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Abdominal aortic aneurysm (AAA)

An aneurysm is a condition that involves weakening in the walls of a blood vessel, causing it to enlarge or dilate. Aneurysms can form in any blood vessel in the body, but are most commonly seen in the main artery known as the aorta, at the level below the kidney arteries (Figure 1A). This is known as an abdominal aortic aneurysm (AAA). The greatest risk associated with an aneurysm is rupture, causing internal bleeding. This happens because the aortic wall continues to dilate and weaken against the flow of blood through the vessel. The rupture of an aneurysm is a life-threatening situation with a high chance of death.

Figure 1. Abdominal aortic aneurysm. (A) An unrepaired infrarenal AAA. (B) Endovascular repair of an AAA using an abdominal stent graft. (C) Open repair of an AAA with an illustration depicting the removal of diseased aorta and synthetic graft material being sewn into place. (Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2014. All Rights Reserved.)

Who is at risk of developing an AAA?

Abdominal aortic aneurysms are most common in older adults. They occur in up to 6% of men and 1% of women over the age of 65 years.1

Smoking is a major risk factor for AAAs, and the risk is directly related to the number of cigarettes smoked.2 Individuals are at a higher risk of developing AAAs if they have a family history of AAAs or other aneurysms. People who have a first-degree relative (parent, sibling, or child) with an AAA have a much higher risk (approximately 15–29%3) of developing an aneurysm, and are likely to have aneurysms in more than one area.4 High blood pressure is also well known to be associated with aneurysm disease and should be controlled. Connective tissue disorders such as Marfan syndrome, Loeys-Dietz syndrome or Familial Thoracic Aneurysm disease are also often associated with the development of aortic aneurysm, which may also include other parts of the aorta.5Table 1 provides a summary of AAA risk factors.Table 1. Risk factors for abdominal aortic aneurysm (AAA).

Populations at risk
Older adults (men and women >65 years)
Risk factors
• Smoking
• High blood pressure
• Family history of AAA or other aneurysms
• Connective tissue disorders (Marfan syndrome, Loeys-Dietz syndrome, and others)

What are the signs and symptoms?

Abdominal aortic aneurysms develop slowly and may go undetected for many years. AAA often presents with no symptoms until rupture. Aneurysm rupture occurs when the wall of the aorta becomes severely weakened by the expansion of the aneurysm sac and tears open. When the sac ruptures, bleeding occurs inside the body. Aortic dissection, or a tear between the layers in the wall of the aorta, can also occur.

Symptoms of aortic aneurysm rupture include pain in the abdomen (throbbing, aching or sharp pain, often sudden), pain in the back, nausea, vomiting, fainting, and systemic shock. AAA rupture is a life-threatening event with a high risk of severe complications and death. The risk of death from AAA rupture is approximately 60–80%,1 meaning that many patients collapse before they can make it to the hospital for help. Ruptured AAAs account for an estimated 15,000 deaths per year in the United States.

How is it diagnosed?

Many people discover their aneurysms incidentally when getting imaging studies for other illnesses. Because aneurysms cause no symptoms, but have such grave consequences, it is a good idea to look for them in high-risk groups. Screening and appropriate treatment are crucial to early identification and prevention of the complications of aortic aneurysm.

If you feel you might be at risk for aneurysm, the first step is to talk to your primary care provider. Upon physical examination, a physician may feel a pulsating mass in the upper abdomen. Imaging tests can aid in the detection and surveillance of AAAs. An abdominal ultrasound can confirm the presence of an aneurysm and provide information about the location and dimensions of the aorta. There are mobile screening units that provide this service in many communities and hospitals.

CTA (computed tomographic angiography) is considered the ‘gold standard’ for imaging the entire aorta. CTA is a special type of CAT scan that is performed with intravenous contrast, or dye, and can provide detailed information about the anatomic location of the aneurysm and its exact size (Figures 2 and 3). Physicians are also very interested in what branches of the aorta, including kidney or gut arteries, may be involved. Computer modeling software is used to help interpret the CTA scan and can aid physicians in fully understanding the complexity of the aneurysm.

Figure 2. An unrepaired abdominal aortic aneurysm (AAA). Computed tomographic angiography (CTA): 3-dimensional (3D) reconstruction of an unrepaired AAA measuring 5.2 cm. 3D reconstructions are helpful for planning AAA repair.
Figure 3. Endovascular repair of an abdominal aortic aneurysm (AAA). Computed tomographic angiography (CTA): 3-dimensional reconstruction of an endovascular AAA. Following endovascular repair, patients have annual CT imaging to ensure the stability and overall effectiveness of the implanted device.

Many groups, including the Society for Vascular Medicine (SVM), the Society for Vascular Surgery (SVS) and the American Heart Association (AHA), recommend a screening ultrasound for certain people at risk of AAA. The United States Preventive Services Task Force recommends a screening ultrasound for men who are aged 65–75 years and who have ever smoked. The SVS recommends a one-time screening ultrasound for all men aged 65 years and older. They also recommend screening men over 55 and women over 65 with a family history of AAA, as well as women over 65 who have smoked. Screening programs are present in many communities, but the most reliable access to aneurysm screening is through the ‘Welcome to Medicare’ physical that includes a screening ultrasound for at-risk patients.

