Insights into the three-dimensional structure of the oculomotor nuclear complex and fascicles

The authors report the case of a patient with an ischemic lesion in the lef t midbrain. The patient presented with paresis of left inferior rectus, pup il, right superior rectus, convergence and transiently, of the left medial rectus. A lesion in the left dorsal midbrain close to the oculomotor nuclea r complex, selectively involving the fascicles innervating the above muscle s, is proposed. Fine magnetic resonance sections showed a consistent lesion in the left paramedian dorsal midbrain. A detailed, three-dimensional, sch ematic computer model of the oculomotor nucleus and fascicles was construct ed. Using this model, the authors topographically validate the putative sit e of the lesion. The medial rectus subnucleus is divided into three subgrou ps, A, B, and C. Subgroup C is thought to be the site of the majority of ne urons controlling convergence. In the above model, the putative lesion is c loser to subgroup A than to C; this suggests that subgroup A, rather than s ubgroup C, may have a higher concentration of neurons involved in convergen ce.