Osteoid osteoma. A lateral view (A) of the proximal tibia shows a very dense lesion in the posterior cortex. A darker central area contains a white nidus. This lesion in a 20-year-old man caused pain in this area, relieved by aspirin. B, A nuclear medicine bone scan in a different patient with an osteoid osteoma in the left lower tibia shows increased activity (arrows) at the site of the lesion.
Osteoid osteomas, especially those that arise beneath the periosteum, usually elicit a tremendous amount of reactive bone formation that encircles the lesion. The actual tumor, known as the nidus, manifests radiographically as a small round lucency that is variably mineralized
Specimen radiograph of intracortical osteoid osteoma. The round radiolucency with central mineralization represents the lesion and is surrounded by abundant reactive bone that has massively thickened the cortex.
Osteoid osteomas’ are considered benign and are normally treated by conservative surgery. However there is a possibility of malignant transformation. This is rare except when treated with radiation, which promotes this complication.