7 years old child presents with a lesion in upper tibia. X-ray shows a radiolucent area with Codman's triangle and Sunray appearance. Diagnosis is -

Codman's triangle and sunray appearance are typical of osteosarcoma. However, you should keep in your mind following very important facts : - Sunray (sunburst) appearance and Codman's triangle indicates periosteal reaction (periosteal new bone Both these are typical of osteosarcoma but may also occur in other rapidly growing bone tumours sarcoma), and infection (osteomyelitis). Similarly, onion peel appearance indicates periosteal new bone-formation and is typical for Ewing's sarcoi. this can also occur in osteosarcoma and osteomyelitis. The crux is that aggressively growing tumours and infection stimulate the periosteum which then reacts by fon. new bone, (therefore it is called periosteal reaction) which may take any of the above forms.