ABDOMINAL AORTIC ANEURYSM OVERVIEW

An aortic aneurysm occurs when the walls of the main blood vessel that carries blood away from the heart (the aorta) bulge or dilate. An abdominal aortic aneurysm (AAA) is located in the abdominal area, near the navel (figure 1). Aneurysms can also occur in other areas of the aorta, but the abdomen is the most common site. Abdominal aortic aneurysms are not related to aneurysms of the blood vessels in the brain.

Intact abdominal aortic aneurysms cause no health problems. However, large aneurysms can burst, or rupture, and cause heavy bleeding into the abdomen. A ruptured aortic aneurysm is a medical emergency requiring immediate treatment.

ABDOMINAL AORTIC ANEURYSM RISK FACTORS

Abdominal aortic aneurysms (AAA) are uncommon in people under the age of 60. About one person in 1000 develops an abdominal aortic aneurysm between the ages of 60 and 65, and this number continues to rise with age. Screening studies show that abdominal aortic aneurysms occur in 2 to 13 percent of men and 6 percent of women over the age of 65. However, almost 90 percent of the aneurysms identified by screening are small (less than 3.5 cm in diameter) and unlikely to burst.

In addition to age, a number of other factors increase a person's risk of developing an abdominal aortic aneurysm:

• Smoking markedly increases risk for AAA. The risk is directly related to number of years smoking and decreases in the years following smoking cessation.
• Men develop AAAs four to five times more often than women.
• People who are white develop aortic aneurysms more commonly than other groups.
• People with other medical conditions, such as coronary heart disease and peripheral vascular disease, are more likely to develop AAAs.
• A family history of abdominal aneurysm increases the risk of developing the condition and interacts with the risks associated with age and gender. The risk of developing an aneurysm among brothers of a person with a known aneurysm who are older than 60 years of age is as high as 18 percent.

Screening for AAA — A screening test to determine if an AAA is present is recommended in certain groups of people [1]. These recommendations are based upon the increased risk that older men, especially those who smoke or who have a family history of AAA, will develop an AAA.

The test used most commonly to screen for AAA is abdominal ultrasonography. This test is painless and involves the use of a wand, which is applied to the abdomen and uses high frequency sound waves to create an image of the abdominal aorta; aneurysms or other abnormalities can be seen in the image.

A screening test is recommended in the following groups:

• Men who are ages 65 to 75 and who have ever smoked should be screened one time for AAA with abdominal ultrasonography. There is little benefit of repeat screening after a man has a single negative ultrasound. Men older than 75 are unlikely to benefit from screening.
• Men 60 years of age or older who have a sibling or parent with an AAA should have a physical examination and ultrasound screening.
• There is no recommendation to screen women for AAA. Women who are concerned about their risk of AAA, based upon their family history or other risk factors, should discuss their concerns with their healthcare provider.

ABDOMINAL AORTIC ANEURYSM SYMPTOMS

Most abdominal aortic aneurysms are small and do not cause any symptoms. People without symptoms are usually unaware that they have an aneurysm.

Some aneurysms cause a noticeable, small pulsating mass near the navel. This may not be noticed by the patient, but can be detected by a healthcare provider during a routine physical examination. Approximately 30 percent of asymptomatic abdominal aortic aneurysms are discovered in this manner. Other aneurysms are identified during imaging (ie, X-ray, ultrasound, CT scan, MRI) of the abdomen, done for other reasons.

Some aneurysms can cause abdominal or back pain. Such aneurysms are typically detected during an evaluation for pain.

Because blood can pool in the part of the aorta that is bulging, some people develop blood clots inside the aneurysm. If one of these clots breaks loose, it can end up clogging a blood vessel in one of the legs. This can lead to symptoms, such as pain, numbness, or tingling in the leg. In some cases, parts of the leg or foot may even turn pale and become cool to the touch.

Most patients have little warning before rupture. Patients who develop abdominal pain or tenderness may have had a recent increase in aneurysm size, which may predict rupture.

ABDOMINAL AORTIC ANEURYSM TREATMENT

Approximately 15,000 deaths occur each year in the United States due to abdominal aortic aneurysms, usually because of rupture. Once rupture has occurred, the success rate of surgery is much lower than if surgery is performed electively, prior to rupture. The goal of therapy is to treat the aneurysm before rupture.

Aneurysm repair is the primary treatment for aneurysms that are symptomatic or at a high risk for rupture. Repair, however, is associated with other risks and complications. The risk of elective repair must be balanced against the risk of complications or death from an untreated aneurysm. This decision requires understanding of the usual course in patients with untreated aneurysms.

