Ewing's Sarcoma - Adolescent Femur
CIM Case: Ewing's Sarcoma - Adolescent Femur
Clinical Scenario
Patient: 14-year-old male Presentation: 6-week history of progressive right thigh pain and swelling, worse at night, associated with low-grade fevers and night sweats Relevant history: Previously fit and active, no prior bone problems, no trauma, no family history of malignancy, 3kg weight loss over 6 weeks, decreased appetite, fatigue Examination findings:
- Unwell-appearing adolescent, pale
- Temperature 37.8°C
- Palpable warm, tender mass over distal right thigh (8cm × 6cm)
- Firm, fixed to underlying bone
- Visible distension of superficial veins over mass
- Range of motion at knee limited by pain
- No knee effusion
- Neurovascularly intact distally
- No palpable lymphadenopathy
- Chest clear
Investigations Provided
Laboratory Results
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| Hb | 98 g/L | 130-160 g/L | ↓ Anaemia |
| WCC | 12.5 ×10⁹/L | 4-11 ×10⁹/L | ↑ Leucocytosis |
| Platelets | 485 ×10⁹/L | 150-400 ×10⁹/L | ↑ Reactive thrombocytosis |
| CRP | 65 mg/L | <5 mg/L | ↑ Elevated |
| ESR | 85 mm/hr | <15 mm/hr | ↑ Markedly elevated |
| LDH | 580 U/L | 120-250 U/L | ↑ Elevated (prognostic marker) |
| ALP | 245 U/L | 150-420 U/L | Normal (bone turnover) |
| Uric acid | 0.48 mmol/L | 0.15-0.45 mmol/L | ↑ Slightly elevated |
Imaging
Image 1: AP and Lateral Radiographs of Right Femur
Radiological features:
- Large permeative/moth-eaten lesion in femoral diaphysis
- "Onion skin" periosteal reaction (lamellated)
- Codman triangle at proximal margin
- Lytic destruction without matrix mineralisation
- No sclerotic rim (aggressive lesion)
- Soft tissue mass extending from bone
- Lesion extends approximately 12cm in longitudinal axis
Image 2: MRI Right Femur with Contrast
MRI findings:
- Large intramedullary tumour with extensive marrow replacement
- Low T1 signal, high T2 signal, heterogeneous enhancement
- Large extraosseous soft tissue mass (8 × 6 × 10 cm)
- Tumour extends into adjacent muscle compartments
- No skip lesions identified on whole bone imaging
- Neurovascular bundle displaced but not encased
- No knee joint involvement
Image 3: CT Chest
Findings:
- Two small pulmonary nodules (4mm and 6mm) in right lower lobe
- Concerning for pulmonary metastases
- No mediastinal lymphadenopathy
Questions & Model Answers
What is your differential diagnosis and most likely diagnosis?
Describe the characteristic features of Ewing sarcoma.
What is your staging workup for this patient?
What is the treatment algorithm for Ewing sarcoma?
This patient has pulmonary metastases. How does this affect management?
Compare Ewing sarcoma with osteosarcoma.
Key Teaching Points
Pattern Recognition
This pattern suggests Ewing Sarcoma:
- Adolescent (10-20 years) with bone pain and systemic symptoms
- Diaphyseal or metadiaphyseal location
- Permeative/moth-eaten destruction on X-ray
- "Onion skin" lamellated periosteal reaction
- Large soft tissue mass disproportionate to bone lesion
- Elevated LDH and inflammatory markers
Age-Based Differential for Round Cell Tumours:
| Age | Most Likely Round Cell Tumour |
|---|---|
| 0-5 years | Neuroblastoma metastasis, leukaemia |
| 5-10 years | Eosinophilic granuloma (LCH) |
| 10-25 years | Ewing sarcoma |
| 25-40 years | Lymphoma |
| >40 years | Myeloma, metastases |
Small Round Blue Cell Tumours (Differential):
- Ewing sarcoma (CD99+, t(11;22))
- Lymphoma (CD45+, CD20/CD3+)
- Neuroblastoma (NSE+, NB84+)
- Rhabdomyosarcoma (desmin+, myogenin+)
- Small cell osteosarcoma (SATB2+, osteoid)
Critical Management Points
- Don't treat as infection without biopsy - Ewing mimics osteomyelitis
- Whole bone MRI - skip lesions change surgical planning
- Biopsy tract planning - must be excised with tumour
- Neoadjuvant chemotherapy first - don't proceed directly to surgery
- MDT essential - sarcoma surgeon, oncologist, radiologist, pathologist
- Histological response matters - >90% necrosis = good prognosis
Common Examiner Follow-ups
Q: "What is the difference between 'onion skin' and 'sunburst' periosteal reaction?"
| Feature | Onion Skin | Sunburst |
|---|---|---|
| Appearance | Concentric lamellated layers | Radiating spicules |
| Mechanism | Slow, intermittent periosteal elevation | Rapid, continuous tumour growth |
| Classic tumour | Ewing sarcoma | Osteosarcoma |
| Implication | Moderately aggressive | Highly aggressive |
Q: "What is the role of radiotherapy in Ewing sarcoma?"
Radiotherapy indications:
- Unresectable tumours (pelvis, spine, skull base)
- Marginal surgical margins
- Poor histological response to chemotherapy
- Lung metastases (whole lung irradiation)
Dose: 45-55 Gy for definitive treatment, 40-45 Gy if combined with surgery
Key point: Unlike osteosarcoma, Ewing sarcoma IS radiosensitive. This makes radiotherapy a viable option for local control when surgery would cause unacceptable morbidity.
Q: "What is a skip lesion and why is it important?"
Skip lesion definition: Separate tumour deposit in the same bone, not contiguous with primary lesion.
- Occurs in 10-15% of Ewing sarcoma
- Must image ENTIRE bone with MRI
- Skip lesion = worse prognosis
- Surgical resection must include skip lesion
- May require whole bone resection or diaphyseal resection
Missing a skip lesion leads to local recurrence and treatment failure.
Q: "How would you counsel this patient and family about prognosis?"
For metastatic Ewing sarcoma (this patient):
- Honest discussion about seriousness of diagnosis
- 5-year survival approximately 20-30% with lung-only metastases
- Treatment is intensive (12+ months)
- Significant side effects (nausea, hair loss, infection risk)
- Fertility preservation discussion before starting chemotherapy
- Need for long-term surveillance even if cured
- Involvement of paediatric oncology nurse, psychologist, social worker
- Family support resources, youth cancer support groups
Related Topics
- Osteosarcoma
- Primary Bone Tumours
- Bone Tumour Staging (Enneking)
- Endoprosthetic Reconstruction
- Chemotherapy Protocols in Bone Sarcoma
- Rotationplasty