Berry aneurysms are thought to be due to congenital absence of the media
and internal elastic lamina with ballooning as the blood pulsates through
the vessels over the years.
Ruptures occur when an area becomes thinned and there is a period of hypertension
Berry aneurysms are found incidentally at autopsy 1-2% of the time.
Aneurysms occur in the anterior Circle of Willis 80% of the time. The Anterior
communicating artery and middle cerebral artery at the trifurcation are
the most common sites of origin.