Unilateral oculomotor nerve palsy: unusual sign of hydrocephalus.

We report an unusual case of hydrocephalus in which unilateral oculomotor nerve paralysis was the predominant sign. Misinterpretation of such an atypical clinical sign may lead to inappropriate therapy. We outline the role of intracranial pressure monitoring as an adjunctive diagnostic tool and we suggest a presumptive mechanism to explain the correlation between enlarged ventricles and 3(rd) nerve dysfunction. A 16-year-old boy presented with a complete left oculomotor nerve palsy associated with imaging findings of dilated ventricles and Dandy-Walker variant cystic malformation. Monitoring of intracranial pressure through a ventricular catheter was undertaken. In the first phase (no cerebrospinal fluid drainage [CSF] drainage) mean intracranial pressure (ICP) values were >0 mmHg. A second phase (with progressively longer CSF draining) further defined the diagnosis. A ventriculo-peritoneal shunt was then placed and the nerve function returned to normal within few days. Third cranial nerve dysfunction as a predominant sign of hydrocephalus is very rare and may raise doubts as to the real significance of the imaging findings of enlarged ventricles. In this ground, ICP monitoring is a safe and helpful diagnostic tool that can afford a more accurate evaluation and proper treatment. The supposed mechanism of 3(rd) nerve dysfunction was bending/stretching of the nerve.