What is an acoustic neuroma?
An acoustic neuroma (sometimes termed neurinoma or schwannoma) is a benign (non-cancerous) tumor that arises on the nerve of hearing and balance (8th Cranial Nerve) within the inner ear. The nerve of hearing and balance sends information from the ear to the brain.
What causes an acoustic neuroma?
The cause of most acoustic neuromas is unknown. There is a small group of patients who have a genetically inherited form of acoustic neuroma called neurofibromatosis type 2.
How fast does an acoustic neuroma grow?
An acoustic neuroma is usually very slow growing. When small an acoustic neuroma will remain within the inner ear. However, as the tumor grows it extends out of the inner ear and can push up against the brain.
How often do acoustic neuromas occur?
Acoustic neuromas have been found during autopsy in 2.4% of the general population. Estimates of symptomatic acoustic neuromas range from one in every 3,500 persons to five in every million people. More women than men are affected, and most acoustic neuromas are diagnosed between the ages of thirty and sixty.
What are the symptoms of an acoustic neuroma?
Although the acoustic neuroma usually arises on the balance portion of the nerve of hearing and balance, the first symptoms are usually hearing related. The most common symptom of an acoustic neuroma is hearing loss in one ear, the ear with the acoustic neuroma. This hearing loss may be mild but is usually progressive. One percent of patients with an acoustic neuroma will have a sudden, severe hearing loss. Other symptoms include a noise (tinnitus) in the ear with the tumor or a sense of ear fullness in that ear. Many patients complain of vague imbalance, occasionally vertigo (the false sensation of moving). When an acoustic neuroma is large and pushes against the brain it can cause headache, facial numbness and facial weakness.
How do you identify the tumor?
The first step in the diagnosis of an acoustic neuroma is a hearing test. If a hearing test shows a one sided hearing loss, or an asymmetric hearing loss (worse in one ear than the other), then the index of suspicion for an acoustic neuroma is high. If there is tinnitus in one ear, even if the hearing test is normal, there is a high index of suspicion for an acoustic neuroma. The definitive diagnostic test for an acoustic neuroma is Magnetic Resonance Imaging (MRI) of the nerve of hearing and balance. This test is usually performed with injection of a contrast material, called gadolinium. With contrast the MRI is 100% effective in diagnosing even the smallest acoustic tumor. Without contrast, small tumors, limited to the inner ear, may be missed. Some people can not have an MRI scan, for various reasons. In that instance a CT scan can be performed. Although not as accurate as an MRI, it will diagnose most acoustic tumors.
What is the treatment of acoustic neuroma?
Treatment of an acoustic neuroma depends upon the size of the tumor, the rate of growth of the tumor, the location of the tumor, the amount of hearing loss and the age of the patient. These factors are often inter-related and must be considered in the context of each individual patient. There are three approaches to treatment: expectant observation (no treatment), surgical removal and focused radiation therapy (radiosurgery).
Because of the sensitivity of MRI scanning acoustic neuromas are now often diagnosed when they are very small. Accordingly, one choice is to just observe the tumor for growth. Often, after many years, the tumor does not grow. The tumor can be monitored with repeat MRI scans, which are very safe because they involve NO radiation exposure. If a patient chooses to monitor the tumor, the MRI is repeated after six months, then yearly. The main risk of this conservative approach is that hearing will likely be lost during the observation period, even if the tumor does not grow.
If the tumor is growing, or if the patient has a very strong desire to preserve hearing, then surgical excision or radiation therapy are options. Surgery is the only truly curative option, because the tumor can potentially be completely removed. Surgery is generally suggested for younger patients, under the age of 65 years. Radiation therapy is suggested for patients over the age of 65 years. Radiation therapy stops tumor growth in 95% of cases. It does not cure the tumor. The reason that radiation therapy is not suggested for younger patients is that there is a very small potential for malignant transformation from a benign acoustic neuroma to a cancerous acoustic neuroma, over time, usually at least 15 years after radiation. In addition, if the tumor continues to grow (5%), it is more difficult to surgically remove after radiation treatment. Radiation therapy is otherwise of very low risk, is done in one treatment and involves a one night hospital stay. Residual hearing can be preserved in 50-60% of patients undergoing radiation therapy.
There are several different surgical approaches to removing an acoustic neuroma, depending upon the size of the tumor and hearing. The surgery is usually done by a team, including an ear surgeon (Otologist) and a neurosurgeon. If there is good hearing and the tumor is small, the surgical approach is above the ear (middle cranial fossa). If the tumor is medium sized with good hearing, the approach is behind the ear (posterior fossa). If there is no useful hearing the approach is through the ear (translabyrinthine).