Chondroblastoma

This was a 20-years old man who had severe knee pain. The plain radiograph (Fig. 1) showed a well-defined osteolytic lesion in the epiphysis with a sclerotic rim and a central matrix of increased density. No significant surrounding sclerosis was seen.

An epiphyseal lesion such as this most commonly is a chondroblastoma, which it turned out to be on excision. Though an osteoid osteoma may present in this manner, the epiphyseal location and the lack of other findings go against this diagnosis. Often, these lesions do not have a chondroid matrix and appear to be purely osteolytic.

You can also see the other examples in the humeral and femoral heads.