An abdominal aortic aneurysm is a localized enlargement of the abdominal aorta. When the diameter is greater than 3 cm or more than 50% larger than normal, this is considered aneurysmal. Abdominal aortic aneurysms (AAA) are not rare and are common in men over the age of 65, especially those who have peripheral vascular disease.,,
While a small abdominal aortic aneurysm may not enlarge over time, all aneurysms over 5 cm have the potential to rupture. A vascular surgeon should evaluate these patients immediately. Aneurysms between 3 cm and 5 cm can be managed expectantly unless the patient is symptomatic. Most individuals with this type of aneurysm also have peripheral vascular disease. Abdominal aortic aneurysms occur due to degeneration of the media with progressive enlargement of the vessel lumen. Risk factors for this condition include:
With the increased use of ultrasound, the diagnosis of abdominal aortic aneurysms is quite common. They tend to be more common in smokers and elderly white males. Based on autopsy studies, the frequency of these aneurysms varies from 0.5% to 3%. The incidence of abdominal aortic aneurysms increases after age 60 and peaks in the seventh and eighth decades of life. White men have the highest risk of developing abdominal aortic aneurysms. They are uncommon in Asian, African American, and Hispanic individuals.
Abdominal aortic aneurysms tend to occur when there is a failure of the structural proteins of the aorta. What causes these proteins to fail is not known, but it results in the gradual weakening of the aortic wall. Autopsy studies usually show marked degeneration of the media. Other factors that may play a role in the development of these aneurysms include genetics, marked inflammation, and proteolytic degradation of the connective tissue in the aortic wall.
Examination of resected abdominal aortic aneurysms usually reveals a state of chronic inflammation with an infiltrate of neutrophils, macrophages, and lymphocytes. The media is often thin, and there is evidence of degeneration of the connective tissue.
The majority of abdominal aortic aneurysms are identified incidentally during an examination for another unrelated pathology. Most individuals are asymptomatic. Palpation of the abdomen usually reveals a pulsatile abdominal mass which is not tender. Some patients present with rupture of an abdominal aortic aneurysm, and this can be life-threatening. These patients present in shock with diffuse abdominal pain and distension. However, the presentation of patients with this type of ruptured aneurysm can vary from subtle to quite dramatic. Most patients with a ruptured abdominal aortic aneurysm die before hospital arrival.
The diagnosis of an abdominal aortic aneurysm is usually made with ultrasound, but a CT scan is needed to determine the exact location, size, and involvement of other vessels. Most of these aneurysms are located below the origin of the renal arteries. They may be classified as saccular (localized) or fusiform (circumferential). Some people may develop an inflammatory abdominal aortic aneurism which is characterized by intense inflammation, a thickened peel, and adhesions to adjacent structures. Angiography is now rarely done to make the diagnosis because of the superior images obtained with CT scans.
The treatment of unruptured abdominal aortic aneurysm has changed over time. Treatment is recommended when it reaches 5 cm to 5.5 cm. In the past, these aneurysms were repaired through invasive, open surgery. With advances in endovascular techniques, many are now repaired with a stent placed via the femoral arteries. Endovascular therapy is recommended in patients who are not candidates for open surgery. This includes patients with severe heart disease, active infection, and other comorbidities that preclude open repair. A ruptured abdominal aortic aneurysm always requires surgery, but the mortality rates remain high. The risk of surgery is influenced by the age of the patient, the presence of renal failure, and the status of the cardiopulmonary system.,
Data show that for unruptured abdominal aortic aneurysms, endovascular repair has no long-term differences compared to open repair. All patients with small abdominal aortic aneurysms who do not undergo repair need periodic follow up with an ultrasound every 6 to 12 months to ensure that the aneurysm is not expanding.
Once an abdominal aortic aneurysm ruptures, the prognosis is grim. More than 50% of patients die before they reach the emergency room. Those who survive have very high morbidity and never recover their previous state. For those undergoing elective repair, the prognosis is good to excellent. However, long-term survival depends on other comorbidities like chronic obstructive pulmonary disease, heart disease, and peripheral vascular disease.
