Synovial Cysts

      Juxtaarticular synovial cysts are associated with facet arthropathy, generally of fairly severe degree. They consist of a fibrous wall, often with a distinct synovial lining, and a cystic center that may or may not communicate with the facet joint. They are found most frequently at L4-5, the more mobile segment of the lumbar spine. Synovial cysts can compress the dorsal nerve roots and cause radicular symptoms.

      On MR scans, synovial cysts appears as smooth, well-defined extradural masses in the posterolateral spinal canal. They are positioned adjacent to a facet joint and dorsal to or merges with a thickened ligamentum flavum. The cystic center has a highly variable MR signal pattern due to the spectrum of fluid components (serous, mucinous, or gelatinous), air, and hemorrhagic components. The hypointense perimeter reflects the fibrous capsule with calcium or hemosiderin from chronic hemorrhage, as well as the companion joint capsule and adjacent ligaments. Endnote The fibrous capsule may enhance with gadolinium. The combination of proton-density and T2-weighted axial images are best for detecting and delineating these lesions.  

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