Bizarre parosteal osteochondromatous proliferation: a review of seven cases

Background: Bizarre parosteal osteochondromatous proliferation (BPOP) is a rare tumour-like condition mostly affecting the tubular bones of the hands and feet. Although it recurs in 50% of cases after local excision, it is a form of heterotopic ossification and its behaviour is otherwise benign. The present study describes seven cases of BPOP collected by the Bone Tumour Registry of New South Wales.
Methods: Clinical data, radiographs and histological specimens collected by the Bone Tumour Registry of New South Wales were examined, and further clinical data were sought from the referring doctor where necessary. Results: Six males and one female aged 18 to 37 years (median 30 years) presented between 1988 and 1995. There were three cases involving the hands, three involving the feet and one involving the distal humerus. Initial treatment was by local excision in all cases. There was local recurrence in three cases. The initial diagnosis was wrong in five of the seven cases. Radiologically, BPOP appears as a well-defined tumour arising directly from the bony cortex, without periosteal reaction or change to the underlying bone. Histologically, a large amount of hypercellular cartilage shows maturation to trabecular bone, which frequently contains spindle cells in the intertrabecular spaces. Conclusion: BPOP is a rare, locally recurrent but otherwise benign condition of bone which must be distinguished from more sinister lesions such as parosteal osteosarcoma and chondrosarcoma.