Introduction to aortic dissection
The aorta is the large blood vessel that leads from the heart and carries blood to the rest of the body. It originates at the aortic valve at the outlet of the left ventricle of the heart and ascends within the chest to an arch where blood vessels branch off to supply blood flow to the arms and head. The aorta then begins to descend through the chest and into the abdomen where it splits into two iliac arteries that provide blood flow to the legs. Along its descent, more small arteries branch out to supply blood to the stomach, intestine, colon, kidneys, and the spinal cord. As well, at its origin at the aortic valve, coronary arteries branch from the aorta to supply the heart muscle with blood.
The aorta has a thick wall with three layers of muscle that allow the blood vessel to withstand the high pressure that is generated when the heart pumps blood to the body. The three layers are the tunica intima, tunica media, and the tunic adventitia. The intima is the inside layer that is in contact with the blood, the media is in the middle, and the adventitia is the outermost layer.
In an aortic dissection, a small tear occurs in the tunica intima (the inside layer of the aortic wall in contact with blood). Blood can enter this tear and cause the intima layer to strip away from the media layer, in effect dividing the muscle layers of the aortic wall and forming a false channel, or lumen. This channel may be short or may extend the full length of the aorta. Another tear more distal (further along the course of the aorta than the initial tear) in the intima layer can let blood re-enter the true lumen of the aorta.
In some cases, the dissection will cross all three layers of the aortic wall and cause immediate rupture and almost certain death. In most other cases, the blood is contained between the wall layers, usually causing pain felt in the back or flanks.
While there have been different historic classifications of aortic dissection, the Stanford classification is now most commonly used.
- Type A dissections involve the ascending aorta and arch.
- Type B involves the descending aorta.
A patient can have a type A dissection, type B dissection, or a combination of both.
Some patients may experience an aortic dissection without pain and it may be found incidentally on imaging studies performed for other purposes.