Vertical one-and-a-half syndrome. Supranuclear downgaze paralysis with monocular elevation palsy.

A patient with bilateral infarction in the mesodiencephalic region showed impairment of all downward rapid eye movements (including vestibulo-ocular movements) and foveal smooth pursuit (nondissociated downgaze paralysis) associated with monocular paralysis of elevation (vertical one-and-a-half syndrome). Bell's phenomenon and all types of horizontal eye movements were preserved. The lesions may have affected the efferent tracts of the rostral interstitial nucleus of the medial longitudinal fasciculus bilaterally and the premotor fibers to the contralateral superior rectus subnucleus and ipsilateral inferior oblique subnucleus, either before or after decussation in the posterior commissure.