This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'To diagnose thymoma in a case of mediastinal mass is: \nSelect and explain. \nA. Thoracotomy and biopsy, B. FNAC, C. Chest CT scan, D. Somatostatin receptor imaging', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Once a mediastinal mass is detected, Next step: 1. Initial mediastinoscopy or limited thoracotomy to get sufficient tissue to make an accurate diagnosis. 2. Fine-needle aspiration is poor at distinguishing between lymphomas and thymomas 3. Subsequent staging of thymoma can be done with chest CT scans 4. MRI has a defined role in the staging of posterior mediastinal tumors 5. Somatostatin receptor imaging with indium-labeled somatostatin analogues also used for staging Ref: Harrison, E-18, chapter e-20.', 'role': 'assistant'}]