The aorta, which is about 1 inch (2.5 centimeters) in diameter, is the largest artery of the body. It receives oxygen-rich blood from the left ventricle of the heart and distributes it to all of the body except the lungs (which receive blood from the right ventricle). Just after the aorta leaves the heart, smaller arteries that carry blood to the head and arms branch off. The aorta then arches down, with additional smaller arteries branching off along its route from the left ventricle to the lower abdomen at the top of the hipbone (pelvis). At this point, the aorta divides into the 2 iliac arteries, which supply blood to the legs.
The wall of the aorta has 3 layers:
Intima: A thin inner layer
Media: A thick layer between the intima and adventitia
Adventitia: A thin outer layer providing the nutrients for the media
Disorders of the aorta include
Aneurysms: Bulges in weak areas of the walls of the aorta
Dissection: Separation of the layers of the wall of the aorta
These disorders can be immediately fatal, but they usually take years to develop.
Aneurysms also can develop in other arteries of the trunk, arms, and legs (called peripheral arteries), such as the arteries at the back of the knee (popliteal arteries) and the main arteries of the thighs (femoral arteries). The arteries supplying the head (carotid arteries), the arteries supplying the brain (cerebral arteries), and the arteries supplying the heart muscle (coronary arteries) may also develop aneurysms.
A ruptured aneurysm in the brain may cause subarachnoid hemorrhage.
Aortic Aneurysms
The pressure of blood inside the artery forces any weak areas in the artery's wall to balloon outward.
If untreated, an aneurysm may rupture, resulting in pain and internal bleeding serious enough to cause shock and sometimes death.
Location
Aneurysms can develop anywhere along the aorta. Three-fourths of aortic aneurysms develop in the part of the aorta that passes through the abdomen (abdominal aorta), and the rest develop in the part that passes through the chest (thoracic aorta).
In older adults, aneurysms are most likely to occur in areas where arteries branch (for example, where the abdominal aorta branches into the iliac arteries) or in areas of stress (for example, in a popliteal artery).
There are different types of aneurysms. Some may be round (saccular) and others tubelike (fusiform). Most are fusiform.
Where Do Aortic Aneurysms Occur?
Aneurysms can develop anywhere along the aorta. Most develop in the abdominal aorta. The rest develop in the thoracic aorta, most commonly in the ascending aorta. |
Causes
The most common cause of aortic aneurysms is
Atherosclerosis, which weakens the wall of the aorta
Less common causes include
Injuries to the aorta, most often due to a motor vehicle crash
Inflammatory diseases of the aorta (aortitis)
Hereditary connective tissue disorders, such as Marfan syndrome
Some infectious diseases, such as syphilis
In older adults, almost all aneurysms occur in people with atherosclerosis. High blood pressure, which is common among older adults, and cigarette smoking increase the risk of an aneurysm. In people with Marfan syndrome, an aneurysm is most likely to develop in the first part of the aorta, where it emerges from the heart (the ascending aorta).
Complications
The most important complication of aneurysms is rupture. Consequences depend on the size of the rupture. A large rupture may be rapidly fatal, and a small one (sometimes called a leak) may cause warning symptoms that allow people to seek medical care.
A blood clot (thrombus) often develops in the aneurysm because blood flow inside the aneurysm is sluggish. The clot may extend along the entire wall of the aneurysm. A blood clot may break loose (becoming an embolus), travel through the bloodstream, and block arteries. Aneurysms in the popliteal arteries are more likely to produce emboli than aneurysms in other arteries. Occasionally, calcium is gradually deposited in the wall of an aneurysm, making it easier to see on x-ray images.
Aortic Dissection
Aortic dissection occurs when the inner lining of the aorta separates (tears) from the middle layer of the aorta, allowing blood to push between these layers, separating (dissecting) the middle layer of the wall from the still-intact outer layer. As a result, a new, false channel forms in the wall of the aorta. Most people who have an aortic dissection experience pain—typically sudden, excruciating pain, often described as tearing or ripping. As the dissection advances further along the aorta, it can close off the points at which one or more arteries branch off from the aorta, blocking blood flow. The consequences vary depending on which arteries are blocked.
