• Slow-growing benign tumor, most often arising from the vestibular division of 8th cranial nerve
• Originates from Schwann cells of the nerve sheath (“schwannoma”)
• Usually arises in the internal auditory canal near the cerebellopontine angle
• Often has extracanalicular portion into the cerebellopontine angle, but may also stay purely intracanalicular
• Most are unilateral; bilateral only seen in neurofibromatosis type II

• 6–10% of all intracranial tumors
• 80–90% of cerebellopontine angle tumors
• 95% of cases are unilateral
• Present most commonly in the 5th–6th decade
• Female predominance
• Bilateral acoustic neuroma occurring in neurofibromatosis II present before age 30

Incidence

• 1/100,000 per year
• Asymptomatic lesions may be more common

Prevalence 3,000 diagnosed annually in the US

• Pregnancy and epilepsy may increase risk (1).
• Smoking may decrease the risk (1).

Genetics

• Unknown for unilateral acoustic neuroma (AN)
• Neurofibromatosis type II: Bilateral ANs:
  • Autosomal dominant
  • Gene located on chromosome 22q1

• Exerts pressure on the surrounding structures
• Compression of acoustic and facial nerve when located within internal acoustic canal
• Compression of brainstem, 4th ventricle, and trigeminal nerve when tumor at the cerebellar pontine angle

Unknown

• Neurofibromatosis type II
• Pregnancy may accelerate the growth of the tumor