The Merck Manual defines acoustic neuroma as a noncancerous tumor that originates in the cells that wrap around the auditory nerve. It is also known by the names vestibular schwannoma, acoustic schwannoma, acoustic neurilemmoma, and acoustic neurinoma. Acoustic neuroma is one of the most common types of brain tumor. Incidence of acoustic neuroma is relatively low, affecting approximately one in 100,000 people. It is slow-growing and may cause no symptoms, or it may lead to hearing loss and other inner ear-related problems.
Pathophysiology
Cranial nerves originate from the brain and are responsible for a variety of functions. The nerves are wrapped by a sheath of Schwann cells. An acoustic neuroma is a benign growth on the sheath of the eighth cranial nerve, the vestibulocochlear nerve. Although acoustic neuromas are classified as a brain tumors, the growth does not actually invade the brain; it may exert pressure on the brain and nerve tissue as it enlarges. Because of its location in the inner ear, it may cause symptoms associated with hearing and balance.
Symptoms
The most common symptom of acoustic neuroma is one-sided hearing loss. Other common symptoms include ringing the ear, sensation of fullness in the ear, balance disturbance, weakness or numbness in the face and headache. Less commonly there may be difficulty swallowing. Symptoms may worsen gradually over several years, or onset may be sudden.
Complications
Some tumors cause no symptoms at all. Larger tumors may cause more problems, although the size is not always related to the symptom severity. Potential complications include permanent hearing loss, facial numbness, facial weakness, vertigo, and clumsy gait. Severe cases may lead to loss of vital functions, which is life-threatening.
Causes & Risk Factors
The causes of acoustic neuroma are unknown. In a small number of cases, it is associated with the genetic disorder neurofibromatosis type 2. There is concern that heavy cell phone use may be associated with increased risk of developing acoustic neuroma, particularly on the side of the head where the cell phone is most commonly used, but studies are inconclusive, and this topic remains controversial.
Diagnosis & Treatment
A doctor may diagnose acoustic neuroma based on a patient's symptoms, a hearing test and an MRI. Other possible tests include a CT scan, electronystagmography (ENG) or brainstem auditory evoked response (BAER). Initial treatment may be to observe the tumor and monitor its growth. If warranted, surgery may be performed to stop the tumor's growth or remove the tumor completely.
References
- Merck Manual: Acoustic Neuroma
- MD Consult; Acoustic Neuroma; James L. Demetroulakos, M.D., F.A.C.S., et. al.; 2010
- Mayo Clinic: Acoustic Neuroma
