Fascicular arrangement within the oculomotor nerve MRI analysis of a midbrain infarct

The fascicular arrangement of the oculomotor nerve within the midbrain is n ot adequately elucidated in humans. We treated a patient with a partial ocu lomotor palsy who had impaired adduction and supraduction on the left side, which were attributed to an ipsilateral lacunar infarct, CT and MRI reveal ed a discrete lesion in the centre of the midbrain tegmentum in the rostroc audal plane. This case suggests that the oculomotor fibres for extraocular movement are located in the middle of the the midbrain, and supports the fa scicular proximity of the superior and medial rectus muscles. The fascicula r arrangement of the midbrain oculomotor nerve is speculated to be pupillar y component, extraocular movement and eyelid elevation in that rostrocaudal order, based on the previous reports of neuro-ophthalmological impairment and MRI findings, which are analogous to the nuclear arrangement proposed b y Warwick, (C) 2000 Harcourt Publishers Ltd.