Acoustic neuroma, also referred to as vestibular schwannoma or neurilemmoma, is a rare, benign tumor found on the vestibulocochlear nerve, the eighth cranial nerve in the head. It accounts for 6 percent of all brain tumors, and doctors make approximately 2,000 to 3,000 diagnoses each year in the United States, according to AcousticNeuroma.org.
Causes
The exact cause of acoustic neuroma is unknown, but the tumor arises from the nerve covering cells, called Schwann cells, of the vestibulocochlear nerve. The vestibulocochlear nerve runs from the brain to the inner ear and functions as a sensory nerve. It transmits information about hearing and balance. As the tumor grows, it presses on the nerve, causing disturbances in hearing and balance.
Symptoms
Symptoms of acoustic neuroma depend on the size and location of the tumor, as it is not until the tumor presses on the nerves and other brain structures that symptoms develop. Generally, the first noticeable symptom is impaired hearing or hearing loss in one ear. Other symptoms of vestibulocochlear nerve compression include ringing in the ears, dizziness and loss of balance. If the tumor presses on another cranial nerve, called the trigeminal nerve, facial numbness and weakness occur. If the tumor grows large enough it may damage nearby brain structures.
Complications
Damage from acoustic neuroma may result in permanent hearing loss along with balance difficulties and clumsy walking. This is due to irreversible damage to the vestibulocochlear nerve. Disruption of vital functions, such as breathing, heart rate and blood pressure, may occur if the tumor grows large enough to press on the brain stem. A tumor also may disrupt the flow of cerebrospinal fluid (CSF) in the brain resulting in fluid buildup, a condition called hydrocephalus, which leads to increased pressure in the skull. Seek medical attention immediately if hydrocephalus is present.
Diagnosis
Diagnosis of acoustic neuroma begins with a complete medical history and analysis of symptoms. Diagnosis often is difficult in early stages due to the lack of symptoms or the similarities in symptoms to other inner and middle ear conditions. However, if acoustic neuroma is suspected, doctors can order several types of medical tests to confirm diagnosis. MRI and CT scans provide detailed images of the head to locate abnormal growths. Hearing tests assess the extent of hearing damage. An electronystagmography tests balance function by looking for abnormal eye movements. A BAER, or brainstem auditory evoked response, test determines how sound information is passed along the vestibulocochlear nerve by placing electrodes on the scalp to measure the brain's response to clicking noises.
Treatment
Monitoring, radiosurgery and surgical removal of the tumor are three treatment options for acoustic neuroma. Physicians generally reserve monitoring for small and very slow-growing tumors that produce no or very few symptoms or for individuals who are unable to safely undergo surgery. Monitoring involves frequent imaging and hearing tests to detect if the tumor has grown enough that other treatment options should be considered. Stereotactic radiosurgery uses precisely aimed beams of radiation to stop tumor growth. Complete tumor removal without disruptions in neurological function is the primary goal in surgical excision or removal.
