This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory, Subject name: Medicine
[{'content': 'A 40-year-old man has a routine CXR, which reveals a posterior mediastinal mass. Which of the following is the most likely diagnosis? \nSelect and explain. \nA. lipoma, B. neurogenic tumor, C. esophageal cyst, D. fibroma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Neurogenic tumors are the most common posterior mediastinal masses. Other posterior mediastinal masses include meningoceles, meningomyeloceles, gastroenteric cysts, and esophageal diverticula. Common anterior mediastinal masses include thymomas, lymphomas, teratomas, and thyroid masses. Middle mediastinal masses include vascular lesions, lymph nodes, and pleuropericardial and bronchogenic cysts.', 'role': 'assistant'}]