Symptomatic isolated lumbar interdural arachnoid cyst.

A 72-year-old man presented with an extremely rare case of symptomatic isolated lumbosacral interdural arachnoid cyst manifesting as pain and weakness in the right buttock and lower extremity that had aggravated for 2 weeks. Although the surgical strategy for the interdural cyst was not complicated, the origination of the cyst was not clearly understood. Surgery found an isolated membrane of the cyst inside double-layered dura without communication with the intact arachnoid membrane. Cerebrospinal fluid with hemorrhage accumulated within the interdural cyst indicated recent bleeding into the cyst. Our experience suggests that this cyst was congenital based on the surgical results and imaging studies.