VERTICAL AND TORSIONAL VOR IN POSTERIOR CANAL OCCLUSION

The vertical and torsional vestibule-ocular reflexes (VOR) were invest igated in 3 patients with surgical occlusion of the posterior semicirc ular canal and 1 patient with singular neurectomy. for treatment of re fractory paroxysmal positional vertigo. Stimuli comprised sinusoidal o scillation 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 vert ical and torsional VOR gain was seen 1 week postoperatively when the o ccluded canal was placed in the optimal plane for stimulation at 1 wee k 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 unste adiness in this case, The other 3 cases who were investigated postoper atively all showed a decrease in downward VOR gain in the 'on' directi on of the operated canal. The data indicate the specificity of the tes t procedure and underline the prognostic value of comprehensive pre-op erative vestibular assessment.