Bizarre parosteal osteochondromatous proliferations (BPOP), also known as a 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 well a 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 mineralising 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 BPOP, although radiographic features alone cannot reliably diagnose the lesion.
Treatment and prognosis
They 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 is an American pathologist who first described the condition at Mayo Clinic in 1983 7.
Possible imaging differential considerations include:
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- 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. J Foot Ankle Surg. 2017 May - Jun;56(3):670-673. doi: 10.1053/j.jfas.2017.01.028. PMID:28268143
- 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