Acoustic Neuroma / Vestibular Schwannoma / Neurilemmoma / 8th Nerve tumor

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
  1. Classification based on size
  2. Intracanalicular (confined to internal auditory canal)
  3. Small size (< 1.5 cm)
  4. Medium size (1.5 — 4 cm)
  5. 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
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