Paradoxical fixed dilatation of the contralateral pupil as a false-localizing sign in intraparenchymal frontal hemorrhage.

Unilateral fixed pupillary dilatation represents an important clinical sign of transtentorial herniation of an ipsilateral mass lesion. Rarely the contralateral pupil is affected to produce a false-localizing sign. Two cases of this paradoxical contralateral fixed pupillary dilatation involving intra-axial lesions have been reported. We report a case of a 33-year-old man with a left frontal intraparenchymal hemorrhage who developed a false localizing fixed dilatation of his right pupil, which resolved after craniotomy and evacuation of the clot. The possible mechanisms of contralateral third nerve palsy are discussed.