diagnosed. When it is a small tumor, the typical treatment is regular observation. When an acoustic neuroma is a moderate to large size, the treatment may consist of surgical removal or radiation. If the tumor growth has affected the function of the nerves, surgical removal may cause permanent damage to these nerves, making radiation the preferable method. A new surgical technique, radiosurgery with a gamma knife, is being applied to slow the growth and reduce the size of acoustic neuromas.

Tinnitus

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Tinnitus, which refers to the repetitive or constant ringing in the ears, is a common complication of an acoustic neuroma. Rarer types of tinnitus may take the form of buzzing or pulsing instead of ringing. The ringing sound is typically only present in the affected ear, though individuals may experience ringing in both ears if both auditory nerves have acoustic neuromas. While acoustic neuroma is a rare phenomenon, about fifteen to twenty percent of affected individuals also experience tinnitus. Rather than being its own condition, tinnitus is considered a symptom of an underlying issue. If individuals notice one or both ears are ringing, especially if this is combined with hearing loss, they should talk to a doctor.

Balance Difficulties

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The inner ear is responsible for regulating an individual's balance. When an acoustic neuroma damages the inner ear or the messages between the inner ear and the brain, it leads to balance difficulties. Affected individuals may lose their balance or feel unsteady when they walk. Balance difficulties can take a variety of forms. Some individuals feel like they're moving or that the world is moving around them, even when it isn't. 

Others feel lightheaded or faint, like they're experiencing a blood pressure drop. Patients might feel unsteady and have trouble with a straight, balanced gait. General dizziness, a sensation of floating, and blurred vision are also associated with inner ear issues. The specific type of balance problem an individual is having can help their doctor determine the underlying cause.

Hearing Loss

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Hearing loss is the most common complication of an acoustic neuroma. In most cases, the hearing loss will be gradual, and patients may not notice it at first. The loss also tends to occur only on the affected side. However, if individuals have acoustic neuromas on both nerves, they may experience gradual hearing loss in both ears. Rather than being balanced, hearing loss will typically be more pronounced in one ear. Some patients do experience sudden hearing loss, which can be confusing and alarming. If individuals notice they're losing hearing in one or both ears, they should see their doctor to ascertain the cause. Most causes of hearing loss can be treated.

Facial Weakness And Numbness

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The hallmark symptoms and complications of acoustic neuroma are tinnitus, balance problems, and hearing loss, though there have been rare cases where individuals experience facial numbness. Even more rarely, people might experience loss of muscle movement or weakness in their facial muscles. This weakness can lead to partial or total paralysis of certain facial muscles. Facial weakness occurs when the acoustic neuroma is large enough or positioned just enough to inhibit the facial nerve. If there's increased pressure against this nerve, patients might also experience unexpected tear formation and dry eyes because the facial nerve regulates tear production. Numbness occurs when the tumor becomes large enough that it affects the sensory nerves in the face, leading to a loss of sensation.