An aortic aneurysm is a localized widening or ballooning of the body's largest artery, the aorta. Roughly the diameter of a garden hose, the aorta is the main pathway for oxygenated blood pumped by the heart. Aneurysms can occur anywhere along the aorta, which extends out from the heart up into the chest and down into the abdomen. Approximately 15,000 Americans die annually from complications of their aortic aneurysms.
The danger of an aortic aneurysm is that, like a balloon that is overinflated, the aorta may burst, a potentially deadly situation. Aortic aneurysms can either rupture, hemorrhaging blood into the body cavity, or dissect, leaking blood into the lining of the aorta. Death from a ruptured aortic aneurysm can occur in a matter of seconds.
Although most aneurysms occur in the abdomen, those in the chest cavity are potentially more dangerous; the larger the aneurysm, the greater the risk of rupture or dissection. About one third of the people with a thoracic aortic aneurysm larger than 2.4 inches (5 cm) in diameter will die within five years from a rupture or dissection if the aneurysm is left untreated. However, rupture or dissection can be averted if the aneurysm is diagnosed and repaired, allowing most people with repaired aortic aneurysms to enjoy a normal life span.
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Normally about one inch in diameter, the aorta is the main artery of the body that channels bright red, oxygenated blood from the heart to the rest of the body. The wall of the aorta is elastic, consisting of three layers that stretch to accommodate the surge of blood flowing into the artery as the heart contracts. The aortic wall is lined with a thin layer of smooth cells, beyond which is a thick middle muscular layer that is surrounded by a tough outer layer of tissue.
As it passes through the chest and the abdomen, the aorta is shaped like an old-fashioned candy cane. The ascending aorta is the short section of the candy cane, emerging from the left ventricle of the heart. It extends up into the chest into the aortic arch, the U-turn of the candy cane. The aortic arch is where the aorta transitions from the front to the back of the chest and where the arteries that supply the head and upper body with blood branch off the aorta. The aorta then straightens out and descends into the abdomen.
The vessels that supply blood to the spinal column and midsection of the body branch off from the aorta along the straight section known as the descending aorta. The upper segment of the descending aorta, called the descending thoracic aorta, the aortic arch, and the ascending aorta together make up the thoracic aorta. The abdominal aorta, the section of the descending aorta below the diaphragm, eventually splits into the two iliac arteries that carry blood to the pelvis and legs.
Aneurysms can form anywhere along the aorta as either a symmetrical bulge around the aorta or an asymmetrical bleb. Fusiform aneurysms occur as a symmetrical bulge around the entire circumference of a section of the aorta. Saccular aneurysms form as a small blister or bleb on one side of the aorta. Many saccular aneurysms are either caused by trauma such as a motor vehicle accident or are the result of a penetrating aortic ulcer. Aneurysms are further classified based on their location along the aorta.
- Thoracic aortic aneurysms are those that occur along the aorta above the diaphragm, the partition between the chest and abdomen, including the ascending aorta, the aortic arch, and the descending thoracic aorta. Up to 25 percent of aortic aneurysms are thoracic; of these, ascending aortic aneurysms are the most common, followed by descending thoracic aneurysms. Aneurysms along the aortic arch are rare and are the most complex to treat, largely because the arterial branches that supply blood to the brain and upper extremities are attached along the aortic arch. Thoracic aortic aneurysms are potentially the most lethal; as many as 1 out of every 5 people die within five years if a thoracic aneurysm is left untreated. Larger aneurysms are more dangerous, because of the increased risk of rupture or dissection.
- Abdominal aortic aneurysms are located along the segment of the aorta that extends beyond the diaphragm through the abdomen. About 75 percent of aortic aneurysms are located in the abdomen. They can affect anyone, but most are associated with smoking and high blood pressure and occur primarily in men over age 60.
- Thoraco-abdominal aortic aneurysms span both the thoracic and abdominal segments of the aorta. These aneurysms are relatively uncommon, and treatment can require replacement of the entire aorta. This involves reconnecting critical blood vessels that branch off the aorta along the lower descending thoracic aorta and upper abdominal aorta that supply blood to the spinal cord. Repair of thoraco-abdominal aortic aneurysms carries a significant risk of paraplegia and requires specific surgical expertise.
