Vertical and torsional VOR in posterior canal occlusion

The vertical and torsional vestibulo-ocular reflexes (VOR) were investigated in 3 patients with surgical occlusion of the posterior semicircular canal and 1 patient with singular neurectomy, for treatment of refractory paroxysmal positional vertigo. Stimuli comprised sinusoidal oscillation in the coronal ("roll") and sagittal ("pitch") plane as well as in two oblique planes intermediate between pitch in order to stimulate left anterior + right posterior (LARP) and right anterior + left posterior (RALP) canal pairs separately. One case with left side BPPV was investigated pre and post-operatively. Depression of the vertical and torsional VOR gain was seen 1 week postoperatively when the occluded canal was placed in the optimal plane for stimulation at 1 week postoperatively and subsequently gradually recovered. Recordings in other planes suggested that the contralateral posterior canal was also hypofunctioning, a finding which may explain some residual gait unsteadiness in this case. The other 3 cases who were investigated postoperatively all showed a decrease in downward VOR gain in the "on' direction of the operated canal. The data indicate the specificity of the test procedure and underline the prognostic value of comprehensive pre-operative vestibular assessment.