CIM Case: Osteosarcoma

Clinical Scenario

Patient: 15-year-old male Presentation: 2 months of increasing left thigh and knee pain, worse with prolonged activity, occasional knee effusions Relevant history: No trauma, previously active in school sports (now limited by pain), no constitutional symptoms, no family history of bone disease Examination findings:

• Antalgic gait favouring left leg
• Mild but notable increase in left thigh girth (2cm compared to contralateral side)
• Firm, tender mass palpable in distal left thigh
• Warmth present over mass, no erythema
• Moderate left knee effusion
• Full range of motion of knee preserved
• No distal neurovascular deficit

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Investigations Provided

Laboratory Results

Imaging

Image 1: AP and Lateral Radiograph of Left Distal Femur

Radiological features:

• Aggressive mixed lytic/blastic lesion in distal femoral metaphysis
• Ill-defined margins with permeative destruction
• Aggressive periosteal reaction: Codman triangle and sunburst pattern
• Cloud-like osteoid matrix mineralisation within the lesion
• Soft tissue extension with calcification
• No pathological fracture
• Knee joint not involved

Image 2: MRI Left Femur (Whole bone with joints above and below)

MRI findings:

• 8 × 6 × 10 cm mass centred in distal femoral metaphysis
• Heterogeneous signal with low T1 and mixed T2 signal
• Extensive soft tissue component with enhancement
• Neurovascular bundle displaced but not encased
• Skip lesion excluded (important staging feature)
• No intra-articular extension
• Proximal physis not involved

Image 3: CT Chest

Findings:

• Two small pulmonary nodules in right lower lobe (5mm and 7mm)
• Suspicious for pulmonary metastases

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Questions & Model Answers

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Key Teaching Points

Pattern Recognition

This pattern suggests Osteosarcoma:

• Adolescent with pain and swelling around knee
• Metaphyseal location in distal femur (most common site)
• Elevated ALP (marker of osteoid production)
• Radiographic: Sunburst periosteal reaction, Codman triangle, osteoid matrix

Distinguish from Ewing Sarcoma:

Distinguish from Osteomyelitis:

• Osteomyelitis: Fever, acutely unwell, elevated WCC/CRP
• Osteosarcoma: Indolent, no fever, ALP elevated rather than acute inflammatory markers
• Both can have periosteal reaction - imaging pattern differs

Critical Management Points

1. Refer to sarcoma centre - do not biopsy without discussion
2. MRI whole bone - exclude skip lesions
3. CT chest - pulmonary metastases
4. Biopsy by treating surgeon - technique affects outcome
5. Neoadjuvant chemotherapy before surgery - standard of care
6. Limb salvage in 80-90% - amputation rarely necessary
7. Metastases can be cured - aggressive treatment

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Common Examiner Follow-ups

Q: "What are skip lesions and why are they important?"

Skip lesions are separate foci of tumour in the same bone, discontinuous from the primary tumour. Important because:

• Occur in 3-5% of osteosarcomas
• Must be included in resection (contraindicate joint-sparing surgery)
• Require MRI of entire bone for detection
• Associated with worse prognosis

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Q: "What is a Codman triangle?"

A Codman triangle (Codman angle) is a triangular area of periosteal new bone formation at the margin of a bone tumour. It forms where the elevated periosteum meets the normal cortex. It indicates aggressive periosteal reaction but is NOT pathognomonic for malignancy (can occur in infection or trauma).

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Q: "What are the types of osteosarcoma?"

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Q: "What chemotherapy drugs are used for osteosarcoma?"

MAP Regimen:

• Methotrexate (high-dose with leucovorin rescue)
• Adriamycin (doxorubicin) - cardiotoxicity limit
• Platin (cisplatin) - nephrotoxicity, ototoxicity

Ifosfamide and etoposide may be added for poor responders.

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Related Topics

• Ewing Sarcoma
• Bone Tumour Biopsy Principles
• Limb Salvage Surgery
• Megaprosthesis Complications
• Metastatic Bone Disease