Disease 05.6

Vestibular Schwannoma

MRI remains the diagnostic standard, but VEMP has practical sensitivity around 80% and can localise the affected vestibular division.

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Foundation

What is a vestibular schwannoma?

A vestibular schwannoma (formerly called an acoustic neuroma) is a benign tumour arising from the Schwann cell sheath of the vestibular nerve, usually within the internal auditory canal. The classic presentation is unilateral progressive sensorineural hearing loss with tinnitus; vertigo is less common but possible.

AudiogramThe pure-tone signature
1252505001k2k4k8kFrequency (Hz)020406080100dB HLRL
Progressive, asymmetric, downsloping sensorineural hearing loss with disproportionately poor word recognition is the audiometric red flag for a vestibular schwannoma. Any clear asymmetry > 15 dB across two consecutive frequencies — particularly with poor speech audiometry — earns an MRI.
01020304050Time (ms)NormalSchwannoma (affected ear)
Absent or markedly reduced VEMP on the affected side is the most common pattern, particularly with extracanalicular extension.
Trainee

VEMP findings

  • Absent or reduced amplitude on the side of the tumour.
  • Increased IAR.
  • Prolonged latency is occasionally seen (retrocochlear lesion).
  • Pattern depends on which division the tumour originates from — most schwannomas arise from the inferior vestibular nerve, so cVEMP abnormalities tend to predominate.
Clinician

Diagnostic value

MRI with gadolinium remains the diagnostic gold standard. The role of VEMP is (1) functional characterisation of nerve involvement when imaging is ambiguous, (2) baseline assessment before "watch and wait" or treatment, and (3) monitoring during conservative management.[23]

Tumour size correlates with VEMP abnormality: small purely intracanalicular tumours may produce only subtle changes, while larger lesions with cerebellopontine angle extension more often produce absent VEMPs.[23]

Reading the report

A patient with unilateral hearing loss and an absent cVEMP — but a normal caloric and oVEMP — has a pattern suggestive of inferior vestibular nerve involvement. This is the most common topographic finding in schwannoma and warrants MRI even when the hearing loss looks "cochlear" by audiometry alone.