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
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
Exam Important
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
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