Investigations

In a patient suspected of having an acoustic neuroma, the following tests are of value:

• neuro-otological:
  • pure tone audiometry - demonstrates unilateral sensorineural hearing loss
  • brainstem audiometry - to distinguish cochlear deafness from retrocochlear disease
  • o speech discrimination test (1)
  • caloric test - expect depressed or absent response
    
    
• CT - need contrast since acoustic neuromas are often isodense:
  • intravenous iodinated water soluble contrast (1)
  • metrizemide contrast into the basal cisterns or intrathecal air run up to the cerebellopontine angle clearly identifies small acoustic neuromas
    
    
• MRI - especially for small intracanalicular tumours. With gadolinium - DTPA enhancement, this test is very sensitive and may demonstrate lesions of 1-2 mm in diameter within the auditory canal
  • T2-weighted images
  • contrast enhanced T1-weighted images - the sensitivity is increased by the gadolinium-based contrast medium and it can demonstrate small neuromas and intralbyrinthine lesions (2)
    
    
• tomography of the internal auditor meatus - if no CT/MRI

Reference:

• (1) British association of otorhinolaryngologists 2002. Clinical effectiveness guidelines, Acoustic neuroma (vestibular schwannoma)
• (2) Ramnarine Devindra, Whitfield Peter. Management of patients with vestibular schwannoma. ACNR 2005; 5(4).