Figure 1. Images of the patient discussed in case one.

Initial weight-bearing AP (A) and lateral radiographs (B) were unremarkable. The osteoid osteoma lesion is better delineated on the MRI; sagittal inversion recovery (C), axial proton density (D), and sagittal proton density (E) images are shown. The lesion was also seen on the weight-bearing axial CT (F). Intra-procedure CT images demonstrate successful targeting of the lesion with RFA (G, H).

MRI: magnetic resonance imaging; CT: computed tomography; RFA: radio-frequency ablation