<span class="word">Reduction <span class="word">of <span class="word">the <span class="word"><span class="changedDisabled">Vestibulo-<span class="word"><span class="changedDisabled">Ocular <span class="word">

Background: A group of patients with untreated unilateral vestibular schwannoma (UVS) was observed in previous clinical trials, and the results indicated a reduction in the vestibulo-ocular reflex (VOR) on the side of lesion. However, in a subset of patients, a loss of VOR gain was also observed on the contralateral (non-tumor) side, which may indicate the presence of contralateral neural crosstalk. Methods: To understand our previous clinical findings, the present study has expanded its population to investigate whether these unexpected findings are recognized in a significantly larger population of patients with UVS (n=640). Retrospectively, mean VOR gains of all semicircular canals (SCC) were obtained using video head impulse tests (vHIT) and compared between ipsi- and contralateral side of lesion. To eliminate any potential bias resulting from procedural effects, vHIT data was also obtained from a control group of 72 healthy subjects. Results: As expected, a VOR gain reduction was identified on the side of lesion in a substantial proportion of patients with UVS, varying ranging from 19.4% (anterior SCC) to 39.7% (posterior SCC). More interesting was the observation of a significant proportion of patients (21.9%) exhibiting a significant VOR reduction in posterior semicircular canal on the contralateral side, with a strong correlation with the ipsilateral side (r = 0.70). In relation to this phenomenon, our data further demonstrates that possible crosstalk of the superior branch of the vestibular nerve is of less influence on the contralateral side VOR gains compared to that of the inferior branch. Conclusion: Firstly, a reduced VOR gain in the contralateral posterior semicircular canals was found. Secondly, correlations between the inferior vestibular branches in UVS patients were comparable to the control group. These results may support the interactions such as bilateral commissural connectivity between vestibular nuclei.