ACOUSTIC NEUROMA

• Synonym: Vestibular Schwannoma or Neurilemmoma or 8th Nerve tumor

Origin

• in the internal auditory canal from the inferior or superior portion of the vestibular nerve
• 80% of all Cerebello-pontine angle tumors
• 10% of all intracranial tumors
• Benign encapsulated, extremely slow growing tumors
• Bilateral tumors seen in neurofibromatosis  type 2 (NF2), a syndrome resulting from a chromosome 22 mutation.
• Tumors almost always arise from the Schwann cells of the vestibular division of VIII nerve

Classification based on size

• Intracanalicular (confined to internal auditory canal)
• Small size (< 1.5 cm)
• Medium size (1.5 — 4 cm)
• Large size (> 4 cm)
• Age group: 40-60 years
• No sex predilection

Cochleovestibular symptoms

• • Earliest symptoms –Unilateral sensorineural deafness
  • The three most common presenting symptoms include insidious hearing loss, high-pitched tinnitus, and disequilibrium
  • Difficulty in understanding speech out of proportion of pure tone hearing loss (characteristic of AN)

Cranial nerves

• • 5th nerve earliest to be involved
  • Reduced corneal sensitivity, numbness and paresthesia of face
  • Superior division of vestibular nerve – most common site of AN

Facial nerve involvement

• • Hitzelberger’s sign (hypoaesthesia of posterior meatal wall
  • Loss of taste
  • Decreased lacrimation

Investigations

• • Pure tone audiometry — SNHL more marked in higher frequencies
  • Speech audiometry – Poor speech discrimination and Roll over phenomenon
  • Recruitment absent
  • Short Increment Sensitivity Index (SISI) shows a score of 0-20%
  • Threshold tone decay — retrocochlear type of lesion
  • Diminished or no response to calorie tests.
  • Gold standard for diagnosis: MRI with gadolinium enhancement

Treatment –

• surgical removal, gamma knife or Cyber knife surgery
• Auditory brainstem implant (ABI) – ideal intervention for bilateral acoustic neuromas