Most aortic aneurysms are caused by atherosclerosis. As atherosclerosis worsens, the aortic wall becomes weak or damaged. Over time, the constant pressure of blood coursing through a weakened aorta can cause a section of it to slowly enlarge, forming a bulge — an aneurysm.

• atherosclerosis

• High blood pressure

• Nicotine dependence

Atherosclerosis is a slow process, often taking decades to develop. A diet high in cholesterol and fat is a major risk factor for atherosclerosis. Smoking and high blood pressure also can contribute to atherosclerosis and aneurysm formation.

Some people are born with a weakness in an artery wall, such as those with a rare, inherited condition called Marfan syndrome. Rarely, bacteria can infect the aorta and weaken a section of its wall. Thoracic aneurysms can result after traumatic injury to the chest — such as when the chest impacts the steering wheel in a motor vehicle crash. Sometimes, however, the cause of an aortic aneurysm isn't clear.

An aortic aneurysm is different from a condition known as aortic dissection. Artery walls consist of three layers — a thin inner layer, a muscular middle layer and a tough outer layer. In aortic dissection, a tear occurs in the aortic wall. This allows bleeding into and along the aortic wall.

Risk factors

Age plays a role in the development of aortic aneurysms. People older than 55, particularly men, are at increased risk. In addition, smoking or having high blood pressure raises your risk of developing an aortic aneurysm.

• High blood pressure

• Nicotine dependence

Some inherited conditions, such as Marfan syndrome, weaken the aorta. Marfan syndrome is a disease of the connective tissue in the body. Children with Marfan syndrome often have physical deformities, including a deformed breastbone and enlargement of the aorta near the heart.

Abdominal aneurysms may run in families. If you have a sibling who has had an aortic aneurysm, talk to your doctor about your risk. If you're at high risk, your doctor may recommend periodic screening.

Screening and diagnosis

In some cases, an aortic aneurysm is discovered during a physical examination. Your doctor may feel a pulsating bulge in your abdomen. Or by placing a stethoscope on your chest or abdomen, your doctor may be able to pick up sounds of turbulent blood flow through an aortic aneurysm. But most aortic aneurysms are found incidentally during routine medical tests, such as a chest X-ray or ultrasound.

If you need further evaluation, your doctor may use other, more specialized tests. These tests might include a computerized tomography (CT) scan or magnetic resonance imaging (MRI) scan. In a CT scan, you lie still on a movable table that's guided into a machine that looks like an enormous doughnut. There, X-ray scanners create detailed images of the organs and blood vessels in your chest and abdomen. It's painless and generally takes less than 10 minutes. In an MRI scan, a cylinder-shaped machine scans your body using magnetic fields, creating a computer image of soft tissues of your body, including the shape of your aorta.

If an aneurysm becomes calcified — which is a marker for the presence of atherosclerosis — it will show up on an X-ray. Otherwise it will be visible only using ultrasound or a CT or MRI scan.

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Complications

Aneurysms are serious because they may rupture, causing life-threatening internal bleeding. In general, the larger the aneurysm, the greater the risk of rupture. The risk of rupture is high when an aortic aneurysm exceeds 2 inches (about 5 centimeters, or cm) in diameter. Normally, the diameter of a healthy aorta ranges between 3/4 inch and 1 inch (about 2 to 2.5 cm).

Symptoms that an aortic aneurysm has ruptured — which is a medical emergency — include sudden, intense and persistent abdominal pain that may radiate to the back or legs, with sweatiness, clamminess, dizziness, low blood pressure, fast pulse and possible loss of consciousness. 

Aortic aneurysms can house small blood clots. These clots may break loose and block a blood vessel downstream from the aneurysm, causing pain or potentially life-threatening problems, such as a ministroke (transient ischemic attack, or TIA) or a full-blown stroke.

• Abdominal pain

• Stroke