This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Radiology
[{'content': 'What is not a feature of carotico-cavernous fistula? \nSelect and explain. \nA. Pulsatile exophthalmos, B. Generally post traumatic, C. Dilated superior ophthalmic vein, D. Can lead to spontaneous intra orbital hemorrhage', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans DCaraticocavernous fistula is mostly secondary to penetrating trauma associated with fractures of the facial bone and this leads to pulsatile exophthalmos which coincides with pulse. On imaging the shunting of blood from artery to vein is so fast that only the superior ophthalmic vein which is carrying extra blood volume is identified. The actual fistula can be demonstrated on digital subtraction angiography', 'role': 'assistant'}]