Isolated unilateral infarction of the cerebellar tonsil: ocular motor findings.

The oculomotor abnormalities with isolated infarction of the cerebellar tonsil are unknown. In a patient with acute infarction of the right tonsil, we found (1) nearly completely abolished ipsilateral smooth pursuit and impaired contralateral pursuit, (2) a low-amplitude ipsilesional right-beating nystagmus without fixation, (3) gaze-holding deficits, and (4) normal vestibulo-ocular reflex. These findings contrast with striking vestibular abnormalities reported with unilateral flocculus and anterior tonsil infarction.