Vestibular schwannoma

From Ganfyd

Also known as an acoustic neuroma, a vestibular schwannoma is the commonest type of cerebellopontine (CPA) angle tumour. They represent 80% of all CPA tumours, and 8% of all intracranial tumours.

Aetiology

• Incidence 1 in 100,000
• Equal sex distribution
• Present between the ages of 40-60
• 5% are bilateral
• Associated with Neurofibromatosis type 2, especially if bilateral

Pathology

• Arise most commonly from the superior vestibular nerve
• Originate at the junction of glial cells and schwann cells
• Two histological types
  • Fasciculated - packed sheaves of connective tissue cells
  • Reticular - disorderd loose network of cells with intercellular vacuoles and cysts
• Tumour appears as yellow encapsulated mass with nerves splayed out on surface

Clinical Features

• Otological symptoms
  • Progressive sensorineural deafness (90%)
  • Tinnitus (70%)
  • Vertigo is unusual symptom
  • Hitselberger's sign is positive
• Trigeminal nerve involvement
• Headache
• Neurological symptoms
  • Represent later presentation
  • Facial weakness or spasm
  • Ataxia
  • Diplopia
  • Papilloedema
  • Reduced level of consciousness

Investigations

Imaging is most important. Gadolinium enhanced MRI is the gold standard investigation. Pure tone audiometry shows a sensorineural hearing loss. Brainstem evoked response audiometry shows an increase latency between waves N1 and N5.

Management

Vestibular schwannomas are slow growing tumours. Annual MRI scans show that 60% do not increase in size. Conservative management, especially in the elderly, may be appropriate.

Surgery is associated with injury to the VIIth and VIIIth cranial nerves. CSF leaks and meningitis are occasional side effects. There are three traditional approaches.

• Translabyrinthine approach
  • Preserves facial nerve
  • All hearing is lost
• Middle fossa approach
  • Better for smaller tumours
  • Preserves hearing
  • High (15-20%) risk of developing epilepsy. Drivng in banned for 1 year following this procedure in the UK
• Retrosigmoid approach
  • For more medially placed tumours only
  • Can preserve both facial nerve and hearing

Alternatively, a precise arrangement of radiation sources publicised as the "gamma knife" can be used.

Further Reading

• NJ Roland, RDR McRae, AW McCombe. Key Topics in Otolaryngology. Second edition. BIOS Scientic Publishers Ltd, Oxford. p1-4