Enchondroma protuberans masquerading as osteochondroma.

Two cases of enchondroma protuberans are presented. The term enchondroma protuberans is designed to indicate a previously unrecognized and probably rare entity occurring in a long bone in an exaggeratedly eccentric fashion and, radiographically, remarkably resembling an osteochondroma. However, the morphologic differences between these two lesions are quite obvious and are easily demonstrable. Two young male patients, 10 and 15 years of age, had essentially similar lesions that developed, coincidentally, in the upper end of the left humerus. Improper radiographic interpretation of the lesions in both cases resulted in unnecessary second operations.