Acoustic Neuroma

Description

Acoustic neuromas (vestibular schwannomas) are slow-growing, benign, intracranial, extra-axial tumors originating from the vestibulocochlear nerve.

• Originated from Schwann cells of the nerve sheath
• Usually arise in the internal auditory canal near the cerebellopontine angle
• Most are unilateral; bilaterally seen in neurofibromatosis type 2 (NF2)

Epidemiology

• 6–10% of all intracranial tumors
• 80–90% of cerebellopontine angle tumors
• 95% of cases are unilateral.
• Present most commonly in the 5th to 6th decades, although signs and symptoms can occur earlier
• Female predominance
• 5% of acoustic neuromas are a result of NF2.
• Bilateral acoustic neuroma occurring in NF2 present before age 30 years

Incidence

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

Prevalence
3,000 diagnosed annually in the United States

Etiology and Pathophysiology

• Compression of acoustic and facial nerve when located within internal acoustic canal
• Compression of brainstem, 4th ventricle, and trigeminal nerve when tumor is at the cerebellopontine angle
• Vestibular schwannomas are related to the NF2 gene and its product merlin. Merlin acts as a tumor suppressor and as a mediator of contact inhibition. Thus, deficiencies in both NF2 genes lead to vestibular schwannoma development.

Genetics

• Unknown for unilateral acoustic neuroma
• NF2: bilateral acoustic neuromas
  • Autosomal dominant
  • Gene located on chromosome 22q11

Risk Factors

• High-dose ionizing radiation
• Pregnancy and epilepsy may increase risk.
• There is some literature suggesting that smoking cigarettes may be protective. However, further research must be conducted to support these claims.
• No proven increase in risk of acoustic neuroma with regular use of a mobile phone

Commonly Associated Conditions

• NF2
• Pregnancy may accelerate the growth of the tumor.