Bizarre parosteal osteochondromatous proliferation

Bizarre parosteal osteochondromatous proliferation (BPOP) (also known as a Nora lesion) is a benign exophytic osteochondral lesion which has an appearance similar to an osteochondroma, and is typically seen in the hands and feet. 

BPOPs are 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 recognised gender predilection.

Plain radiograph

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.  

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

Imaging differential considerations include:

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Article Information

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

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