Bizarre parosteal osteochondromatous proliferation

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 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 BPOP, although radiographic features alone cannot reliably diagnose the lesion.

They are benign lesions with no risk of distant metastasis but they may show marked local invasion and may recur after surgical excision.

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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Article information

rID: 995
Synonyms or Alternate Spellings:
  • Nora lesion
  • Nora lesions
  • Bizarre parosteal osteochondromatous proliferation (BPOP)

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