Synovial cysts of the lumbar spine--pathological considerations and surgical strategy.

Symptomatic lumbar synovial cysts (LSCs) are a rare cause of degenerative narrowing of the spinal canal, with thecal sac or nerve root compression. True synovial cysts have a thick wall lined by synovial cells, containing granulation tissue, numerous histiocytes, and giant cells. In contrast, pseudo-cysts lack specialized epithelium, have a collagenous capsule filled with myxoid material, and may be classified into ganglion cysts, originating from periarticular fibrous tissues, and ligamentous cysts, arising from the ligamentum flavum or even from the posterior longitudinal ligament. Here we present the surgical series of the Chair of Neurosurgery at the University of Cagliari (Italy) including a total of 17 LSCs. Surgical technique consisted of facet sparing excision of LSC, achieved by simple hemilaminectomy/laminectomy, and diagnosis was always confirmed by histological specimen examination, which detected the typical synovial epithelium, the intracystic presence of hemosiderin, histiocytes, and calcifications. Further immunohistochemical investigation revealed positive staining for cytokeratin: CK5, CK6, and AE1/AE3. Clinically, our cohort experienced rapid and complete resolution of symptoms, without perioperative complications, or recurrence of cysts or vertebral instability at a median follow up of 28 months, when the MacNab score was generally excellent. A review of the literature, retrieving articles published from 1973, collected a total of 101 articles concerning all the cases of LSC scientifically described to date. Both clinical and histological findings described in our study support the theory of degenerative microtraumatic pathogenesis of synovial cysts.