Abdominal aortic aneurysm overview

Abdominal Aortic Aneurysm Microchapters
Home
Patient Information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Abdominal Aortic Aneurysm from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural History, Complications and Prognosis
Diagnosis
Diagnostic Study of Choice
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
X-ray
Echocardiography and Ultrasound
CT scan
MRI
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Primary Prevention
Secondary Prevention
Case Studies
Case #1
Abdominal aortic aneurysm overview On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Abdominal aortic aneurysm overview
CDC on Abdominal aortic aneurysm overview
Abdominal aortic aneurysm overview in the news
Blogs on Abdominal aortic aneurysm overview
Directions to Hospitals Treating Abdominal aortic aneurysm overview
Risk calculators and risk factors for Abdominal aortic aneurysm overview

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

Abdominal aortic aneurysm, also written as AAA and often pronounced 'triple-A', is a localized dilatation of the abdominal aorta, that exceeds the normal diameter of the abdominal aorta by more than 50%.

Historical Perspective

The etymology of the word aneurysm comes from the Greek word for "dilatation". Abdominal aortic aneurysm as a medical condition has been recognized since ancient times, but was not been successfully treated until the early part of the 20th century.

Definition

The normal diameter of one's aorta depends on the patient's age, sex, height, weight, race, body surface area, and baseline blood pressure. On average, the normal diameter of the infrarenal aorta (where abdominal aortic aneurysms are located) is 2 cm. Therefore an abdominal aortic aneurysm is defined as a dilation of 3.0 cm or more.

An abdominal aortic aneurysm is to be distinguished from aortic ectasia which is defined as a mild generalized dilatation (<50% of the normal diameter of ≤ 2.9 cm) that is due to age-related degenerative changes in vessel wall.

Anatomy

A plate from Gray's Anatomy with yellow lines depicting the most common infrarenal location of the AAA.

The aorta below the renal arteries, also known as the infrarenal aorta, is the location of 90% of abdominal aortic aneurysms. Other possible locations are suprarenal and pararenal. The aneurysm can extend to include one or both of the iliac arteries.

Classification

Aneurysms are usually classified by their shape:

Fusiform Aneurysms

• Most common type seen in the infrarenal aorta
• Diffuse, circumferential

Saccular Aneurysms

• Involve only a portion of the circumference, with a characteristic outpouching of the vessel wall.

Pathophysiology

The underlying pathophysiology of abdominal aortic aneurysm involves genetic influences, smoking, hypertension, hemodynamic influences and underlying atherosclerosis. In rare instances infection, arteritis, and connective tissue disorders may play a role.

Causes

Common contributors to the pathophysiology of abdominal aortic aneurysm include atherosclerosis, hypertension and smoking.

Differentiating Abdominal Aortic Aneurysm from other Disorders

An abdominal aortic aneurysm should be differentiated from other causes of abdominal pain such as acute cholecystitis.

Epidemiology and Demographics

Abdominal aortic aneurysm is the 13th leading cause of death in the US. Abdominal aortic aneurysms are more common in developed countries. Elderly, caucasian males who are smokers are at higher risk for developing an abdominal aortic aneurysm.

Risk Factors

Abdominal Aortic Aneurysm Development

The most significant modifiable risk factor for the development of an abdominal aortic aneurysm is smoking which increases the risk of aneurysm development 8 fold. Advanced age and family history are the strongest non-modifiable risk factors for the development of an abdominal aortic aneurysm. Hypercholesterolemia and hypertension are risk factors as well. Both diabetes mellitus and black race appear to be associated with a lower incidence of abdominal aortic aneurysm.

Abdominal Aortic Aneurysm Expansion

An increased rate of expansion of abdominal aortic aneurysm is related to systolic hypertension, wide pulse pressure, and ongoing smoking.

Abdominal Aortic Aneurysm Rupture

The risk of abdominal aortic aneurysm rupture is proportional to the size and rate of growth of the aneurysm. Abdominal aortic aneurysms greater than 5 cm diameter or those that grow faster than 1 cm per year have a significantly increased risk of rupture and are indications for elective operative repair. Advanced age, female gender, hypertension, active smoking, outpouchings, and mural thrombus are also risk factors for abdominal aortic aneurysm rupture.

Screening

Approximately 16% of large abdominal aortic aneurysms (diameter > 5.5 cm) rupture, causing 9,000 AAA-related deaths in the United States per year Several studies have shown that screening can drastically reduce the aneurysm rupture rate by 45-49% for men older than 60, and reduce AAA-related mortality by 21-68%. In a landmark study randomizing 67,800 men, (The Multicenter Aneurysm Screening Study) aneurysm-related mortality was 53% lower in the screening group as compared with control patients. The United States Preventive Services Task Force (USPSTF) recommends one-time screening for abdominal aortic aneurysm (AAA) by ultrasonography in any man aged 65 to 75 who has ever smoked. The USPSTF makes no recommendation for or against screening for AAA in men aged 65 to 75 who have never smoked. The USPSTF recommends against routine screening for AAA in women.

