The prevalence and pathogenesis of synovial cysts within the ligamentum flavum in patients with lumbar spinal stenosis and radiculopathy

Abstract

Study Design. A clinicopathologic study of synovial cysts in the ligamentum flavum (LF) in patients with spinal stenosis. Objective. To investigate the pathogenesis of lumbar juxtafacet cysts. Summary of Background Data. Contradictions in the terminology applied to lumbar juxtafacet cysts arise from the frequent sparsity of synovial lining cells, which has led to synovial cysts often being called “ganglion cysts” despite lacking confirmatory pathology. Methods. A total of 27 consecutive patients with radiologically confirmed stenosis underwent laminectomy. LF/facet joint (FJ) relationships were retained by en bloc excision of the LF and the medial inferior FJ. Controls were LF/FJ specimens from 47 cadaver lumbar spines. Results. The 27 patients yielded 51 LF/FJ specimens containing 28 synovial cysts, 12 of which were unilateral and 8 were bilateral. Fragments of articular cartilage and bone were embedded in the walls of 89% of cysts and in the walls of a bursa-like channel originating from the medial aspect of the FJ capsule and extending into the LF. Communication with the FJ via this channel was observed in 21 (75%) of the 28 synovial cysts. Extending up to 12 mm in length, the channel was present in nearly all control spines at the L4–L5 level but in only about half at the T12–L1 level. Conclusion. Cysts having an extensive or meagre synovial cell lining are common in the LF of patients with symptomatic lateral or central stenosis. The cysts communicate with the FJ by a bursa-type channel within the LF. Advanced osteoarthritis of the FJ causes the liberation of fragments of cartilage and bone into the synovial fluid of the joint space. This enables some fragments to escape from the joint into the channel and become lodged within its wall where they provoke granulation tissue and scar formation. The tissue response to articular debris may block the synovial-lined channel to cause synovial cyst formation.