The defect in berry aneurysm is
Degeneration of internal elastic lamina
Degeneration of media
Deposition of mucoid material in media
Low grade inflammation of vessel wall
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
Nervous system