Unusual presentation of osteoid osteoma mimicking osteomyelitis in a 27-month-old infant.

Osteoid osteoma is an uncommon, benign disorder of bone that is most often encountered in school-age children and in adolescents. It is quite rare in children under the age of 3 years. We report a case of osteoid osteoma with unusual clinical and imaging features in a 27-month-old toddler who presented with a limp and swelling of the right knee. Initial clinical evaluation, plain films, and computed tomography (CT) were strongly suggestive of chronic osteomyelitis involving the distal right femoral metadiaphysis. The appearance on nuclear medicine bone scan, however, was typical of osteoid osteoma. A biopsy of the lesion was taken and histological examination confirmed the diagnosis of osteoid osteoma. The misleading clinical and imaging features in this case are discussed.