Magnetic resonance imaging characteristics of bizarre parosteal osteochondromatous proliferation of the hand: a case report.

Bizarre parosteal osteochondromatous proliferation (BPOP) is a reactive lesion of cortical bone. A case of fifth metacarpal BPOP with intramedullary inflammatory extension is shown by magnetic resonance imaging. Histologically the intramedullary extension showed fibrosis with inflammatory cell infiltration. The surrounding adipose tissue showed fibrosis, focal inflammatory cell infiltration, and vascular proliferation. It is important to recognize that BPOP can bear radiologic resemblance to malignant lesions or osteomyelitis when there is an intramedullary inflammatory extension. Preservation of cortical bone under the osteocartilaginous mass on T1-weighted magnetic resonance imaging, and homogenous intramedullary enhancement with gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA), can be helpful for distinguishing BPOP from malignant lesions.