Synovial cyst--an unusual cause of nerve root compression. A case report.

An elderly woman presented with a tense, synovia-lined ganglion, associated with the left L3/L4 apophyseal joint, which protruded posteriorly and caudally through the joint capsule and extended anteriorly and cephally into the neural canal. The intraspinal extension produced a compression radiculopathy of the L3 nerve root. Removal of the cyst produced acute and dramatic alleviation of the symptoms.