MR imaging of lumbar facet joint synovial cysts

The increasing application of magnetic resonance (MR) imaging of the spine has raised the awareness of lumbar facet synovial cysts (LFSC). This well r ecognised, yet uncommon condition, presents with low back pain and radiculo pathy due to the presence of an extradural mass. The commonest affected lev el is L4/5 with a mild degenerative spondylolisthesis a frequent associated finding. MR imaging is the technique of choice to detect and diagnose a LF SC. This pictorial essay, drawing on experience of 43 cases seen in 40 pati ents, illustrates the spectrum of appearances that can be encountered and s uggest differing causes for the variable signal characteristics exhibited. Computed tomography (CT) can be of value in some cases to aid interpretatio n of the MR images. In addition, CT facet arthrography by injection of air or iodinated non-ionic contrast medium may be used to confirm the diagnosis in doubtful cases as well as noting whether the patients presenting sympto ms can be provoked. A comprehensive review of the existing literature is pr esented.