Osteoid osteoma mimicking Brodie's abscess in a 13-year-old girl.

Osteoid osteoma is a solitary, benign lesion of bone causing significant nocturnal pain. Magnetic resonance imaging (MRI), computed tomography (CT), and bone scan are commonly used in this diagnosis. A case of osteoid osteoma of the distal femur mimicking chronic osteomyelitis with Brodie's abscess is reported and discussed. Initial radiographs and MRI showed a lesion of the distal femur consistent with subacute osteomyelitis with a Brodie's abscess. Because primary malignant tumor could not be eliminated, surgical biopsy was carried out. Histological examination showed a typical nidus consistent with the diagnosis of osteoid osteoma. Subacute osteomyelitis (Brodie's abscess) may be difficult to distinguish from other malignant or benign bone lesions as osteoid osteoma. CT usually is recommended as the best imaging procedure to identify the nidus and confirm the diagnosis. MRI also can be used for this purpose. Surgical biopsy remains mandatory for unclear lesions before deciding on appropriate treatment.