Pre- and post-operative semicircular canal function evaluated by video head impulse test in patients with vestibular schwannoma

Objectives: To evaluate pre- and post -operative semicircular canal function in patients with vestibular schwannoma (VS) by the video Head Impulse Test (vHIT). Methods: Nineteen patients with VS who underwent surgery were enrolled in this study. The gain in vestibuloocular reflex (VOR) and the degree of scatter in catch-up saccades were examined pre- and post -operatively for the semicircular canals in VS patients. Results: Ten of 19 cases (52.6 %) with VS were defined as demonstrating both superior vestibular nerve (SVN) and inferior vestibular nerve (IVN) impairment from the results of pre -operative vHIT. Hearing level and subjective vestibular symptoms showed significant correlations with pre -operative semicircular canal function. Compared to pre -operative vHIT results, VOR gains within 1 month after surgery were significantly reduced in all three canals; however, significant differences had disappeared in the anterior and posterior semicircular canals at 6 months after surgery. Cases of unknown origin had a significantly greater reduction in posterior semicircular canal function after surgery compared with those with disease of IVN origin. Conclusions: As vHIT could evaluate pre -operative vestibular nerve impairment, post -operative VOR gain reduction and the degree of vestibular compensation, semicircular canal function evaluated by vHIT provides a good deal of useful information regarding VS patients undergoing surgery compared to caloric testing, and vHIT should be performed pre- and post -operatively for patients with VS.