Osteoid osteoma. The double density sign.

Occasionally, osteoid osteoma can be difficult to radiographically differentiate from osteomyelitis. The precise localization of the nidus of an osteoid osteoma often can be difficult using nothing more than conventional radiographs. In a series of 35 patients, a radionuclide and double density sign facilitated localization of the nidus, confirmed the diagnosis, and aided the surgeon in excision biopsy. This series of cases demonstrates how computed tomography (CT) scanning can more precisely localize the nidus in areas deep in complex joints such as the hip. Fifteen cases of osteoid osteoma were studied with Tc-99m-MDP radionuclide bone scan. Each one exhibited the double density sign. Seven of these patients had CT scans in addition for further localization of the nidus. All were excised with accurate localization of the nidus, and thereby reduced morbidity and postoperative recovery time.