Synovial cysts and ganglia can arise from any synovial-lined articulation or tendon sheath, affected by osteoarthritis or rheumatoid arthritis. They are encountered predominantly in the extremities, especially at the wrist and knee. However, they can be associated with any diarthrodial joint in the body. The disease is caused by cystic dilatation of the synovial membrane of the joints. Compared with the number of lesions involving the extremities, spinal localization is considered a rare finding. Nevertheless, over the last few years, synovial cysts of the spine have been increasingly reported, probably due to the availability of high-quality CT and MRI . Intraspinal development of this kind of cystic lesion may be asymptomatic or responsible for back pain and neurological disorders. Classically, there is a predilection for these cysts to develop at the L4–L5 facet joint, which is known to be the most mobile segment and the point of maximum axial loading of the spine. This particular predilection for cysts to occur adjacent to the L4–L5 facet joints has also been attributed to the amount of degenerative spondylosis at that level of the spine. Synovial cysts can also be detected in the presence of L4–L5 degenerative spondylolisthesis .
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