What is aortic dissection?
Aortic dissection is a rare, but potentially fatal, condition in which blood passes through the inner lining and between the layers of the aorta. The dissecting aorta usually does not burst, but has an abnormal second channel within it. Aortic dissection is due to a partial tear in the main artery from the heart (aorta), which causes a separation (dissection) of the layers of the aortic wall and bleeding into and along the wall of the aorta. Aortic dissection is a life-threatening condition.
Doctors also refer to it as a dissecting aneurysm.
A defect in the inner lining of the aorta allows an opening or tear to develop. The aorta is the main artery of the body and is an area of high blood pressure. When a defect develops, blood pressure can force the tear to open and allow blood to pass through. Since the blood is under pressure, it eventually splits (dissecting) the middle layer of the blood vessel, creating a new channel for blood. The length of the channel grows over time and can result in the closing off of connection points to other arteries. This can lead to heart attack, strokes, abdominal pain, and nerve damage. Blood may leak from the dissection and collect in the chest an around the heart. A second mechanism leading to aortic dissection is medial hemorrhage. A medial hemorrhage occurs in the middle layer of the blood vessel and spills through the inner lining of the aorta wall. This opening then allows blood from the aorta to enter the vessel wall and begin a dissection.
As with all other arteries, the aorta is made up of three layers. The layer that is in direct contect with the flow of blood is the tunica intima, commonly called the intima. This layer is made up of mainly endothelial cells. Just deep to this layer is the tunica media, known as the media. This "middle layer" is made up of smooth muscle cells and elastic tissue. The outermost layer (furthest from the flow of blood) is known as the tunica adventitia or the adventitia. This layer is composed of connective tissue. In an aortic dissection, blood penetrates the intima and enters the media layer. The high pressure rips the tissue of the media apart, allowing more blood to enter. This can propagate along the length of the aorta for a variable distance, dissecting either towards or away from the heart or both. The initial tear is usually within 10cm of the aortic valve. The risk in aortic dissection is that the aorta may rupture, leading to massive blood loss resulting in death.
Several different classification systems have been used to describe aortic dissections. The systems commonly in use are either based on the anatomy of the dissection or the duration of onset of symptoms prior to presentation. There are two types of aortic dissections, although sometimes both are required:
Type A: A dissection to the ascending aorta is classified as a Type A dissection. These dissections can be treated medically (usually only briefly) or with interventional catheterization or open surgical techniques.
Type B: A dissection of the descending aorta is classified as a Type B dissection. These dissections are most often treated medically with routine monitoring and prescribed medications. There is a surgical option, but it carries substantially increased risk of paralysis.
DeBakey classification system
The DeBakey system is an anatomical description of the aortic dissection. It categorizes the dissection based on where the original intimal tear is located and the extent of the dissection (localized to either the ascending aorta or descending aorta, or involves both the ascending and descending aorta.
Type I - Originates in ascending aorta, propagates at least to the aortic arch and often beyond it distally.
Type II – Originates in and is confined to the ascending aorta.
Type III – Originates in descending aorta, rarely extends proximally.