A vestibular schwannoma, often called an acoustic neuroma, is a benign primary intracranial tumor of the myelin-forming cells of the vestibulocochlear nerve (CN VIII). The term “vestibular schwannoma” involves the vestibular portion of the 8th cranial nerve and arises from Schwann cells, which are responsible for the myelin sheath in the peripheral nervous system. Approximately 3,000 cases are diagnosed each year in the United States with a prevalence of about 1 in 100,000 worldwide. It comprises 5-10% of all intracranial neoplasms in adults. Incidence peaks in the fifth and sixth decades and both sexes are affected equally.
Contrast-enhanced CT will detect almost all acoustic neuromas that are greater than 2.0 cm in diameter and project further than 1.5 cm into the cerebellopontine angle. Those tumors that are smaller may be detected by MRI with gadolinium enhancement. Audiology and vestibular tests should be concurrently evaluated using air conduction and bone conduction threshold testing to assess for sensorineural versus conduction hearing loss.