A 15-year-old boy presents with pain and swelling of the proximal tibia. X-ray shows a poorly defined lytic lesion in the metaphysis with a 'sunburst' periosteal reaction and Codman's triangle. Serum alkaline phosphatase (ALP) is markedly elevated. The most likely diagnosis is:

• A Ewing's sarcoma
• B Aneurysmal bone cyst
• C Giant cell tumour
• D Osteosarcoma ✓

Explanation

Classic osteosarcoma (conventional high-grade intramedullary type) presents in the metaphysis of long bones (distal femur > proximal tibia > proximal humerus) in adolescents (peak age 10–20 years). Radiological hallmarks are poorly defined lytic/mixed lesion, periosteal reaction (sunburst pattern, Codman's triangle), and soft-tissue extension. Elevated serum ALP reflects osteoblastic activity and is a useful tumour marker for osteosarcoma but not Ewing's. Ewing's shows a 'onion-skin' periosteal reaction and is diaphyseal. GCT is epiphyseal in skeletally mature patients. ABC is eccentric, expansile, and lacks sunburst.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.