Acoustic tumors are non-malignant fibrous growths, originating from the balance or hearing nerve, that do not spread (metastasize) to other parts of the body. They constitute six to ten percent of all brain tumors.
These growths are located deep inside the skull and are adjacent to vital brain centers. The first signs or symptoms one notices usually are related to ear function and include ear noise and disturbances in hearing and balance. As the tumors enlarge, they involve other surrounding nerves having to do with more vital functions. Headache may develop as a result of increased pressure on the brain. If allowed to continue over a long period of time, this pressure on the brain is ultimately fatal.
In most cases these tumors grow slowly over a period of years. In others, the rate of growth is more rapid. In some, the symptoms are mild, and in others, severe, multiple symptoms develop rather rapidly.
The options for management of acoustic neuromas include observation, surgery, and radiation therapy. The management of these tumors depends on patient preference, the age and health of the patient, tumor size and location, as well as the side effects of the tumor (hearing loss, balance, headache, etc.).
Occasionally, physicians will take a “wait and watch” approach to these tumors. This involves serial MRI scans (6 to 12 months) to determine the presence or absence of growth. Many tumors remain quiescent (show no growth) over months to years but most eventually progress. Loss of hearing is a continued risk irrespective of tumor growth. This approach is most often undertaken in patients that are elderly or medically infirmed.
The choice of surgical approach depends upon the size of the tumor and level of residual hearing. It is possible to save hearing in only a minority of cases; if hearing preservation is successful, the preserved hearing is not better than the preoperative level and may be worse. The larger the tumor, the lower the chances for hearing preservation. In some cases with poor preoperative hearing or large tumor, it is better to sacrifice the hearing in order to remove the tumor. All procedures are performed under general anesthesia.
This involves an incision behind the ear. The mastoid and inner ear structures are removed to expose the tumor. The tumor is totally removed. Rarely, only partial removal is accomplished. The mastoid defect is closed with fat taken from the abdomen.
The translabyrinthine approach sacrifices the hearing and balance mechanism of the inner ear. Consequently the ear is made permanently deaf. Although the balance mechanism has been removed on the operated ear, the balance mechanism in the opposite ear usually provides stabilization for the patient in one to four months.
Middle fossa approach
An incision is made above the ear, and the brain is elevated to expose the tumor. The tumor is totally removed in most cases. Every effort is made to preserve the hearing and still remove the tumor. In about 50% of cases, the tumor involves the hearing nerve or the artery leading to the inner ear and total loss of hearing results in the operated ear.
An incision is made behind the ear and the brain is elevated to expose the tumor. The tumor is totally removed in most cases. Every effort is made to preserve the hearing and still remove the tumor. In some cases it is necessary to sacrifice the hearing to achieve tumor removal. In about 50% of cases, the tumor involves the hearing nerve or the artery leading to the inner ear and total loss of hearing results in the operated ear. Following this approach, some patients may experience persistent headaches.
Stereotactic radiosurgery has played an expanding role in the treatment of acoustic tumors. While there are several different ways to be treated with radiosurgery (Gamma Knife, Cyberknife, etc.), all of the treatment options work on the same principle. The goal of radiosurgery is to deliver a very precise, high dose of radiation to the tumor in order to prevent tumor growth. The risk to the facial nerve and the risks of undergoing a craniotomy are reduced with this treatment. In the short term, hearing preservation is attained in the majority of patients with serviceable pre-treatment hearing. However, current treatment methods have only been in use since 1992. The preponderance of the evidence suggests that stereoctactic radiosurgery is a safe and effective treatment of acoustic neuromas. The long-term effects of radiosurgery, including hearing preservation and the effects of radiation delivered in this manner, are not yet known.