Periosteal chondrosarcoma in a 9-year-old girl with osteochondromatosis

A 9-year-old girl with multiple osteochondromatosis presented with a 1 year history of a gradually enlarging surface lesion originating from the midsection of the right humerus, distal to an osteochondroma. Radiographically and histologically this lesion proved to be a periosteal chondrosarcoma adjacent to an osteochondroma.