An acoustic neuroma, also called a vestibular schwannoma, is a benign primary intracranial (inside the skull) tumor of the myelin (nerve sheath)-forming cells of the vestibulocochlear nerve (Cranial Nerve VIII). The term "acoustic neuroma" is a double misnomer. The correct medical term is vestibular schwannoma, because it involves the vestibular portion of the 8th cranial nerve and it arises from Schwann cells, which are responsible for the myelin sheath in the peripheral nervous system The usual tumor in the adult presents as a solitary tumor, originating in the nerve. It usually arises from the vestibular portion of the 8th nerve, just within the internal auditory canal. As the tumor grows, it usually extends into the posterior fossa (depression) to occupy the angle between the cerebellum and the pons (cerebellopontine angle). Because of its position, it may also compress the 5th, 7th, and less often, the 9th and 10th cranial nerves. Later, it may compress the pons and lateral medulla, causing obstruction of the cerebrospinal fluid and increased intracranial pressure.