1. Draw a diagram of the Circle of Willis and indicate where berry aneurysms 
    commonly occur.
  • 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 or straining., 
  • 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. 
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