This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skeletal System, Subject name: Radiology
[{'content': "A young child with backache reveals a solitary collapsed dorsal vertebra with preserved intervertebral disk spaces and no evidence of soft tissue mass. The most likely diagnosis is? \nSelect and explain. \nA. Lymphoma, B. Langerhans's cell histiocytosis, C. Ewing's sarcoma, D. Metastases", 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans BThis classic imaging appearance is called Vertebra plana and in children is most commonly seen in Langerhans's cell histiocytosis", 'role': 'assistant'}]