Brain Tumour Award funded by Brian Quilty Memorial Fund, Carol & Stacey Buckley and Phyllis Edith Chard Estate
Vestibular-postural responses in pre and post operative follow-up of cerebellopontine angle tumours.
Dr Miriam Welgampola
Central Clinical School, University of Sydney
Co-Investigator: Professor Brian L. Day
Vestibular schwannomas are slow-growing tumors arising from the vestibular nerve. They can be incidentally discovered or may present with hearing impairment, tinnitus, or imbalance. Their natural history ranges from spontaneous involution to rapid growth. Since the tumor may remain unchanged in size for years following diagnosis, a careful follow-up by MRI (‘‘wait and scan’’) approach has emerged towards patients with small and medium-sized tumours. In this study, we first seek a physiological measure that will be a useful follow-up tool for longitudinal assessment of patients with schwannomas who are being managed conservatively.
Upon surgical removal of a schwannoma, there is partial or complete section of the vestibular nerve. A proportion of patients develop post-operative vertigo and disequilibrium. Symptoms are severe for patients who had smaller tumors and relatively intact vestibular nerves (who face a precipitous change in vestibular function due to surgery); in contrast, subjects with larger tumors in whom the vestibular nerves were slowly destroyed due to the Schwannoma are relatively asymptomatic. Overall, early post-surgical rehabilitation promises a good outcome in terms of postural stability.
A low intensity (0.5-1mA) cathodal electrical pulse delivered over the mastoid process activates the terminal endings of the vestibular nerves. An increase in the firing rate of the nerve produces a sensation of falling in the direction of the stimulated ear. A compensatory body sway occurs in the opposite direction. The direction and magnitude of body sway can be quantified in 3 dimensions. Galvanic vestibular stimulation offers a safe and simple means of testing vestibulospinal pathways to the trunk and limbs.
Although a few centers offer brief in-hospital pre- and post-surgical rehabilitation (lasting the duration of stay), it is not feasible to refer all patients undergoing shwannoma surgery for intensive rehabilitation lasting weeks. This project will develop a reflex measure that will identify an “at risk” population for post surgical disequilibrium who can be offered intensive rehabilitation. Vestibular Schwannomas also provide an excellent disease model for studying selective vestibulopathy affecting the superior and inferior vestibular nerves. Our work will help validate a quantitative and lateralizing test of the vestibular projections to the trunk and limbs. This technique will be useful in the assessment of disorders of stance and gait which are a debilitating manifestation of vestibular disease.