An acoustic neuroma is a type of benign (noncancerous) brain tumor that grows on the vestibular nerve as it travels from the inner ear to the brainstem. It is one of the most common types of benign brain tumors. The first sign of one is usually hearing loss.
The cochleo-vestibular nerve (also called the eighth cranial nerve) is made up of three nerves that connect the inner ear to the brain. One branch — the cochlear nerve — carries hearing information. The other two branches — the inferior and superior vestibular nerves — carry balance information to the brain. The nerves are wrapped in a layer of specialized cells called Schwann cells. An acoustic neuroma — also called a vestibular schwannoma — is a tumor of those cells. If an acoustic neuroma is not diagnosed or treated it can grow large enough to press on important structures in the brainstem and cause major life threatening problems.
The main symptoms of an acoustic neuroma are hearing loss and tinnitus (ringing in the ears). They are caused by the tumor pressing on the auditory nerve. Although the tumor actually grows on the balance nerve, imbalance is usually mild or absent. Since we have two balance systems, the opposite side can compensate for the slow progressive loss caused by the tumor.
These tumors have been linked to a mutation in a protein that regulates tumor suppression. In most cases the tumor grows only on one side of the head and is diagnosed between the ages of 30 and 50. Acoustic neuromas in children are very rare. People with a hereditary disease called neurofibromatosis type 2 develop bilateral acoustic neuromas because they lack the tumor suppressor protein merlin. About 10% of all acoustic neuromas occur in people with neurofibromatosis.