This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdomen: Miscellaneous, Subject name: Anatomy
In subclan steal syndrome there is reversal of blood flow in: 
Select and explain. 
A. Ipsilateral veebral aery, B. Contralateral veebral aery, C. Ipsilateral subclan aery, D. Contralateral subclan aery
A: Ipsilateral veebral aery
Answer: A: Ipsilateral veebral aery 
Explanation: In subclan steal syndrome there is retrograde flow in the veebral aery due to an ipsilateral subclan aery block proximal to veebral aery origin. The block results in lower pressure in the distal subclan aery and upper limb ischemia. Consequently, blood flows from the contralateral veebral aery to the basilar aery and then in a retrograde direction down the ipsilateral veebral aery away from the brainstem.