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: Anatomy
The defect in berry aneurysm is 
Select and explain. 
A. Degeneration of internal elastic lamina, B. Degeneration of media, C. Deposition of mucoid material in media, D. Low grade inflammation of vessel wall
B: Degeneration of media
Answer: B: Degeneration of media 
Explanation: Multiple aneurysms are observed in about 20-30% of cases of berry aneurysm. Such aneurysms are congenital in that defect in aerial wall may be present from bih, but actual aneurysm develops over years; thus, rupture is most likely to occur in middle-aged adults. Refer Robbins page no 1270