The anatomy of aortic aneurysms

When the First Gentleman Jose Miguel Arroyo first underwent a successful surgery for the repair of an aortic aneurysm in April 2007, many people had never heard, much less know much, about this condition. Many may have known of someone who developed a stroke from the rupture of a cerebral aneurysm (the blood vessel in the brain) but not of the aorta, the main artery which supplies oxygen-rich blood to all parts of the body.

Your aorta is a cane-shaped blood vessel that exits from the top of the heart and curves downward passing through the chest (thorax) and stomach (abdomen). Please refer to diagram. Major arteries branch off from the aorta to supply blood to the brain, arms, internal organs, and legs.

An aneurysm is an abnormal dilation of a blood vessel. It occurs when the wall of an artery, such as the aorta, becomes weak or damaged. Over time, the constant pressure of blood flowing through the weakened area can cause a section of the aorta to slowly enlarge. Thus, an aneurysm dilates the aorta like a balloon. The bigger it gets, the thinner the wall gets and the risk of rupture increases.

Aneurysms can occur anywhere on the aorta but about 75 percent occur in the abdomen and are called abdominal aortic aneurysm (AAA). Most of the remainder occur nearer to the heart and are called thoracic aortic aneurysm (TAA). If an aneurysm ruptures, internal bleeding occurs, and it is often fatal — for example, 75 percent of patients with a ruptured AAA die.

Factors Of Formation

The walls of a healthy aorta are very elastic and can stretch and relax as needed to accommodate pulses of blood from the heart. But with age, the aorta becomes less elastic. That’s one reason why most AAAs occur in adults over 60 — but it’s seldom the only reason. The weakening and breakdown of the aortic wall where the aneurysm forms is usually accelerated by other factors, including:

• Smoking. It’s estimated that about 90 percent of people who develop aneurysms have smoked at some point in their lives.

• High blood pressure (hypertension). Over a period of years, excess pressure that hypertension puts on your arteries can cause them to weaken and lose elasticity.

• Artery clogging and hardening (atherosclerosis). This is the buildup of cholesterol-containing fatty deposits on artery walls that can damage the artery lining.

A number of less common factors may also contribute to aortic aneurysms. In addition, men are more likely to have an aortic aneurysm than are women, and aortic aneurysms can run in families.

Discovering A Problem

An enlarging AAA may produce some symptoms, such as a pulsing sensation near the navel, tenderness or pain in the abdomen, or back pain. However, it’s more common for aortic aneurysms to occur without symptoms. They are frequently discovered during a routine physical examination, through a CT scan or ultrasound of the abdomen, or on an x-ray of the chest area that’s being done for another purpose.

Generally, aortic aneurysms are too rare to warrant widespread screening. However, certain groups, for which an ultrasound screening test may be appropriate, include:

• Men who are 65 and older who smoke or who have smoked.

• Men who are 50 and below — and women who are 60 and older — who have a parent or sibling who has had an aortic aneurysm.

Preventing Rapid Growth

Once a bulging aneurysm begins to form in your aorta, your aorta will never heal and return to normal. Many aneurysms will eventually need to be repaired surgically — but it’s not always necessary to do it right away.

If your AAA is small, appears to be growing slowly and isn’t causing any symptoms, your doctor may recommend a “wait-and-watch” approach, using imaging tests one to two times a year to assess the size and growth rate of your aneurysm.

You may be able to minimize aneurysm growth and the risk of rupture — and to maximize the overall health of your arteries by:

• Stopping smoking and avoiding secondhand smoke.

• Treating hypertension, which typically involves taking one or more drugs to lower blood pressure, but may also be helped by limiting your sodium intake.

• Getting regular, moderate exercise, such as walking.

• Avoiding activities that cause prolonged elevation of blood pressure, such as long periods of strenuous activity.

• Improving cholesterol levels, which may be achieved with medication and by eating a diet low in saturated fat and cholesterol and high in fruits, vegetables, and other high-fiber foods.

The medications most commonly used to treat aneurysms are beta blockers, such as metoprolol and propanolol, and calcium channel blockers, such as amlodipine and nifedipine.

Dissection Of The Aorta

The walls of your aorta are made of three tissue layers. In some cases, a tear can occur within the aortic wall, causing these layers to dissect (separate). This can hamper blood flow throughout your body and can cause the aorta to weaken and enlarge, putting it at risk of rupture (see diagram).

A rupture or dissection of your aorta is a sudden event that often feels like a ripping sensation down your back to your groin or between your shoulder blades. The pain can be intense, but it can also be somewhat dull. You may also feel clammy, lightheaded or dizzy. If you know you’re at risk of aortic aneurysm rupture, be aware of these symptoms and seek emergency care if they occur.

Surgical repair of a dissecting aorta may be required if blood supply to your organs isn’t adequate — or if the area of dissection is rapidly expanding or located on the part of the aorta nearest the heart.

But in many cases, simply lowering your blood pressure is enough to allow the dissection to heal enough so that immediate surgery can be avoided. Careful, lifelong monitoring of the area will be necessary to watch for aneurysm development and growth.

Surgical Options

With larger aneurysms, surgery is often considered. Surgery may also be considered if a smaller aneurysm is enlarging rapidly or is leaking. Deciding whether to go ahead with surgery involves numerous factors, one of which is to assess your overall health to determine whether the risk of your aneurysm rupturing is greater than your risk of having surgery to repair it.

Not all AAAs require repair. The guidelines are that aneurysms greater than 5.5 centimeters in men and greater than 5 centimeters in women require repair.

The two main types of surgery are:

• Open-abdominal or open-chest surgery. This is the standard operation to repair an aortic aneurysm. It involves making an incision in the front or side of your abdomen or chest so that the damaged section of your aorta can be removed and replaced with a graft — a small tube made of synthetic material such as Dacron or Teflon — that is attached to the aorta on both ends. This surgery is generally successful and requires the least amount of follow-up care. It’s also more durable over the long term. The odds of needing a repeat procedure to repair a problem is less than two percent.

• Endovascular surgery. This newer procedure may be an option in many situations as a way to avoid major surgery — and may be a better choice only for those who are over 70 or who are at higher risk of complications from open surgery. With the endovascular approach, a synthetic graft is inserted into an artery in the leg and maneuvered to the aorta. Using x-ray guidance, the graft is positioned and expanded into place.

Endovascular surgery generally carries fewer risks than does open surgical repair and you can expect a recovery period of days, rather than weeks. However, follow-up appointments are needed on a more frequent basis and the likelihood of needing a repeat procedure is 10 percent to 20 percent. In addition, it’s not known how well these repairs hold up over the long term.

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Source: Endovascular AAA Repair Less Risky Than Open Surgery for Older Adults. Cleveland Clinic Heart Advisor, January 2010 or www.Heart-Advisor.com; and Journal of Vascular Surgery, October 2009