Introduction
When evaluating an aggressive bone lesion, radiologists often face a diagnostic challenge: Osteosarcoma, Ewing sarcoma, or Metastasis?
These entities can appear similar but have distinct imaging clues that guide diagnosis, biopsy, and management.
Imaging Features
1. Osteosarcoma
- Age: Adolescents & young adults (10–25 years).
- Location: Metaphysis of long bones (distal femur, proximal tibia, proximal humerus).
- X-Ray:
- Mixed lytic-sclerotic lesion.
- Aggressive periosteal reaction (sunburst, Codman triangle).
- Cortical destruction, soft tissue extension with ossified matrix.
- CT/MRI:
- Shows mineralized osteoid within soft tissue mass.
- MRI for marrow & neurovascular invasion.
2. Ewing Sarcoma
- Age: Children & adolescents (5–20 years).
- Location: Diaphysis of long bones, pelvis, ribs.
- X-Ray:
- Permeative lytic lesion.
- Onion-skin (lamellated) periosteal reaction.
- Large soft tissue mass, usually without calcification.
- CT/MRI:
- MRI: soft tissue component > intraosseous changes.
- CT: bone destruction, cortical breach.
3. Bone Metastasis
- Age: >40 years (unless known primary earlier).
- Location: Axial skeleton (spine, pelvis, ribs), proximal femur & humerus.
- X-Ray:
- Lytic, sclerotic, or mixed lesions depending on primary (e.g., breast – sclerotic, lung/renal – lytic, prostate – sclerotic).
- No characteristic periosteal reaction (usually minimal).
- CT/MRI:
- CT: defines cortical destruction.
- MRI: marrow replacement, multiple lesions.
- Nuclear medicine (Bone scan, PET-CT): detect multifocality.
📝 Comparison Table
| Feature | Osteosarcoma | Ewing Sarcoma | Metastasis |
|---|---|---|---|
| Age group | 10–25 yrs | 5–20 yrs | >40 yrs (unless known malignancy) |
| Common site | Metaphysis (femur, tibia, humerus) | Diaphysis (long bones, pelvis, ribs) | Axial skeleton, proximal long bones |
| X-ray appearance | Mixed lytic-sclerotic, sunburst, Codman triangle | Permeative lysis, onion-skin periosteal reaction | Lytic/sclerotic/mixed, non-specific |
| Soft tissue mass | Ossified matrix within mass | Large, often non-calcified | Variable, depends on primary |
| Periosteal reaction | Sunburst, Codman triangle | Onion-skin | Usually absent/minimal |
| Special notes | Mineralized osteoid production | Small round blue cell tumor | Consider primary malignancy |
Key Teaching Points
- Osteosarcoma → metaphyseal, ossified soft tissue mass, sunburst reaction.
- Ewing sarcoma → diaphyseal, onion-skin reaction, large soft tissue mass.
- Metastasis → older patients, axial skeleton, variable appearance.
Conclusion
Distinguishing between osteosarcoma, Ewing sarcoma, and metastasis requires correlating age, location, and imaging features. A structured approach helps narrow the differential and guides appropriate biopsy and treatment planning.
