DEAR MAYO CLINIC: I was diagnosed with an acoustic neuroma last year. My doctor says I likely won't need treatment. But I know others who have had the same condition and had surgery to remove the tumor. Why would I not need any treatment?
ANSWER: An acoustic neuroma, more accurately called a vestibular schwannoma, is a benign tumor that grows on the balance and hearing nerves. These nerves twine together to form the vestibulocochlear nerve, which runs from your inner ear to your brain. Hearing loss due to an acoustic neuroma often occurs predominantly on one side only. For many years, doctors thought surgical removal was the best treatment. Then, in the mid-1980s, stereotactic radiosurgery, such as Gamma knife radiosurgery, was shown to be safe and effective. Increasingly, doctors are concluding that, in some cases, no treatment may be just as good as or better than active intervention in the long run.
An acoustic neuroma arises from the cells (Schwann cells) that make up the insulation surrounding the vestibulocochlear nerve. What causes these cells to overgrow and form a tumor isn’t certain, but it may be related to sporadic genetic defects. Acoustic neuromas are uncommon and usually are diagnosed between ages 30 and 60. In rare cases, the overgrowth may be caused by an inherited disorder, called neurofibromatosis type 2.
Most acoustic neuromas grow very slowly, although the growth rate is different for each person and may vary from year to year. Some acoustic neuromas stop growing, and a few even spontaneously get smaller. The tumor doesn’t invade the brain but may push against it as it enlarges.
Signs and symptoms typically include loss of hearing in one ear, ringing in the ear (tinnitus) and unsteadiness while walking. Occasionally, facial numbness or tingling may occur. Rarely, large tumors may press on your brainstem, threatening vital functions. A tumor can prevent the normal flow of fluid between your brain and spinal cord so that fluid builds up in your head — a condition caused hydrocephalus.
Diagnosis can be a challenge because early signs and symptoms may be attributed to more familiar causes, such as aging or noise exposure. If an acoustic neuroma is suspected, such as when a hearing test reveals loss predominantly in one ear, the next step is to undergo imaging — typically an MRI — to look for evidence of a tumor on the vestibulocochlear nerve. Increasingly, acoustic neuromas are being discovered as incidental findings when people undergo an MRI scan for unrelated reasons, such as chronic headache, multiple sclerosis or even during surveillance imaging for another unrelated tumor.
Treatment varies depending on the size and growth of the acoustic neuroma, symptoms, and your personal preferences. Options include:
Research is ongoing to compare the three treatment strategies. But, based on long-term data, there appears to be surprisingly little difference in outcome no matter which treatment is chosen for smaller tumors. Talk to your doctor to make sure you are being monitored appropriately for your situation. (adapted from Mayo Clinic Health Letter) — Dr. Michael Link, Neurologic Surgery, Mayo Clinic, Rochester, Minnesota