This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ohopaedics Q Bank, Subject name: Orthopaedics
[{'content': 'Onion skin periosteal reaction is usually seen in: \nSelect and explain. \nA. Ewings sarcoma, B. Osteosarcoma, C. Wilms tumor, D. Osteoblastoma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ewing sarcoma Destructive lesion in the diaphysis of a long bone with an "onion skin" periosteal reaction. Originates in the metaphysis of a long bone, but frequently extends for a considerable distance into the diaphysis. Classically, PNET class of tumour, with c-myc positive,having round cells is histology. -Osteosarcoma show codman\'s triangle, sunray or sunburst appearance as periosteal reaction', 'role': 'assistant'}]