After repair, it is essential that the patient discontinue smoking, eat a healthy diet, and maintain a healthy weight.
Once an abdominal aortic aneurysm is diagnosed, the patient should be referred to a vascular surgeon. If the aneurysm is less than 3 cm, then annual follow up with ultrasound is recommended.
To ensure that the patient is fit for surgery, a consult with the cardiologist and pulmonologist is recommended.
In patients with an abdominal aortic aneurysm smaller than 4.5 cm, discontinuation of smoking is recommended to lower rupture risk. Hypertension should be managed aggressively with beta-blockers which are known to reduce stress on the aortic wall.
Individuals with an abdominal aortic aneurysm smaller than 3 cm do not need further follow up. For those with one between 3 cm to 4 cm, a yearly ultrasound is recommended. An abdominal aortic aneurysm between 4 cm to 5 cm should be assessed with ultrasound every six months, and if the size increases, the patient should be referred to a surgeon.
Evidence shows that patients with an abdominal aortic aneurysm between 4 cm to 5 cm benefit from elective surgery, especially those who are young. In women, an abdominal aortic aneurysm of 4.5 cm should be considered for repair because many anecdotal reports suggest that rupture can occur in these small aneurysms.
Any aneurysm that grows by one or more centimeters in 12 months should be considered for surgery.
All patients with an abdominal aortic aneurysm more than 6 cm should be referred for elective repair.
When detected in elderly patients with numerous comorbidities, this aneurysm requires discussion about the potential benefits of treatment versus rupture. In elderly patients who have a ruptured abdominal aortic aneurysm, no intervention is recommended as the morbidity of surgery is enormous; even if the patient is saved, the residual deficits make for a very poor quality of life.
Patients with malignancies who have been diagnosed with an abdominal aortic aneurysm should only be considered for surgery if they have a life expectancy of more than two years.
Contraindications for abdominal aortic aneurysm repair include:
Endovascular repair is now an established technique for repairing an abdominal aortic aneurysm. Advances in minimally invasive instruments and techniques have reduced the morbidity of the procedure. While initially, endovascular repair was only for elderly patients and those with high morbidity, today the procedure is being offered to young people who do not want to undergo the open repair.
Endovascular repair has much less morbidity than the open surgery. However, evidence continues to accumulate that it is also more likely to be associated with a secondary intervention, which increases not only costs but also the risk of complications. The two reasons for reintervention include endoleaks at the proximal aortic site and persistently elevated aneurysm sac pressure. The long-term durability of endovascular surgery remains to be determined.
All patients who elect to undergo endovascular repair should be informed of the potential complications, and the need for close follow up. Serial CT scans are required at 1, 6, and 12 months after repair to check for endoleaks.
An evidence-based approach to AAA
Abdominal aortic aneurysms are relatively common and can be life-threatening once they reach more than 7 cm. Individuals who are at the highest risk for them are usually men more than 60 years of age who smoke and have peripheral vascular disease. Because of the enormous morbidity and mortality of a ruptured abdominal aortic aneurysm, many recommendations have been made over the years. The United States Preventive Services Task Force recommends a one-time screening with ultrasound of men between the ages of 65 and 75. There is not enough evidence to recommend screening for these aneurysms in women of the same age group.,[Level V] Individuals with a stable abdominal aortic aneurysm should undergo regular surveillance or surgery depending on its size. Surgery is usually recommended when an aneurysm reaches 5.5 cm in diameter. Most abdominal aortic aneurysms are first detected in the emergency room or at the primary care provider’s clinic. It is important to involve an interprofessional group of health care workers to manage the disorder.
Once an abdominal aortic aneurysm ruptures, the prognosis is grim. More than 50% of patients die before they reach the emergency room. Those who survive have very high morbidity and never recover their previous state. For those undergoing elective repair, the prognosis is good to excellent. However, long-term survival depends on other comorbidities like chronic obstructive pulmonary disease, heart disease, and peripheral vascular disease.[Level V]