[A huge retrocerebellar arachnoid cyst with syringomyelia: case report].

: The authors report a case of a huge posterior fossa arachnoid cyst with syringomyelia. This 22-year-old man presented with a history of drop attacks. Magnetic resonance imaging demonstrated ventricular hydrocephalus, a huge posterior fossa arachnoid cyst and syringomyelia. Cyst-peritoneal shunting was installed. The patient had an uneventful postoperative course, and his drop attacks disappeared. Magnetic resonance imaging one month after surgery showed reduction of the ventricular size and size of the arachnoid cyst and syrinx. Large arachnoid cysts in the posterior fossa are reported occasionally, but rare with syrinx. The authors described this case to illustrate the possible contribution of the pathogenesis of the syringomyelia associated with a huge posterior fossa arachnoid cyst.