Aortic dissections can cause aortic aneurysms or result from them. An aortic dissection begins with a tear through the inner layer into the middle layer of the aortic wall. This causes the layers of the aortic to separate like plywood that has been left outside in the weather.
This separation within the wall (dissection) of the aorta causes the wall of the aorta to weaken, often enlarging the aorta, forming an aneurysm. Frequently, a second tear forms farther along the aorta; that opens a path for the blood to get back into the vessel, forming a side channel for blood flow in the lining of the aorta and creating a "double-barreled" aorta.
Dissections can occur anywhere along the aorta or involve the entire aorta. Blood leaking into a dissection near the heart may cause a cardiac tamponade-a life-threatening condition where blood enters the lining around the heart, preventing the heart from filling properly. If the tear progresses completely through the aorta, death can occur in a matter of minutes.
When the aorta dissects, severe pain in the chest or back occurs, which is often described as a tearing discomfort––"the worst pain I've ever had," many patients say. This usually sends the person to the emergency room where the diagnosis can be made. If left untreated, most aortic dissections are fatal.
The risk of death depends upon the extent of the dissection. The risk is highest for dissections that involve the ascending aorta. For that reason, most aortic dissections along the ascending aorta are treated immediately with surgery. Occasionally, some specific variations of dissections along the descending thoracic aorta may be treated with medication.
Most frequently, aortic aneurysms are caused by the breakdown of the muscular layer and the elastic fibers within the wall of the aorta. The breakdown usually occurs over time, as aging takes its toll along with, in some people, prolonged high blood pressure or smoking. As the tissues of the aorta begin to break down, the aortic wall weakens, and the blood pressure within the aorta causes the wall to stretch beyond its capacity, forming an aneurysm.
Aortic aneurysms can also form suddenly, when the wall of the aorta is torn. These aneurysms are known as pseudoaneurysms because the aortic wall is not intact. Pseudoaneurysms are usually caused by trauma such as a motor vehicle accident. Less frequently, pseudoaneurysms can form because of the buildup of atherosclerotic plaque in the aorta. Atherosclerotic plaque can cause the formation of penetrating aortic ulcers, an inflammation that can penetrate the wall of the aorta, weakening it and allowing a pseudoaneurysm to form. Penetrating aortic ulcers can also lead to aortic dissections.
In general, aortic aneurysms occur more frequently in men and in people over age 60. Often there is a family history of aortic aneurysms or an association with bicuspid aortic valve (a congenital defect in the valve connecting the aorta to the heart), smoking, or high blood pressure. Some well-characterized genetic conditions such as Marfan syndrome are associated with a high risk of aneurysm. But sometimes there is no apparent reason for this ballooning of the aorta.
The primary risk factors for aortic aneurysms include the following.
- Prolonged hypertension. High blood pressure is the fuel of an aneurysm; having blood pressure that is not well controlled increases one's risk of developing an aortic aneurysm.
- Smoking. Smoking leads to degeneration of the elastic tissue all over the body, including that within the wall of the aorta, predisposing one to aortic aneurysm.
- Age. With time the wall of the aorta wears out; most people with aortic aneurysm are over age 40.
- Being male. Abdominal aortic aneurysms are more prevalent in men.
- Family history. Thoracic aortic aneurysms tend to run in families, so it's important to inform immediate family members of your condition so that they can discuss the need to be evaluated for aortic aneurysm with their doctors.
There are also other medical conditions that can lead to or are associated with a weakened aorta, predisposing one to developing an aortic aneurysm. These include:
- Marfan syndrome, a disorder of the connective tissue, increases the risk for aortic aneurysms.
- Bicuspid aortic valve, a congenital heart defect, predisposes one to aortic aneurysm; up to 50 percent of the people with a bicuspid aortic valve also have an ascending aortic aneurysm.
- Inflammatory diseases including giant cell arteritis, an inflammatory disease of the blood vessels, can predispose one to aortic aneurysms.
- Atherosclerosis can lead to inflammations of the aortic wall known as penetrating aortic ulcers, which can cause an aortic aneurysm and/or dissection.
Last reviewed on 2/10/2009
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