Ligamentum flavum cyst of lumbar spine: a case report and literature review.

Ligamentum flavum cysts have rarely been reported and known to be the uncommon cause of spinal compression and radiculopathy. A 63-year-old man presented right sciatica lasting for 1 month. Lumbar computerized tomography and magnetic resonance imaging demonstrated an extradural cystic mass adjacent to the L5-S1 facet joints. Partial hemilaminectomy and flavectomy at the L5-S1 space were performed, and then the cystic mass was excised. Histopathology confirmed a connective tissue cyst, which is consistent with the ligamentum flavum. Microscopic examination of the cyst wall revealed that it is closely packed collagen fibril. The symptom of patient was improved after surgery. Because of rarity of ligamentum flavum cysts and nonspecific clinical and radiologic findings, the preoperative diagnosis is not easy. The histologic features of ligamentum flavum cysts are distinct from other cystic lesion of lumbar spine. This study presents a case and literature review of ligamentum flavum cyst. We summarize the pathophysiology, occurrence, differential diagnosis of rare ligamentum flavum cyst, especially on lumbar spine.