Spinal extradural arachnoid cyst.

Spinal extradural arachnoid cysts are rare expanding lesions in the spinal canal. They usually present with progressive signs and symptoms caused by spinal cord compression if they enlarge. A comprehensive review about spinal extradural arachnoid cyst is made including the author's own case of a 59-year-old woman with a 6-month history of progressive back pain radiating to both legs. Key points concerning the possible pathogenesis including symptomatology, diagnosis, and the implications for treatment are highlighted. Surgical treatment is curative and this rare clinical entity should be considered in the differential diagnosis of spinal extradural lesions.