Acoustic Neuroma

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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.

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