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
String sign in angiography is suggestive of: 
Select and explain. 
A. Aerial dissection, B. Aoa aneurysm, C. Stroke, D. None of the above
A: Aerial dissection
Answer: A: Aerial dissection 
Explanation: 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.