Parinaud's syndrome: electro-oculographic and anatomical analyses of six vascular cases with deductions about vertical gaze organization in the premotor structures.

Six cases of Parinaud's syndrome, with downward (Cases 1, 2), upward (Cases 3, 4) and both downward and upward gaze paralysis (cases 5, 6) are reported. Four cases (Cases 1, 2, 3, 5) were studied anatomically using serial sections of the brain and 3 cases (Cases, 1, 4, 6) analysed electro-oculographically. In all the cases there were rather small vascular lesions in the mesodiencephalic region, sparing the oculomotor nuclei. Since the rostral interstitial nuclei of the medial longitudinal fasciculus (riMLF), located above the oculomotor nuclei, contain the final relays producing all vertical saccades, it is suggested that the different aspects of Parinaud's syndrome may result from damage to their cells or to their excitatory efferent tracts, or even to their afferent pathways. Downgaze paralysis results from bilateral lesions involving the regions located just caudal, medial and dorsal to the upper poles of the red nuclei. The critical area is probably related to the mediocaudal part of the riMLF, the lateral portion of which appears to be spared. These anatomical data, combined with the clinical observation that most downward eye movements (except slow reflex movements) are affected in the case with such paralysis, lead us to propose that it is the riMLF efferent tracts mediating downgaze and projecting on to the oculomotor nuclei that are principally damaged by the lesions. Upgaze paralysis results from unilateral lesions in or near the posterior commissure. The clinical data allow us to propose that it is also the riMLF efferent tracts, mediating upgaze, that are damaged in such cases. consequently these tracts, probably originating from the dorsolateral part of the riMLF, would decussate through the posterior commissure before they reach the oculomotor nuclei. Combined downgaze and upgaze paralysis results from bilateral lesions involving the region related to the whole riMLF on both sides. The principal conclusion is that the riMLF efferent tracts mediating upward and downward gaze have clearly separate courses in the immediate premotor structures.