Chondroblastoma
The most common chondroid tumor at the epiphysis, especially in skeletally immature patients.
Epidemiology:
- Rare overall, but relatively common among epiphyseal lesions
- Age: 10–25 years
- Male > Female (2–3:1)
Common Locations
- Epiphysis or apophysis of long bones:
- Proximal tibia
- Proximal femur
- Proximal humerus
- Distal femur
- Less common: Talus, calcaneus, pelvis
Histology
- Chicken-wire calcification: thin, lace-like calcification around tumor cells
- Polygonal chondroblasts with grooved nuclei
- Multinucleated giant cells may be present
- Immunohistochemistry: S100 positive, DOG1 negative
Radiological Features
Radiograph / CT
- Eccentric epiphyseal lytic lesion
- Well-defined margin with sclerotic rim
- May show chondroid matrix calcification (stippled or flocculent)
- Possible growth plate disruption or epiphyseal expansion
MRI
- T1: Low to intermediate signal
- T2: Variable; often low to intermediate due to calcification or cellularity
- Surrounding bone marrow and soft tissue edema is common
- May show fluid-fluid levels if secondary Aneurysmal bone cyst (ABC) present
Differential diagnosis
| Diagnosis | Key Differences |
|---|---|
| Giant cell tumour |
- Older age group (20–40, skeletally mature) - Extends from metaphysis to epiphysis, lacks matrix calcification |
| ABC (secondary) | - Fluid-fluid levels dominant - Younger age - Metaphyseal location more typical |
| Clear cell chondrosarcoma | - Older patients, similar location - More aggressive, cortical breakthrough more likely |
| Brodie's abscess | - Clinical signs of infection - Serpiginous border, sequestrum possible |
| Pediatric osteomyelitis | - Systemic signs - Metaphyseal or epiphyseal lucency, ill-defined margins |
Management
- Surgical curettage with or without bone grafting
- Local recurrence in 10–15% of cases
- Rare benign pulmonary metastases (histologically benign but spreads)
- Follow-up imaging recommended due to recurrence potential
Exam tips
- Classic exam case: adolescent male with epiphyseal lesion containing chondroid matrix
- Rare but testable sites: talus, pelvis
- Histology buzzword: chicken-wire calcification
- Key differentiators: patient age, lesion location, matrix presence
Real-Life Practice Considerations
- Age and location are strong diagnostic clues
- Always assess:
- Epiphyseal involvement and proximity to growth plate
- Presence of edema or fluid-fluid levels (ABC component)
- If imaging is atypical or lesion is in an unusual location, recommend biopsy
- Mention recurrence risk and rare possibility of pulmonary spread
