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
Onion skin periosteal reaction is usually seen in: 
Select and explain. 
A. Ewings sarcoma, B. Osteosarcoma, C. Wilms tumor, D. Osteoblastoma
A: Ewings sarcoma
Answer: A: Ewings sarcoma 
Explanation: 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