The lack of correlation between the size of vestibular schwannoma (VS) and degree of hearing loss and vestibular function tests is well known. In this retrospective study, the focus was on the correlation between VOR gain of semicircular canal function, as assessed by vHIT, and various features of VS. Twenty four subjects with VS, median age of 66 years (range 46-83) were included in the study. In all three semicircular canals, the mean VOR gain was lower in the affected ear compared to the unaffected ear (p = 0.019, 0.003 and 0.009 for anterior, horizontal and posterior canals respectively). In fact, the gain in the unaffected ears was normal. It was no surprise that there was no correlation between mean VOR gain and age, duration of disease, size and grade of tumour. The authors reported a significant negative correlation between VOR gain and hearing loss. The greater the hearing loss, the lower the VOR gain, more in the horizontal canal than in the posterior canal. Further analyses showed that the presence of catch up saccades correlated significantly with poorer hearing in the horizontal canal but not in the posterior canal.
Citing previous studies, the authors conclude that impaired vestibular function is most likely multifactorial rather than due to the compressive effect of the tumour.
There may well be yet to be studied cellular mechanisms at play.