The appearances of lumbar intraspinal synovial cysts

Intraspinal synovial cysts most commonly occur in the lower lumbar spine and may cause radicular symptoms. Eight symptomatic patients are described, each of whom had a single synovial cyst with associated facet joint degeneration. Four were at the L4-5 level and two each at L3-4 and L5-S1. Myelography in four patients revealed a posterolateral indentation on the contrast column in each case. Computed tomography (CT) revealed a structure of similar or greater density than the thecal sac in six cases and of gas density in one case. Two of the former cases also contained gaseous elements, three cases had a mildly dense rim and in the eighth case calcification was demonstrated within the cyst. One cyst resolved after facet joint injection with local anaesthetic and steroid.