Risk of rupture — The risk of rupture of small aneurysms (smaller than 4.0 centimeters) is much less than the risk of rupture of large aneurysms (larger than 6.0 centimeters). In addition to size, the risk of rupture of an abdominal aortic aneurysm depends on the rate at which the aneurysm is expanding. The evidence suggests that aneurysms expand at an average rate of 0.3 to 0.4 centimeters per year (1 inch = 2.5 cm). The annual risk of rupture based upon aneurysm size is estimated as follows [2]:

• Less than 4.0 cm in diameter = less than 0.5 percent
• Between 4.0 to 4.9 cm in diameter = 0.5 to 5 percent
• Between 5.0 to 5.9 cm in diameter = 3 to 15 percent
• Between 6.0 to 6.9 cm in diameter = 10 to 20 percent
• Between 7.0 to 7.9 cm in diameter = 20 to 40 percent
• Greater than or equal to 8.0 cm in diameter = 30 to 50 percent

There can be significant variability in the rate of expansion, both from one patient to another and for a given patient from year to year. Many patients have long periods with little change in aneurysm size. Larger aneurysms tend to expand faster than smaller aneurysms.

Aneurysms that expand rapidly (for example, more than 0.5 cm over six months) are at high risk of rupture. Growth tends to be more rapid in smokers, and less rapid in patients with peripheral artery disease or diabetes mellitus. Some aneurysms, for unclear reasons, remain relatively fixed in size for a period of time and then undergo rapid expansion. The risk of rupture of large aneurysms (≥5.0 cm) is significantly greater in women than men (18 versus 12 percent) [3].

Other aneurysm complications — Other complications of abdominal aortic aneurysm are less common and not as well recognized. These include:

• Inflammatory aneurysm, swelling and inflammation of the aneurysm wall that causes abdominal pain
• Aorto-venous fistula, an abnormal connection between the aorta and a vein
• Primary aortoenteric fistula, an abnormal connection between the aorta and the bowel
• Thromboembolism, blood clots or debris from the AAA that block blood flow to the legs [4].
• Infected aneurysm

These complications can be limb- and life-threatening, and, when diagnosed, indicate the need for repair.

General treatment principles — In all cases, the decision about whether and when to repair an asymptomatic aneurysm is based upon the risks associated with the aneurysm itself and the risks associated with the repair [5]. Most people with an aneurysm less than 4.0 cm (1.6 inches) in diameter are advised not to have immediate surgery, but rather to follow the aneurysm over time; this is known as watchful waiting. Usually, this involves an ultrasound examination of the abdomen every six months to 3 years, depending on the size of the aneurysm. (See 'Medical treatment' below.)

On the other hand, most patients with an asymptomatic aneurysm greater than 5.5 cm (2.2 inches) in diameter or that expands more than 0.5 cm over a six-month period are advised to have repair. Repair may also be recommended for people with aneurysms that are greater than twice the size of a normal portion of the aorta.

People with an aneurysm between 4.0 and 5.5 cm should discuss their options with a physician. The best approach will depend upon the risk of repair and the risk of aneurysm rupture in an individual patient. Features influencing this decision include:

• The size and rate of growth of the aneurysm.
• The development of symptoms. Patients with aneurysms that become tender to touch or are associated with abdominal or back pain may be advised to have repair even if rupture cannot be demonstrated. Other symptoms that develop that have no other cause and could be related to the aneurysm could be another reason why repair would be recommended.
• The presence of other aneurysms. Patients with aneurysms in other large arteries (such as the iliac, femoral or popliteal arteries of the leg) should have their abdominal aneurysm repaired, usually before, but sometimes at the same time as these other aneurysms.
• Surgical risk. The risk of surgery varies for each individual and the magnitude of risk may be estimated. Patients whose surgical risk is estimated to be high may do better with watchful waiting or less invasive aneurysm repair (see 'Surgical risk' below and 'Medical treatment' below and 'Endovascular stent graft' below).

Medical treatment — Small abdominal aortic aneurysms that are not expanding quickly are usually left alone and watched for changes in size, most often by ultrasound examination of the abdomen every six months. A small aneurysm that grows to be 5.5 cm or larger, or that expands more than 0.5 cm over a six-month period of time should probably be repaired surgically, if possible. (See 'Surgical repair' below.)

Patients being followed with ultrasound, those awaiting repair, or those who have an abdominal aortic aneurysm but whose doctor feels that surgery is too risky, are watched carefully and their medical problems carefully managed. Blood pressure is carefully controlled, and cigarette smoking should be stopped. Also, a medication called a beta blocker may be recommended to slow the rate of aneurysm growth. At least one clinical study showed that people who took beta blockers had a slower rate of growth of their AAA compared with people who took a placebo (0.36 versus 0.68 cm per year) [6].

Patients should call their doctor if they develop abdominal tenderness or back pain. These symptoms may be signs of impending rupture.

