MR imaging of a hemorrhagic and granulomatous cyst of the ligamentum flavum with pathologic correlation.

Cysts of the ligamentum flavum are uncommon causes of neurologic signs and symptoms and usually are seen in persons over 50 years of age. We report a case of an epidural cyst located in the ligamentum flavum, which contributed to spinal stenosis in a 30-year-old man. Radiologic features were similar to those of a synovial cyst, but synovium was not identified histologically. The imaging and pathologic features were unusual, including hemorrhage and a fibrohistiocytic reaction with giant cells.