Acute hemorrhagic cyst of the ligamentum flavum.

STUDY DESIGN: A case report and clinical discussion. OBJECTIVE: To describe a rare complication of a cyst of the ligamentum flavum, which bled spontaneously, provoking an acute lower limb monoparesis and lumbar sciatic pain. SUMMARY OF BACKGROUNDS DATA: Cysts of the ligamentum flavum have been rarely reported. Intraspinal degenerative cysts described in literature are usually juxta-articular (synovial and ganglion) cysts and have a similar radiologic appearance. They are preferentially located in the lumbar spine, while the cervical localization is unusual. Hemorrhage into the cyst is an uncommon complication and an extremely rare cause of nerve root compression. METHODS: A 59-year-old woman presented with sudden severe radicular lumbar deficit and pain secondary to acute hemorrhage into a ligamentum flavum cyst. Magnetic resonance imaging showed at L3-L4 level a lobulated slightly hyperintense mass with a ventral area of marked hyperintensity in T1 images, hypointense on T2 images. Signal within the lesion was suggestive of intralesional hemorrhage. RESULTS: Complete resection of the lesion was performed, resulting in immediate recovery. The cyst was quite rounded, brownish, and contained rest of both partially fresh and coagulated hematoma. Histologic examination revealed myxoid degeneration of the ligamentum flavum with an hemorrage in the cystic cavity without a synovial layer. CONCLUSIONS: This report identifies a rare case of radicular lumbar deficit and pain secondary to acute hemorrhage into a ligamentum flavum cyst. The pathogenesis and clinicopathologic characteristics of this lesion are described.