Chondroblastoma of the femoral neck as a cause of hip synovitis.

Chondroblastoma is a rare benign chondroid bone tumor, which typically arises from the epiphysis of a long tubular bone. We present a 13-year-old girl with persistent hip synovitis caused by a chondroblastoma that arose from the femoral neck (metaphysis) and uniquely extended extraosseously into the hip joint. Computed tomography scan clearly demonstrated a tumoral lesion of the left femoral neck and a periosteal reaction along the anterior cortex of the femur, distal to the legion. Magnetic resonance imaging showed reactive synovitis with marked joint effusion of the hip and an extensive edema in the proximal femur and the surrounding soft tissues. Aneurysmal bone cysts formation secondary to chondroblastoma was confirmed by histologic examinations of the excised specimens. Complete relief of pain and an improvement in the range of movement of the hip joint was obtained after surgical resection of the tumor.