Paper II
Question
Radiologic and morphological features of osteogenic sarcoma
Answer
Osteogenic sarcoma (osteosarcoma) is the most common primary malignant bone tumour, typically affecting the metaphysis of long bones (distal femur, proximal tibia, proximal humerus) in adolescents/young adults.
Radiological features:
- Destructive, mixed lytic and sclerotic (blastic) lesion in the metaphysis.
- Codman triangle — periosteal new bone formation at the margin of the lesion where the tumour lifts the periosteum.
- “Sunburst” or “sunray” appearance — spicules of reactive bone radiating perpendicular to the shaft cortex, reflecting the tumour breaking through cortex and periosteum.
- Cortical destruction with soft tissue extension.
Morphological (microscopic) features:
- Anaplastic, pleomorphic malignant spindle/polygonal cells with marked nuclear atypia and frequent, often abnormal, mitoses.
- Hallmark: direct production of osteoid or immature woven bone by the malignant tumour cells (this is the defining diagnostic feature distinguishing it from other sarcomas).
- Variable amounts of cartilaginous or fibrous differentiation may be present (chondroblastic, fibroblastic subtypes).
- Areas of necrosis and haemorrhage are common; vascular invasion often seen.
- Gross: Grey-white, gritty (due to bone formation), haemorrhagic mass destroying cortex and extending into soft tissue, with a wide zone of transition.