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: Surgery
[{'content': 'String sign in angiography is suggestive of: \nSelect and explain. \nA. Aerial dissection, B. Aoa aneurysm, C. Stroke, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Traditional angiography remains the basis of diagnosis and characterization of aerial dissection. Angiographic abnormalities include stenosis of the true lumen, or "string-sign," visible intimal flaps, and the appearance of contrast in the false lumen. Four-vessel cerebral angiography should be performed when suspicion of dissection exists. Ref: Schwaz\'s principle of surgery 9th edition, chapter 42.', 'role': 'assistant'}]