Ewing sarcoma
Overview
- High grade malignant small round blue cell tumour of bone and soft tissue
- Second most common primary bone malignancy in children and adolescents (after osteosarcoma)
- Characterized by t(11;22)(q24;q12) → EWSR1–FLI1 (most common).
- Age: Most commonly affects children and adolescents, typically 10–20 years
- Slight male predominance
- Painful mass is common; may have systemic features (fever, anemia, leukocytosis)
Common Locations
- Diaphysis or metadiaphysis of long bones
- Femur, tibia, humerus
- Also affects pelvis, ribs, and flat bones
- Can originate in soft tissue (extraskeletal Ewing sarcoma)
Imaging Features
Disproportionately large soft-tissue mass compared with the amount of cortical destruction
X-ray / CT
- Aggressive permeative or moth-eaten lytic lesion
- Poorly defined margins
- Classic lamellated periosteal reaction (onion-skin appearance)
- May also see:
- Codman's triangle
- Sunburst pattern (less common)
- Often with soft tissue mass
- No matrix mineralization
- Bone expansion uncommon
MRI
- T1: Low to intermediate signal
- T2/STIR: High signal in tumor and soft tissue mass
- Post-contrast: Enhances diffusely
- MRI is essential for local staging:
- Intramedullary extent
- Soft tissue involvement
- Neurovascular encasement
Differential Diagnosis
| Diagnosis | Key Differences |
|---|---|
| Osteomyelitis | - Abscess/cloaca/sinus tract, sequestrum - Clinical course / response to antibiotics |
| Lymphoma of bone | - Older age group - Less florid periosteal reaction - Large marrow component with relatively preserved cortex |
| Metastasis (e.g. neuroblastoma) | - Younger child (often <5 yo), multifocal lesions - History of primary tumor |
| Osteosarcoma | Osteoid matrix, metaphyseal location, sunburst periosteal reaction |
| Small-cell osteosarcoma | Similar histology, but produces osteoid; need biopsy and IHC to distinguish |
Management
- Neoadjuvant chemotherapy → surgical resection → adjuvant chemotherapy ± radiotherapy
- Multimodal treatment is standard
- Radiotherapy may be used for:
- Inoperable tumors (e.g. spine, pelvis)
- Positive margins or poor chemo response
Prognosis
- 5-year su rvival:
- 70–80% for localized disease
- <30% if metastatic at presentation
- Poor prognostic factors:
- Metastases (especially to lung or bone)
- Pelvic site → can look more sclerotic/mixed and can be bulky at presentation
- Large tumor volume
- Poor response to chemotherapy
Staging Workup
- MRI of local site
- Chest CT (lung metastasis).
- Bone scan or FDG-PET/CT (metastatic survey).
- Bone marrow biopsy: may be performed (protocol-dependent), especially if concern for marrow disease.
Exam Tips
- Classic stem: 10–20y with deep bone pain ± fever, diaphyseal/metadiaphyseal long-bone (or pelvis/rib) lesion + large soft-tissue mass.
- Radiograph buzz: permeative/moth-eaten lysis, wide zone of transition, lamellated (“onion-skin”) periosteal reaction ± Codman triangle; no osteoid/chondroid matrix.
- Path confirm line: t(11;22) → EWSR1–FLI1; IHC typically diffuse membranous CD99+ (supportive, not specific).
- Curveball: extraskeletal Ewing = soft-tissue mass in a teen with the same fusion; treat as Ewing family tumour, not a random sarcoma.
