Synovial chondromatosis in a lumbar apophyseal joint.

A 31-year-old woman presented with painful swelling in the right paravertebral region that had been present for 2 years. Radiography and CT revealed an area of increased density due to multiple calcifications localized at the fourth lumbar vertebra. Histological examination revealed that the lesion consisted of nodules of hyaline cartilage, with focal areas of calcification, growing within synovial tissue.