Several studies have been done to determine when to operate on aneurysms. Because the surgery is relatively high risk, the evidence suggests that waiting until an AAA is 5–5.5 cm is the most appropriate time to consider intervention.6 In more complex aneurysms, such as those involving the thoracic (chest) or thoracoabdominal (chest and abdomen) aorta, many physicians would wait until the aneurysm is >6 cm before considering intervention because the surgery poses an even higher risk. The risk to the patient outweighs the benefit of surgical intervention in small aneurysms. Patients with small AAAs need to be closely followed by a vascular specialist and the aneurysm needs to be re-imaged over time with ultrasound or CTA studies to monitor for growth. Because aneurysm disease often occurs in patients who also have heart or lung disease, the risks of surgery include heart and lung complications.

How is it treated?

Most aneurysms are related to atherosclerosis, or plaque in the arteries. In fact, the most common cause of death in people with AAAs is not aneurysm rupture but rather other cardiovascular events such as heart attack or stroke. Thus, medical treatment for cardiovascular disease is the cornerstone of the medical treatment of AAAs. The only treatment for the aneurysm itself is surgical intervention; there is no pill or medicine that has been shown to reverse aneurysms once they have started to form. There are two different methods a surgeon or other vascular specialist might choose to treat an aneurysm (Table 2).Table 2. Comparing treatment options for abdominal aortic aneurysm.

Open repair/traditional repair
• Diseased aorta removed
• Synthetic graft sewn into place
• Hospital stay: 5–10 days
• Recovery period: 1–2 months
Endovascular aneurysm repair (EVAR)
• Stent graft relines diseased aorta
• Performed under continuous X-ray (fluoroscopy)
• Hospital stay: 2–5 days
• Shorter recovery period than open repair
• Periodic imaging studies (generally CTA or ultrasound) required for follow-up

1. Open repair/‘traditional repair’ – An incision is made in the abdomen, and the aorta is clamped above and below the diseased portion to stop blood flow. The aneurysm sac is opened and a synthetic graft (or tube) is sewn into place (Figure 1C). The average length of hospital stay following open repair is 5–10 days, with a period of observation in the intensive care unit (ICU) immediately following surgery. Potential risks and complications of open repair include bleeding, infection of the graft, surgical wound infection, heart attack, stroke, lung complications, death, and, rarely, nerve or spinal cord damage (paralysis). Another possible risk of open surgery is sexual dysfunction after surgery. Patients should discuss this issue with their physicians before surgery. The prognosis for open repair of an AAA depends on the overall health of the patient prior to surgery. Generally, patients will return to their previous daily routine within 1 or 2 months after surgery.

2.Endovascular repair (EVAR) – A stent graft is introduced into the aorta through incisions made in the patient’s groin. A stent graft is a synthetic tube that also has a stainless-steel scaffold attached to it to reline the inside of the aorta (Figure 1B). The stent graft is packed down into a delivery system and deployed between two healthy portions of aorta. This graft relines and strengthens the weakened walls of the aorta and seals off the aneurysm sac. The surgery is performed under continuous X-ray (fluoroscopy) to help the surgeon guide the stent graft to the correct location in the aorta. The average length of hospital stay is 2–5 days, and this may require a period of observation in the ICU. Potential risks and complications of endovascular repair include bleeding, infection of the stent graft, surgical wound infection, leakage of blood from the graft into the aneurysm sac, graft movement or separation of components of the graft, kidney failure, death, and, rarely, nerve or spinal cord damage (paralysis). Because this is a minimally invasive approach to aneurysm repair, many patients find the recovery to be shorter than for open surgery.

Innovations in treating complex aortic aneurysms

Endovascular repair of AAAs allows for the treatment of high-risk patients who would not be good candidates for traditional open repair. High-risk patients with heart, lung, or kidney problems would typically not do well with open repair due to the high risk of the surgery. Over the past decade, advances in surgical techniques and graft construction, in addition to carrying a lower rate of perioperative complications and death, have made EVAR a preferred choice for elective aneurysm repair.7 Current clinical research trials aim to make EVAR available to patients with more complex aortic anatomy through the development of customized stent grafts, and to increase the range of aneurysms that can be treated with commercial ‘off-the-shelf’ grafts.

Summary

Abdominal aortic aneurysm is a silent but often fatal disease. AAA is most common in older people, with both modifiable (such as smoking) and hereditary (family history of AAA) risk factors influencing disease development. Screening for AAA can aid in the early diagnosis and treatment of the disease, reducing complications and death amongst those affected. Advancements in screening techniques, surgical innovations, and graft development strive to further improve patient outcomes and disease management.

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