Bizarre Parosteal Osteochondromatous Proliferation
Synonyms: BPOP, Nora lesion
Rare reactive/neoplastic lesion of bone surface
Quick Facts
Behaviour
Benign
Category
Bone
Synonyms
- BPOP
- Nora lesion
Category
Bone
Behaviour
Benign
Gender
M = F
Tissue of Origin
Bone
Epidemiology
- Wide age range, peak 3rd–4th decade
- Often associated with prior trauma
Clinical Features
- Painful swelling on bone surface
- Rapid growth may raise concern for malignancy
Location
- Small bones of hands and feet most common
- Distal phalanges of fingers
- Rarely long bones or skull
Imaging
- Pedunculated or sessile surface lesion
- Mineralised matrix (calcified cartilage and bone)
- No cortical destruction
- CT shows dense mineralisation arising from cortical surface
Pathology
- Bizarre Cartilage with hypercellularity and nuclear atypia
- Mineralising Fibrous tissue
- 'Blue' Cartilage (basophilic myxoid matrix)
- No continuity with medullary canal (unlike osteochondroma)
Genetics
- t(1;17)(q32-42;q21-23) translocation reported in some cases
- COL6A3-USP6 fusion described
- Uncertain whether neoplastic or reactive
Treatment
- Local excision - marginal or intralesional
- High recurrence rate (50–55%) - multiple excisions may be required
- No malignant transformation reported
Prognosis
- Benign but locally aggressive with high recurrence rate
- No metastatic potential
- Repeated excisions may be needed
Key Points
- Rare reactive/neoplastic lesion of bone surface
- Cytological atypia mimics malignancy but behaviour is benign
- Lack of medullary continuity distinguishes from osteochondroma
- Recurrence in >50% after simple excision
Workup - Blood Tests
No blood tests required
Workup - Local Imaging
- Plain radiograph - mineralised surface lesion; no medullary continuity
- CT- characterises mineralisation, confirms no cortical destruction
- MRI - if soft tissue extension or malignancy suspected
Workup - Biopsy
Excision biopsy preferred - complete removal diagnostic and therapeutic
Workup - Staging
No staging required
Workup - Other
MDT discussion if imaging ambiguous - exclude parosteal osteosarcoma before excision
Follow-up Summary
Patient education
advise that multiple local excisions may be necessary
High recurrence rate after excision; active surveillance required
Medical disclaimer
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