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: Pathology
Berry aneurysm - defect lies in - 
Select and explain. 
A. Degeneration of internal elastic lamina, B. Degeneration of media/muscle cell layer, C. Deposition of mucoid material in media, D. Low grade inflammation of vessel wall
B: Degeneration of media/muscle cell layer
Answer: B: Degeneration of media/muscle cell layer 
Explanation: Berry's aneurysm is a brain aneurysm caused due to a defect in media. Berry aneurysms arise at the point of weakness in the arterial media, especially branch points in the circle of Willis.
There is a congenital defect in tunica media of cerebral vessels which leads to aneurysm formation.