Bizarre parosteal osteochondromatous proliferation with an inversion of chromosome 7.

Bizarre parosteal osteochondromatous proliferation (BPOP) is a benign exophytic proliferative lesion that predominantly involves the small tubular bones of the hands and feet. Histologically BPOP is characterized by a heterogeneous mixture of cartilage, bone and fibrous tissue. Recently, a translocation between chromosomes 1 and 17, or its variant translocations, has been reported to be unique in BPOP. The case of a 59-year-old woman with BPOP in the middle phalanx of the ring finger with increasing mass is reported herein. Computed tomography and magnetic resonance imaging depicted the central part of the exophytic bone lesion as having continuity to the underlying bone marrow, which is considered to be the typical finding of osteochondroma, but not a common finding in BPOP. In addition, an inversion of chromosome 7 [inv (7)(q22q32)] was observed. Therefore, this case suggests that the translocation between chromosomes 1 and 17 reported in other cases may not be the only cause of BPOP.