Otolith function after acoustic neuroma surgery

The response of the vestibular system after acoustic neuroma surgery was in vestigated in nine patients. The otolith system was studied by means of ocu lar counterrolling, assessed by video oculography. Horizontal vestibulo-ocu lar reflex (VOR) function was tested by the sinusoidal harmonic acceleratio n test using electronystagmography. The results were compared with those ob tained from a normal control population. The response to slow rotation test s was symmetric, but the gain was significantly reduced when compared to th e normal population. Phase lag was significantly increased. No difference i n ocular torsion was observed with lateroflexion of the head to the ipsilat eral side in comparison with lateroflexion to the contralateral side. Moreo ver, the overall ocular counterrolling was well within normal limits. We co nclude that the semicircular canal response differs from the otolith respon se. The component of the torsional VOR mediated by otolith stimulation appe ars to be more robust than the horizontal VOR mediated mainly by the horizo ntal semicircular canal system. Ocular counterrolling induced by lateroflex ion does not reveal abnormalities in patients with surgically produced unil ateral peripheral loss.