Surgical repair — Abdominal aortic aneurysms can be repaired either through “open surgery” or with the use of an “endovascular stent graft” (See 'Open surgery' below and 'Endovascular stent graft' below.) (figure 2). Repair of the aneurysm is recommended if it:

• Causes symptoms,
• Is larger than 5.5 cm (2.2 inches) in diameter,
• Is rapidly expanding, or
• Occurs along with aneurysms in the iliac, femoral or popliteal arteries.

Surgical risk — Surgery of any kind carries certain risks that vary from one person to another, depending upon the patient's general state of health. The surgical risk for repair of an abdominal aortic aneurysm increases with age and the presence of other health conditions. As examples, people who have other heart or lung diseases, and people who smoke are more likely to develop complications such as pneumonia and irregularities in their heart rates after surgery. In addition, older adults are more prone to develop problems (such as cardiac events and stroke) both during and after surgery.

Coronary artery disease is common in people who have abdominal aortic aneurysms. If there are other risk factors for heart disease (such as smoking, diabetes, high blood pressure), the doctor may recommend an evaluation of the heart prior to considering aneurysm surgery. This evaluation may range from a simple exercise stress test to heart catheterization.

Open surgery — Open surgical correction of an abdominal aortic aneurysm involves removing the section of the abdominal aorta that is dilated and replacing it with a prosthesis made of synthetic material (also known as a graft) that is sutured into place (figure 2). This will allow blood to flow normally and the artery wall is used to cover the graft. Planned or elective surgery reduces the risk of rupture of large asymptomatic abdominal aortic aneurysms, and graft failure is uncommon.

Surgery is done in an operating room while the patient is under general anesthesia, and generally takes four to six hours. After surgery, a patient is taken to the intensive care unit for monitoring. Several catheters are used, including a urinary catheter (to drain the bladder), an arterial catheter (to monitor blood pressure), a central venous catheter (to monitor pressures in the heart), an epidural catheter (to give pain medicine), and a nasogastric tube (a tube from the stomach to the nose that is initially used to keep the stomach empty). Patients are generally able to go home after four to seven days, and are able to resume normal activities in about four weeks.

Endovascular stent graft — A less invasive surgical procedure called an endovascular stent graft has shown success in repairing AAAs. It involves making an incision in the groin to expose the femoral artery, placing a wire in the vessel over which a variety of specialized catheters are used to pass a folded graft to the area of the aneurysm (figure 2). Dye is injected to guide the placement of a stent-graft device into the area of the aneurysm. Once the device is correctly positioned, the stent graft is unfolded and expanded with a balloon that pushes it up against the normal aortic wall. This type of graft is not sewn into place. Blood flows through the graft instead of the abnormally dilated aorta, which decreases the pulsations on the aortic wall.

There is less experience and fewer data regarding endovascular stent grafts than surgery, and long-term outcomes are being studied. Stent grafts are primarily performed in older patients who have medical conditions that increase their risk for conventional open surgery.

Comparing two methods of repair — Open surgery is a little riskier in the short term, but it fixes the problem for good. Endovascular repair is less risky in the short term, but it needs to be carefully followed. That’s because endovascular grafts sometimes slip out of place causing an endoleak or kinking the graft. Fixing these problems usually involves a simpler procedure than the first one. If your doctor offers you a choice between the two options, ask:

• What are the risks of each procedure for me?
• What kind of follow-up will I need with each option?
• What is likely to happen if I do not have either treatment?

SUMMARY

Most people with abdominal aortic aneurysms live healthy, symptom-free lives. The decision to undergo surgery involves weighing the risk of aneurysm rupture versus the risks of a surgical procedure. While some general guidelines are suggested based upon the aneurysm size and the rate at which it is enlarging, each treatment decision should be made on an individual basis. Patients should discuss their individual risk of surgery with an experienced healthcare provider to make an informed decision.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient information: Abdominal aortic aneurysm (The Basics)
Patient information: Aortic dissection (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

This topic currently has no corresponding Beyond the Basics content.

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Endovascular repair of abdominal aortic aneurysm
Screening for abdominal aortic aneurysm
Clinical features and diagnosis of abdominal aortic aneurysm
Management of asymptomatic abdominal aortic aneurysm

The following organizations also provide reliable health information.

• Society for Vascular Surgery
  
  (www.vascularweb.org/vascularhealth/Pages/abdominal-aortic-aneurysm.aspx)
• Vascular Disease Foundation
  
  (vdf.org)
• National Library of Medicine
  
  (www.nlm.nih.gov/medlineplus/healthtopics.html)
• National Heart, Lung, and Blood Institute
  
  (www.nhlbi.nih.gov)
• American Heart Association
  
  (www.americanheart.org)

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