Chondrosarcoma arising within synovial chondromatosis of the lumbar spine.

Synovial chondromatosis is an uncommon benign neoplasm that usually affects large appendicular joints and only rarely the spine. There are only a few small series and case reports documenting malignant transformation of synovial chondromatosis into secondary chondrosarcoma, typically within the hip in the setting of recalcitrant disease and multiple recurrences. Chondrosarcoma arising in synovial chondromatosis of the spine is exceedingly rare, with only one previously published case report involving the craniocervical junction. We present a case of chondrosarcoma arising within synovial chondromatosis of the lumbosacral spine, with the diagnosis made at the time of initial presentation. We describe the clinical, imaging, and histopathological findings and review diagnostic criteria for this difficult diagnosis.