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Disease Profile

Bizarre parosteal osteochondromatous proliferation

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


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Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

BPOP; Nora lesion; Nora’s Lesion


Connective tissue diseases


Bizarre Parosteal Osteochondromatous Proliferation (BPOP), also known as Nora’s lesion, is an uncommon, benign bone tumor that grows on the surface of the bone. In some cases, BPOP does not cause symptoms. However, at other times, it can be painful and lead to bone deformity.[1][2] It is more commonly located on the hands and feet, but can also affect the long bones or bones of the skull and face. A biopsy of the affected bone is important, as BPOP may resemble malignant bone tumors, especially chondrosarcoma or parosteal osteosarcoma.[3] The cause is still unknown though injuries or bone defects may trigger the condition in some cases. Treatment involves surgery to remove the tumor. There is a 20%-50% chance that the condition may reappear after surgery.[2][3]

Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

In-Depth Information

  • PubMed is a searchable database of medical literature and lists journal articles that discuss Bizarre parosteal osteochondromatous proliferation. Click on the link to view a sample search on this topic.


  1. Kershen LM, Schucany WG & Gilbert NF. Nora’s lesion: bizarre parosteal osteochondromatous proliferation of the tibia. Proceedings (Baylor University Medical Center). 2012; 25(4):369-371. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3448582/.
  2. Hussain MM, Arif KS. Bizarre Parosteal Osteochondromatous Proliferation causing angular deformities:. A Case Report. Journal of Orthopaedic Case Reports. 2015; 5(1):45-47. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4719352/.
  3. Mors M, Cervantes SS & Hinni M. Bizarre parosteal osteochondromatous proliferation presenting in the nasal dorsum. Journal of Oral and Maxillofacial Pathology?: JOMFP.. 2015; 19(1):109. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4451655/.