(a)–(d) A 23-year-old boy with femur osteoid osteoma. (a) Preoperative radiograph showing osteosclerosis in the intertrochanter of the femur. (b) At 1 month after the first surgical operation, the bone marrow and soft tissue edema were still observed by MR T2WI with fat suppression. (c) At 2 weeks after the second surgical operation, MR T2WI with fat suppression demonstrated that the bone marrow and soft tissue edema disappeared. (d) The pathological slice of the specimen after second operation showed that the loose fibro-vascular mesenchyma between the trabeculae consisted of osteoid tissue or woven bone (HE × 200).