Solution: Osteoid osteomas are a benign skeletal neoplasm composed of osteoid and woven bone. Typical history is a young person with focal pain that is worse at night and with activity, but significantly relieved with even small doses of aspirin. They are classified as cortical, cancellous, or subperiosteal with cortical being the most common. They have no malignant potential. Several techniques are available for ablation of osteoid osteoma. The tumor can be percutaneously ablated by using radiofrequency (RF), ethanol, laser, or thermocoagulation therapy under CT guidance. They can also be resected, but this is less common. Note that in this case, the MRI might not be as clear as a CT might have been. Here are the CT images.