Ipsilateral Saccade Hypometria and Contralateral Saccadic Pursuit in a Focal Brainstem Lesion: a Rare Oculomotor Pattern.

Eye movement examination may be used to rapidly differentiate peripheral and central vestibular syndromes in patients with acute unsteadiness. The analysis of oculomotor impairments may also support the accurate localization of cerebral lesions, particularly those in the brainstem, that are often loosely defined by cerebral MRIs. Saccades, smooth pursuit, and nystagmus were recorded with video-oculography in a patient who had developed sudden vertigo as a consequence of a focal lesion in the depth of the brachium pontis. The patient had shown a previously unreported pattern of eye movement impairments consisting of (i) ipsilesional hypometric saccades, (ii) contralesional saccadic smooth pursuit, and (iii) unilateral gaze-evoked nystagmus. These symptoms enabled the precise localization of the trajectory of pontocerebellar saccadic tracts in the depth of the brachium pontis. We propose that this rare association resulted from a disruption of cerebellar afferents of saccadic pathways and of cerebellar efferents of horizontal smooth pursuit pathways. This reported case emphasizes the crucial role of careful bedside oculomotor examination in order to discriminate between peripheral and central vestibular syndromes in the diagnosis of sudden vertigo. Moreover, it reveals an exceptional pattern of oculomotor impairments that may allow for the precise localization of the trajectory of cerebellar saccadic afferent pathways in the depth of the brachium pontis.