What is an Acoustic Neuroma?
An acoustic neuroma, also called vestibular schwannoma is a benign tumor that originates on the balance/hearing nerve that passes from the inner ear to the brain. In most cases, these one-sided tumors grow slowly over a number of years. They do not spread to other parts of the body. Although nonmalignant, they can do harm or even become life-threatening as they enlarge and begin to press on nerves and vital structures. Usually the diagnosis for patients is made between the ages of 30 and 60. More women than men are likely to experience an acoustic neuroma. Acoustic neuromas are actually quite rare, accounting for less than 5% of all primary brain tumors, and their exact cause is unknown. The even more rare bilateral type of acoustic neuroma, Neurofibromatosis Type II, tends to develop in patients at a younger age and is an inherited genetic condition.
The Incidence of Acoustic Neuroma
The incidence of acoustic neuroma (AN) has usually been estimated at 10 per million of population (1/100,000) per year. For Denmark, a country of 5.2 million that keeps excellent records, a most recent study at the Gentofte University Hospital in Copenhagen showed a realistic incidence of acoustic neuroma of 13 per million of population. It seems safe to estimate that for New Jersey, with a population of more than 8 million, there are about 80-90 new cases of AN each year.
Tumor Growth Rates
Tumor growth rates are highly variable. Periods of no growth are likely. There can also be periods of rapid growth. Perhaps 10-15% are fast growing at a rate of more than 1.0 cm/year. But for the most part, ANs are slow growing at the rate of about 1.0-2.0 mm/year. One 1995 study of 123 patients showed a mean growth rate of 3.2 mm/year, while another study in 1997 for 48 elderly patients showed a mean growth rate of 2.9 mm/year, with the lowest rates for tumors confined to the internal auditory canal. There appears to be no difference in growth rates between older and younger individuals.
Tumor Sizes (diameter)
A scale commonly used to describe tumor size is:
Small, <1.0 cm
Medium, 1.0 - 2.5 cm
Large, 2.5 - 4.0 cm
Giant, >4.0 cm
(2.54 cm equals one inch)
Treatment Options for Acoustic Neuroma
If an acoustic neuroma is small and acute symptoms are not present, a first option is to “wait-and-watch” by monitoring the growth characteristics of the tumor with periodic MRIs (Magnetic Resonance Imaging). Careful monitoring can determine if or when intervention may be necessary. Any rapid growth especially needs to be watched closely to avoid the complications associated with the treatment of large tumors. Surgical removal of the tumor is a second option. Advances in microsurgical techniques in recent years have greatly reduced the risk of damaging nerve tissue. In some cases, partial removal may be indicated to avoid serious complications. The best surgical outcomes are from medical centers with experienced acoustic neuroma teams. Thirdly, radiosurgery and radiotherapy (Gamma Knife or Linac) are options that have become increasingly attractive because they are non-invasive procedures with few if any complications. Radiosurgery treats the tumor with high dose radiation in a one-day session, whereas radiotherapy involves multiple sessions in which the total dose is spread over several days or weeks. Tumor growth control, meaning shrinkage or unchanged size of the tumor, has been achieved in 95-98% of cases. Individual treatment is best decided by the informed patient and medical professionals who specialize in treating acoustic neuromas. (More detailed information)