Osteochondroma
Overview
- Most common benign bone tumor
- Composed of bony outgrowth (Exostosis) covered by cartilage cap
- Always has continuity of cortex and medullary cavity with the parent bone
- Occurs at the metaphysis, grows away from the joint
- Can be solitary or part of Multiple hereditary exostoses (MHE)
Epidemiology
- Age: Typically arises in childhood/adolescence
- Stops growing after skeletal maturity
- Male > Female
- Multiple lesions → think MHE (autosomal dominant)
Common Locations
- Metaphysis of long bones, especially around the knee:
- Distal femur
- Proximal tibia
- Also seen in:
- Humerus, scapula, pelvis
- Rare in small bones
Complications
- Neurovascular impingement (esp. near popliteal artery)
- Fracture at stalk (pedunculated)
- Bursitis overlying the lesion
- Malignant transformation (to secondary Chondrosarcoma):
- Rare (<1% in solitary lesions, ~5% in MHE)
- Suspect if:
- New pain/swelling in adult
- Cap thickness >2 cm
- Cortical irregularity or soft tissue mass
Imaging Features
X-ray / CT
- Exophytic lesion projecting away from nearby joint
- Continuous cortex and medullary canal with parent bone
- Sessile or pedunculated base
- Cartilage cap often not visible on radiograph
- No aggressive features (unless malignant transformation)
MRI
- Best for evaluating:
- Cartilage cap thickness
- Neurovascular impingement
- Bursa formation or fracture - Cartilage cap: T2 bright
- Adults: <1.5–2 cm = benign
- >2 cm → suspicious for secondary chondrosarcoma
Differential diagnosis
All of these lack cortex and medullary continuity with the parent bone.
| Diagnosis | Key Differences |
|---|---|
| Parosteal osteosarcoma | Attached to cortex but no medullary continuity; often metaphyseal |
| Osteoma | Dense, ivory-like, craniofacial bones only |
| Periosteal chondroma | Juxtacortical, but scallops cortex and lacks medullary continuity |
| Nora’s lesion (BPOP) | Exophytic but no medullary continuity, more irregular and recurrent |
| Trevor disease (Dysplasia epiphysealis hemimelica) |
- Epiphyseal osteochondroma-like cartilage tumor - Growing from epiphysis toward the joint; usually ankle/knee |
Management
- No treatment needed if asymptomatic and benign-appearing
- Surgical excision if:
- Painful
- Causing mechanical symptoms or neurovascular compression
- Suspicious for malignant transformation
- Lifelong monitoring in MHE due to transformation risk
Exam tips
- Buzzword: "Cortex and medullary continuity"
- Cartilage cap >2 cm = red flag in adults
- Most common benign tumor; often incidental finding
- Know difference between pedunculated (height > base) and sessile (flat base) types
- MHE = multiple, bilateral, symmetrical lesions
