Usual clinical presentation of bizarre parosteal osteochondromatous proliferation (BPOP) with unusual histology.

Bizarre parosteal osteochondromatous proliferation (BPOP) or Nora's lesion is a unique, bony lesion that most often arises in the small bones of the hands and feet. The lesion was first described by Nora et al. in 1983, and documented cases have now shown the lesion to arise in the long bones, skull, maxilla and mandible. Radiographically, the bony lesion typically lacks a connection with the adjacent medullary cavity which is commonly seen with osteochondroma, the main differential diagnosis for Nora's lesion. Reported is the case of a 35-year-old male who presented to the orthopedic clinic after a non-painful mass arising on the right index finger was identified on routine physical examination. The lesion was surgically removed and sent for pathologic evaluation. Microscopic examination of the lesion revealed a disordered spindle cell proliferation and trabecular bone with no cartilaginous cap. The findings were believed to represent an osteocartilaginous neoplasm with radiographs and magnetic resonance imaging (MRI) suggestive of Nora's lesion. Thus, it was felt that the lesion fell within the overall spectrum of BPOP. The lesion is a unique entity that requires a complete history and physical exam along with radiographic and histologic analysis for proper identification. The lesion is benign but may be locally aggressive. Complete excision is the treatment of choice, and recurrence is common.