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: Medicine
Which is least common site of berry aneurysm: 
Select and explain. 
A. Basilar aery, B. Veebral aery, C. Anterior cerebral aery, D. Posterior cerebral aery
B: Veebral aery
Answer: B: Veebral aery 
Explanation: Answer is B (Veebral aery): About 85% (Harrison) to 90% (Robbins) aneurysms occur in the Anterior circulation, on the circle of Willis. Posterior circulation as inveebral aery is a very uncommon location for berry aneurysm. In order of frequency of occurrence the location of - Anterior communicating - Ant. cerebral junction (29%). - Post communicating - Internal carotid junction (28%). - Middle cerebral bifurcation (18%). - Intracranial carotid bifurcation (8%) - Veebrobasilar or basilar bifurcation (3%)