A vestibular schwannoma is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve (8th cranial nerve). A type of schwannoma, this tumor arises from the Schwann cells responsible for the myelin sheath that helps keep peripheral nerves insulated. Approximately 3,000 cases are diagnosed each year in the United States. Most recent publications suggest that the incidence of acoustic neuromas is rising because of advances in MRI scanning. Studies in Denmark published in 2004 showed an annual incidence of 17.4 per million. Most cases are diagnosed in people between the ages of 30 and 60, and men and women appear to be affected equally.It is also commonly called an acoustic neuroma, although this term is technically a misnomer: the tumor rarely arises from the acoustic division of the vestibulocochlear nerve, and it is really a schwannoma rather than a tumor of actual nerve tissue (the literal meaning of the somewhat ambiguous term ""neuroma"").