Bizarre parosteal osteochondromatous proliferation of the ulna

Bizarre parosteal osteochondromatous proliferation of bone (BPOP) is a rare, benign lesion consisting of bone, cartilage and fibrous tissue, which most commonly arises in the hands and feet of young adults. When arising in atypical locations such as long bones, this entity can present a diagnostic challenge to radiologists. We report a case of BPOP arising from the ulna that mimicked an osteochondroma radiologically, and describe the radiographic, CT and MR appearances of this lesion.