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

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Investigations Provided

Laboratory Results

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

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Questions & Model Answers

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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:

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

1. Don't treat as infection without biopsy - Ewing mimics osteomyelitis
2. Whole bone MRI - skip lesions change surgical planning
3. Biopsy tract planning - must be excised with tumour
4. Neoadjuvant chemotherapy first - don't proceed directly to surgery
5. MDT essential - sarcoma surgeon, oncologist, radiologist, pathologist
6. Histological response matters - >90% necrosis = good prognosis

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Common Examiner Follow-ups

Q: "What is the difference between 'onion skin' and 'sunburst' periosteal reaction?"

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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.

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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.

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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

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Related Topics

• Osteosarcoma
• Primary Bone Tumours
• Bone Tumour Staging (Enneking)
• Endoprosthetic Reconstruction
• Chemotherapy Protocols in Bone Sarcoma
• Rotationplasty