[Oculomotor disturbances as cerebellar symptoms in pontine angle tumors. Contralateral diminution of optokinetic nystagmus as early sign of floccular lesions (author's transl)].

Spontaneous eye movements and responses to visual and vestibular stimuli were recorded in 30 patients with pontine angle tumors (26 neurinomas, 2 meningeomas, 1 chosteatoma, 1 angioma). Pre- and postoperative recordings in most cases showed a bilateral dimunition of horizontal optokinetic nystagmus (OKN) that prevailed towards the side contralateral to the tumor. This is explained by a homolateral floccular lesion and cannot be the consequence of spontaneous nystagmus or asymmetrical gaze nystagmus. The predominance of a homolateral OKN-diminution often described in the literature was found in advanced cases or post-operatively as a sign of pontine reticular formation damage. The neighbourhood of the flocculus to the VIIIth nerve and animal experiments with floccular lesions causing a contralateral OKN diminution support out explanation. Additional arguments for damage of cerebellar oculomotor functions are the predominance of cogwheeled smooth pursuit and the occasional observation of hypermetric saccades, both toward the side of the tumor. Patients with very large tumors finally develop a complete disruption of OKN toward the homolateral side together with concomitant gaze paralysis.