Bizarre parosteal osteochondromatous proliferation with cortical invasion.

A 15-year-old male presented with an 18-month history of increasing swelling on the radial aspect of his left forearm. Radiographs and MR images showed a partly calcified mass on the lateral border of the radius with erosion of the underlying cortex. Following a CT-guided needle biopsy, the mass was excised by segmental resection of the radial shaft with replacement by a vascularised fibular graft. Histological examination of the resected specimen showed many features typical of a bizarre parosteal osteochondromatous proliferation (BPOP) but with destruction of the underlying cortical bone by cellular spindle cell tissue. Although there were no cytological signs of malignancy, we believe that this unusual disease should be regarded as a particularly aggressive form of BPOP and treated by wide excision. Clinical follow-up of our patient at 2 years shows no sign of local recurrence or metastasis.