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: Ophthalmology
The most common cause of pulsating exophthalmos is: 
Select and explain. 
A. Orbital varices, B. Neurofibromatosis, C. Cavernous haemangioma, D. Caroticocavernous fistula
D: Caroticocavernous fistula
Answer: D: Caroticocavernous fistula 
Explanation: Ans. Caroticocavernous fistula