Fig. 4

Osteoid osteoma mimicking synovitis of the hip. A 24-year-old man with right hip pain, swelling and tenderness for 2 weeks. Inflammatory marker levels were also elevated. Orthopedists suspected inflammatory arthropathy, and ultrasound (not shown) depicted joint effusion and synovitis. MRI T2 FS sagittal (a) and axial (b) shows joint effusion (arrowhead) with synovial thickening and a doubtful nidus (arrow), which was better characterized on the CT scan (c). Arthroscopic aspect before (d) and after (e) nidus resection