Bizarre parosteal osteochondromatous proliferations (BPOP), also known as Nora lesions, are benign exophytic osteochondral lesions which have an appearance similar to an osteochondroma and are typically seen in the hands and feet. On imaging, BPOPs are shown to be continuous with the underlying cortex, but usually without continuation of the medulla.
They are most often seen in young (20-30-year-old) patients. There is no recognized gender predilection.
Typically seen as a well-marginated wide-based bony growth projecting into the soft tissues although often lacks the characteristic orientation away from the nearby physis seen with osteochondromas. The mineralizing exophytic lesion arises from the cortical bone with or without osteolysis, cortical flaring or a periosteal reaction. A lack of medullary involvement is characteristic of bizarre parosteal osteochondromatous proliferation, although radiographic features alone cannot reliably diagnose the lesion.
Treatment and prognosis
Bizarre parosteal osteochondromatous proliferations are benign lesions with no risk of distant metastasis but they may show marked local invasion and may recur after surgical excision.
History and etymology
Frederick E Nora (fl. 2020) is an American pathologist who first described bizarre parosteal osteochondromatous proliferations whilst working at the Mayo Clinic in 1983 7.
Possible imaging differential considerations include:
- 1. Oviedo A, Simmons T, Benya E et-al. Bizarre parosteal osteochondromatous proliferation: case report and review of the literature. Pediatr. Dev. Pathol. 2002;4 (5): 496-500. Pubmed citation
- 2. deLange EE, Pope TL, Fechner RE et-al. Bizarre parosteal osteochondromatous proliferation vs. benign florid reactive periostitis. AJR Am J Roentgenol. 1987;148 (3): 650. doi:10.2214/ajr.148.3.650-a - Pubmed citation
- 3. Bush JB, Reith JD, Meyer MS. Bizarre parosteal osteochondromatous proliferation of the proximal humerus: case report. Skeletal Radiol. 2007;36 (6): 535-40. doi:10.1007/s00256-006-0236-8 - Pubmed citation
- 4. Teoh KH, Shortt N, Wilkinson G et-al. Bizarre parosteal osteochondromatous proliferation of the metatarsal: a pediatric case report and archival review. J Foot Ankle Surg. 2009;48 (6): 690.e7-690.e11. doi:10.1053/j.jfas.2009.06.012 - Pubmed citation
- 5. Gursel E, Jarrahnejad P, Arneja JS et-al. Nora's lesion: Case report and literature review of a bizarre parosteal osteochondromatous proliferation of a small finger. Can J Plast Surg. 2011;16 (4): 232-5. Free text at pubmed - Pubmed citation
- 6. Rushing CJ, Rogers DE, Spinner SM, Gajzer DC. A Case Report of Heel Pain Mimicking Plantar Fasciitis and Osteosarcoma: A Unique Presentation of a Nora's Lesion. (2017) The Journal of foot and ankle surgery : official publication of the American College of Foot and Ankle Surgeons. 56 (3): 670-673. doi:10.1053/j.jfas.2017.01.028 - Pubmed
- 7. Nora FE, Dahlin DC, Beabout JW. Bizarre parosteal osteochondromatous proliferations of the hands and feet. (1983) The American journal of surgical pathology. 7 (3): 245-50. Pubmed
Related Radiopaedia articles
The differential diagnosis for bone tumors is dependent on the age of the patient, with a very different set of differentials for the pediatric patient.
- bone-forming tumors
- cartilage-forming tumors
- bizarre parosteal osteochondromatous proliferation (Nora lesion)
- chondromyxoid fibroma
- juxtacortical chondroma
- fibrous bone lesions
- bone marrow tumors
- other bone tumors or tumor-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumor of bone
- Gorham massive osteolysis
- haemophilic pseudotumor
- intradiploic epidermoid cyst
- intraosseous lipoma
- musculoskeletal angiosarcoma
- musculoskeletal hemangiopericytoma
- primary intraosseous hemangioma
- post-traumatic cystic bone lesion
- simple bone cyst
- impending fracture risk