(27) Bizarre Parosteal Osteochondromatous Proliferation: A Premalignant Process?

Abstract: First described by Nora et al. in 1983, the Bizarre Parosteal Osteochondromatous Proliferation (BPOP) was primarily reported in the bones of the hands and feet. The lesion is often confused with other benign and malignant lesions. Rarely reported in the maxillofacial region, few cases have been reported in the literature to date. Its etiology is unknown and it has a marked propensity to recur. The objective of this presentation is to present two unique cases, review management philosophies and bring attention to difficulties in accurately diagnosing this entity.

PubMed was searched for English language articles related to BPOP or Nora’s lesion as it is otherwise known. The articles were reviewed as well as relevant references to gather all cases of this lesion reported in the maxillofacial region. Two recent cases encountered at our institution are presented.

BPOP was first presented by Nora et al. in 1983 with a report of 35 lesions primarily involving the hands. Meneses et al. reported the first case in the head and neck in 1993 within a 65 case series. Since that time, cases in the mandible, maxilla, zygoma, and nasal bones have been reported. Currently, a total of 8 cases have been reported in the maxillofacial region. We present 2 additional cases from our institution. The first case is of an 11-year-old male who presented for evaluation of a growing, non-painful lesion under his left eye. Our exam revealed a palpable 1x1 cm bony lesion below the left infra-orbital rim. Imaging revealed a well-circumscribed, exophytic lesion extending from the cortical bone. The lesion was excised and histopathological evaluation yielded a rare diagnosis of BPOP. The patient has been followed for 2 years without signs of recurrence. The second case is of a 43-year-old male who presented with an anterior maxilla lesion. This lesion was biopsied twice and resected and histopathological evaluation was consistent with BPOP in all cases. The lesion ultimately recurred with the complete resection specimen demonstrating osteosarcoma.

BPOP is a rare entity with a high potential for recurrence. The lesion presents radiographically as a well-defined, broad-based calcific mass attached to the underlying cortical bone. Histologically the lesions resemble osteochondroma or osteosarcoma; however, these can be distinguished with adequate biopsy samples. There are some key features that can assist in distinguishing BPOP lesions from other osseous lesions. Radiographically, there is little to no alteration of the underlying cortical bone. Histologically, numerous chondrocytes with bizarre enlarged binucleated cells and hyperchromatic nuclei are typically present without significant atypia. There will also be the presence of “blue bone” characterized by deep blue H&E staining of the immature trabeculae and a hypercellular cartilage cap. The consensus among current literature is that BPOP lesions should be removed in entirety without wide margins. We present two novel cases, one in which multiple biopsies indicated a lesion to be a BPOP but ultimately proved to be an osteosarcoma, bearing significant consequences for the patient. Whether this is a spectrum of malignant progression is unclear. We as oral and maxillofacial surgeons need to be aware of this possibility. The paucity of documented cases make it difficult to determine whether this is in fact a premalignant process of developing osteosarcoma and what the most appropriate management should be.

1. FE Nora et al. Bizarre parosteal osteochondromatous proliferations of the hands and feet. Am J Surg Pathol. Apr;7(3):245-50. 1983.
2. MF Meneses et al. Bizarre parosteal osteochondromatous proliferation of bone (Nora's lesion). Am J Surg Pathol. Jul;17(7):691-7. 1993.