Osteochondroma: Causes, Genetics, and Malignant Transformation Risk

Osteochondromas are cartilage-capped bony projections (exostoses) arising from the growth plate periphery. Pathogenesis:

• Sporadic (80%): Solitary lesion; no family history. Somatic EXT1/EXT2 mutations in perichondrial cells.
• Hereditary Multiple Exostoses (HME): Autosomal dominant; germline EXT1 (60%) or EXT2 (30%) mutations → impaired heparan sulfate synthesis → dysregulated chondrocyte proliferation. Multiple lesions, often metaphyseal.
• Secondary: Associated with Ollier disease (enchondromatosis) or Maffucci syndrome (enchondromas + hemangiomas).

Malignant Transformation: HME carries 1–5% lifetime risk of chondrosarcoma (vs. <1% solitary). Risk factors: pelvic/scapular lesions, cartilage cap >1.5–2 cm in adults, rapid growth, pain.

Surveillance: Annual clinical exam; MRI if cap thickness or symptoms change. Resection indicated for symptomatic lesions or suspected malignancy.