Bizarre parosteal osteochondromatous proliferation (BPOP) is a benign lesion of bone originally described by Nora et al in 1983. To date there are no UK-based case series in the literature. Here we present the Scottish Bone Tumour Registry (SBTR) experience of this rare lesion.

A retrospective analysis of SBTR records was performed. Histological specimens were re-examined by a consultant musculoskeletal oncology pathologist. Radiographs were re-reported by a consultant musculoskeletal radiologist. From 1983-2009, 13 cases were identified; 6 male, 7 female. Age ranged from 13-65. All patients presented with localised swelling. Pain was present in 5 and trauma in 2. 9 lesions affected the hand, 3 the foot, and 1 the tibial tuberosity. 12 lesions were excised and 1 curetted. There were 7 recurrences of which 6 were excised. 1 patients' recurrence was not treated. 1 lesion recurred a second time. This was excised. There were no metastases. Radiographs typically showed densely mineralised lesions contiguous with an uninvolved cortex. Cortical breakthrough was present in 1 case and scalloping in another. Histology characteristically showed hypercellular cartilage with pleomorphism and calcification/ossification without atypia; bone undergoing maturation; and a spindle-cell stroma.

SBTR records indicate that BPOP is a rare lesion with no sex predilection that affects patients over a wide age range. Minor antecedent trauma was present in only 2 cases. In agreement with Nora et al. we feel that trauma is unlikely to represent an aetiological factor. Recurrence was over 50% in this series. Although this is similar to that found in other reports, it may indicate that more extensive resection is required for this aggressive lesion. Finally, although radiological/histological findings are often bizarre there have been no reported metastases and so it is important that BPOP is not mistaken for, or treated as, a malignant process such as chondrosarcoma.