An acoustic neuroma is a benign , noncancerous, often slow-growing tumor of the nerve which connects the ear to the brain (8th cranial or auditory) nerve.
Alternative Names
Vestibular schwannoma; Tumor - acoustic; Cerebellopontine angle tumor; Angle tumor
Causes, incidence, and risk factors
These tumors are thought to arise when there is a defect in a certain tumor suppressor gene, which normally prevents tumors from occurring. The cause of the genetic defect is not known. However, acoustic neuroma is often linked with the genetic disorder neurofibromatosis type 2 ( NF2 ). Acoustic neuromas are relatively uncommon in general, but they are one of the most common types of brain tumors. They affect approximately 1 out of 100,000 people per year. The tumor is most commonly located at the base of the brain, where the auditory nerve leaves the skull cavity and enters the bony structure of the inner ear.
Signs and tests
The health care provider may diagnose an acoustic neuroma based on the history, neurological examination or testing of the patient. The results of a physical examination are often unremarkable, except for the following signs:
facial drooping on one side unsteady walkdrooling If the tumor is large, there may additionally be signs of increased pressure on the brain ( increased intracranial pressure ), including the following:
nausea and vomiting unilateral (one side only) dilated pupil -- see eyes, pupils different size
lethargy (sleepiness) The most useful (i.e., sensitive and specific) test to identify acoustic neuromas is an MRI of the head . Other useful tests used to diagnose acoustic neuroma and to differentiate it from other causes of dizziness or vertigo include:
head CTaudiology (a test for hearing) caloric stimulation (a test for vertigo) electronystagmography (a test of equilibrium and balance) brainstem auditory evoked response (BAER, a test of hearing and brainstem function)
Treatment
Surgery
Goals of surgical treatment are removal of the tumor and prevention of facial paralysis. Preservation of hearing is more difficult. If a tumor is removed when it is very small, hearing may be preserved. Any hearing that is lost prior to surgery will not be regained. Large tumors usually result in total loss of hearing on the affected side.
Large tumors may also compress nerves important for facial movement and sensation. These tumors can typically be safely removed, but the surgery often results in paralysis of some facial muscles.
Extremely large tumors may additionally compress the brainstem, threatening other cranial nerves and preventing the normal flow of cerebrospinal fluid . This can lead to a build-up of fluid in the head ( hydrocephalus ) which can cause potentially life-threatening increased intracranial pressure . Goals of surgery in these cases are treatment of the hydrocephalus and decompression of the brainstem.
Stereotactic radiosurgery
The goal of radiation therapy is to slow or stop the tumor growth, not to cure or remove the tumor. Radiosurgery is often performed in elderly or sick patients who are unable to tolerate brain surgery. Sometimes during brain surgery to treat acoustic neuromas, not all of the tumor can be safely removed, and some residual tumor must be left behind. Radiosurgery is often used post-operatively to treat residual tumor in these cases. Radiosurgery is only appropriate for small tumors, so that radiation damage to surrounding tissues can be minimized. Like brain surgery, radiosurgery can sometimes result in facial paralysis or loss of hearing. Observation
Since these tumors usually grow very slowly, small tumors that have minimal or no symptoms (asymptomatic) can be safely observed with regular MRI scans and left untreated unless they grow dangerously. Very often elderly patients will die of other natural causes before small, slow growing tumors become symptomatic.
Expectations (prognosis)
Acoustic neuromas are benign and noncancerous. They do not spread (metastasize) to other body systems, but they may continue to grow and compress vital structures within the skull.
Calling your health care provider
Call your health care provider if you experience new or worsening hearing loss or vertigo (dizziness).