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:
| Test | Result | Normal Range | Interpretation |
|---|---|---|---|
| Hb | 142 g/L | 130-170 g/L | Normal |
| WCC | 6.8 ×10⁹/L | 4-11 ×10⁹/L | Normal |
| Platelets | 285 ×10⁹/L | 150-400 ×10⁹/L | Normal |
| CRP | 12 mg/L | <5 mg/L | ↑ Mildly elevated |
| ESR | 40 mm/hr | <15 mm/hr | ↑ Elevated |
| ALP | 280 U/L | 50-150 U/L | ↑↑ Significantly elevated |
| LDH | 450 U/L | 140-280 U/L | ↑ Elevated |
| Calcium | 2.4 mmol/L | 2.2-2.6 mmol/L | Normal |
Image 1: AP and Lateral Radiograph of Left Distal Femur
Radiological features:
Image 2: MRI Left Femur (Whole bone with joints above and below)
MRI findings:
Image 3: CT Chest
Findings:
Describe the radiographic features using the ABCDS approach
What is your differential diagnosis?
What further investigations would you request and why?
How would you perform a biopsy of this lesion?
The biopsy confirms high-grade conventional osteosarcoma. Describe the management pathway.
What is the prognosis and what factors affect it?
This pattern suggests Osteosarcoma:
Distinguish from Ewing Sarcoma:
| Feature | Osteosarcoma | Ewing Sarcoma |
|---|---|---|
| Peak age | 10-25 years | 5-15 years |
| Location | Metaphysis | Diaphysis |
| Bone | Long bones around knee | Any bone, flat bones common |
| Periosteal reaction | Sunburst | Onion-skin (lamellated) |
| Matrix | Osteoid (cloud-like) | None (purely lytic) |
| Histology | Osteoid production | Small round blue cells |
| Chromosomes | Complex | t(11;22) EWS-FLI1 |
Distinguish from Osteomyelitis:
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:
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).
Q: "What are the types of osteosarcoma?"
| Type | Features | Prognosis |
|---|---|---|
| Conventional (high-grade) | 80-90%, metaphyseal, aggressive | Standard (60-70% survival) |
| Telangiectatic | Lytic, blood-filled, can mimic ABC | Similar to conventional |
| Small cell | Mimics Ewing | Similar to conventional |
| Parosteal (low-grade surface) | Posterior distal femur, dense, wraps around | Excellent (>90% survival) |
| Periosteal (intermediate) | Surface, chondroblastic | Good (80-85% survival) |
| High-grade surface | Surface, aggressive | Similar to conventional |
| Secondary | Arises in Paget's, irradiated bone | Very poor |
Q: "What chemotherapy drugs are used for osteosarcoma?"
MAP Regimen:
Ifosfamide and etoposide may be added for poor responders.