Acute extradural compression due to an intraspinal synovial cyst: CT and myelogram appearances.

Intraspinal synovial cysts, sometimes referred to as ganglion cysts, are uncommon entities thought to be related to degenerative changes of the facet joints. They usually present with low back pain and sciatica of months or years duration. We report a case of acute extradural compression in a previously asymptomatic patient demonstrated on myelography and computed tomography to be due to a cystic lesion related to the apophyseal joint, shown at operation to be a synovial cyst. The literature on this condition is reviewed.