Aortic dissection occurs when the layers of the aorta separate. The aorta is the main artery leading from the heart. Arterial walls have three layers. A tear in an inner layer can admit blood under pressure that works its way between layers, causing the layers to dissect apart or separate. This process can squeeze off the main channel so that blood cannot get through the main aorta or any of its branches.

This is a life-threatening event since it can cause stroke, sudden heart failure, or death to impaired blood flow to a number of vital organs. The enlarging mass of misdirected blood can also compromise nearby structures such as the airways, lungs, or heart. Or it may rupture with catastrophic bleeding.

Heart and Main Vessels
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Elevated blood pressure and a diseased aorta are the principal causes, usually due to atherosclerosis. Other congenital and acquired afflictions of the aorta also increase the chances of dissection.