Chondroblastoma patella

This is a case of a 17 year old woman who presents with anterior knee pain and swelling. Frontal radiograph of the knee demonstrates a subtle lytic lesion in the patella. The second image is a lateral radiograph which better depicts the mass. The lesion is slightly expansile and is well circumscribed. No matrix is appreciated radiographically. There is no evidence of a pathologic fracture, perisoteal reaction, or a soft tissue component to suggest that this is an agressive osseous lesion. The patella, which is the largest sesamoid bone in the body, is considered an epiphyseal equivalent in terms of histology of tumors that occur with the bone. Given the patients age, radiographic appearance, and location, findings are most suggestive of a chondroblastoma. Chondroblastomas may or may not show a chondroid matrix on radiographs due to their varying composition of hyaline cartilage or fibrocartilage.