[Magnetic resonance tomography in osteoid osteoma: more confusion than benefit?]

The purpose of this evaluation was the description of potentially misleading MR appearances of osteoid osteoma. The MR images of 10 patients with osteoid osteoma were retrospectively evaluated and compared to radiographic, intraoperative and histologic findings. 4 of the 10 abnormalities were located in the proximal femur, two in the lumbar spine, and one each in the tibial plateau, in the cervical spine, in the sacrum and in the first metacarpal. 8 of the 9 nidi visible on standard radiographs and/or CT scans were demonstrated on MR images. Edema was visible within the bone marrow in 3, within soft tissue in 2 and in both locations in 4 MR examinations. The soft tissue abnormalities were circumscribed in 3 patients and could be misdiagnosed as soft tissue tumors or an abscess in these patients. One of 5 osteoid osteomas located in the proximity of a joint mimicked septic arthritis. The MR appearance of osteoid osteoma may be misleading. However, false diagnoses usually can be avoided with a careful search of a nidus. MR imaging in osteoid osteoma is important for differential diagnosis.