Vestibular schwannoma
A benign tumour of the Schwann cells of CN VIII, usually originating from the inferior vestibular nerve. Slow growth is its defining feature — and the reason the RCT can look gentler than the imaging suggests.
Clinical picture
Progressive asymmetric high-frequency sensorineural hearing loss with tinnitus is the commonest presentation. Vertigo is uncommon; mild chronic unsteadiness is more typical. Larger tumours produce facial sensory disturbance, ataxia and headache from cerebellopontine-angle compression BalanceMD Clinical Group. 2024.
Pathophysiology
The tumour grows from the Schwann cells of the vestibular divisions of CN VIII. The inferior division is most often the origin, but symptoms can affect either or both divisions plus the cochlear nerve as the tumour enlarges. Continuous slow growth allows the central vestibular system to recalibrate gain and re-balance tone as the lesion progresses, which is why many patients have surprisingly subtle balance complaints.
RCT pattern
| Step Tc | 12.0 s |
|---|---|
| Step gain | 0.60 |
The classical RCT finding is a unilateral pattern: mild gain reduction, modest phase-lead increase, and a small directional preponderance toward the intact side BalanceMD Clinical Group. 2024. The magnitude is often less impressive than a caloric weakness on the same patient — because compensation, not regression, has occurred slowly alongside the tumour's growth.
Diagnosis & differential
- Gadolinium-enhanced MRI of the internal auditory canal is definitive.
- Audiometry and ABR are sensitive screens.
- VEMPs may localise the lesion to the superior or inferior division.
- RCT is helpful for baseline and post-operative comparison rather than for diagnosis itself.