This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Imaging of Musculoskeletal Tumors, Subject name: Radiology
[{'content': "Onion - peel appea ranee is seen in - \nSelect and explain. \nA. Ewing's sarcoma, B. Osteoma, C. Osteosarcoma, D. Osteoclastoma", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. is \'a\' i.e., Ewing\'s sarcoma o Onion - peel periosteal reaction is characteristically seen in Ewing\'s sarcoma.Note - Onion - peel periosteal reaction may also be seen rarely in osteosarcoma,o Codman\'s triangle is characteristically seen in osteosarcoma. It may also be seen in Ewing\'s sarcoma and osteomyelitis. Characteristic radiological features of few bone tumorso Celery-stick appearanceEnchondromaso Coat-hanger appearanceOsteochondromao Codman tumor and chicken-wire calcificationChondroblastomao Double density sign on radionuclide scanOsteoid osteomao Nidus and sclerotic rimOstoid osteomao "Driven snow" appearancePindborg tumoro Fallen fragment/Hinged fragment signSimple (unicameral) bone cysto "Eggshell" covering of expansile cortex over surface of lesionABCo \'Soap bubble\' appearance.ABCo Soap bubble appearance (& goes into corners)GCT (Osteoclastoma)o \'Floating tooth\' signEosinophilic granuloma, adamantinomao Onion skin (onion peel) appearanceEwing sarcomao Skip lesionsOsteosarcoma, Ewings sarcomao \'Sunray/Sunburst\' appearanceOsteosarcomao String sign (to differentiate from myositis ossificans)Parosteal osteosarcomao Popcom/mottled calcificationChondrosarcomao Shepherd\'s crook deformityFibrous dysplasia* Codman\'s triangleOsteosarcoma, Ewing sarcomao Winking owl signMetastasis to pedicles of vertebrao Corduroy/accordian vertebra/vertical striationsVertebral hemangiomao Polka dot sign on CTVertebral hemangiomao Geographical skullEosinophilic granulomao Hole-within-a-hole lesionEosinophilic granuloma', 'role': 'assistant'}]