Natural History, Complications and Prognosis

Abdominal aortic aneurysms expand slowly over time. An aortic aneurysm can progress to a ruptured abdominal aortic aneurysm, which is a medical emergency associated with an extremely high mortality. Serious complications can also occur as a result of an aortic dissection, such as myocardial infarction, shock, stroke, kidney failure, and arterial emboli. A ruptured AAA carries an overall mortality rate approaching 75%, which is much higher than the mortality rate of 2-6% in those patients who underwent elective surgical repair. Approximately 16% of large AAAs (diameter >5.5 cm) rupture, causing 9,000 AAA-related deaths in the United States per year Several studies have shown that screening can drastically reduce the aneurysm rupture rate by 45-49% for men older than 60, and reduce AAA-related mortality by 21-68%. The outcome is usually good if an experienced surgeon repairs the aneurysm before it ruptures. Rupture of an abdominal aortic aneurysm is associated with a 60% to 90% mortality before the patient reaches hospital. It is associated with a 30% to 80% operative mortality among those patients who survive long enough to undergo surgery.

Complications

When an abdominal aortic aneurysm ruptures, it is a true medical emergency. Aortic dissection occurs when the innermost lining of the artery tears and blood leaks into the wall of the artery. This most commonly occurs in the aorta within the chest. Complications include:

• Acute aortic occlusion
• Aortocaval or aortoduodenal fistulae
• Arterial embolism
• Disseminated intravascular coagulation
• Heart attack
• Hypovolemic shock
• Kidney failure
• Stroke

Prognosis

Elective Surgery in the Absence of Abdominal Aortic Aneurysm Rupture

The outcome is usually good if an experienced surgeon repairs the aneurysm before it ruptures.

Emergency Surgery in the Setting of Abdominal Aortic Aneurysm Rupture

Rupture of an abdominal aortic aneurysm is associated with a 60% to 90% mortality before the patient reaches hospital. It is associated with a 30% to 80% operative mortality among those patients who survive long enough to undergo surgery.

History

Given that smoking increases the risk of abdominal aortic aneurysm development, a smoking history should be obtained in elderly men. If a male over the age of 65 has a history of smoking, they should undergo ultrasonography to screen for an abdominal aortic aneurysm.

Symptoms

The vast majority of aneurysms are asymptomatic. Spontaneous abdominal pain in a patient with a pulsatile epigastric mass or a known AAA may signal rupture into the retroperitoneum or leakage within the aneurysm wall. If a patient does develop symptoms, the risk of rupture is quite high, which is why symptoms are considered an indication for surgery.

Possible symptoms include:

• Low back pain
• Flank pain
• Abdominal pain
• Groin pain
• Pulsating abdominal mass
• Peripheral embolization is rare with abdominal aortic aneurysms in contrast to popliteal artery aneurysms in which distal embolization is common.

Physical Examination

Physical examination has a low sensitivity in the detection of small abdominal aortic aneurysms (29-61% for abdominal aortic aneurysms 3.0-3.9 cm in diameter) but has a sensitivity of 76-82% to detect those abdominal aortic aneurysms that are 5.0 cm or larger that may warrant repair. It is easier to detect a pulsatile mass in thin patients and those who do not have tense abdomens. Contrary to popular belief, gentle palpation of abdominal aortic aneurysms is safe, and does not precipitate rupture.

Abdominal Ultrasound

Abdominal ultrasound is the imaging modality of choice to detect and follow the progression of an abdominal aortic aneurysm. It has a sensitivity that is close to 100%. Ultrasound also detects the presence of mural thrombus and iliac artery aneurysms. Patients should fast before examination to optimize image quality.

Abdominal X-Ray

Up to 50% of AAAs can be recognized on plain roentgenograms as a calcified aneurysmal wall.

Computed Tomography (CT)

Although CT scanning provides detailed anatomic information and is valuable in planning abdominal aortic aneurysm repair, it is not used as a screening tool given the potential nephrotoxicity associated with the dye load, the cost, and the exposure to radiation.

Magnetic Resonance Imaging (MRI)

Although MRI does not require nephrotoxic contrast, it is less accurate than thin-slice CT. It is also costly, and is not as readily available as contrast CT and ultrasonography.

Prevention

Smoking cessation and blood pressure management are two strategies to reverse modifiable risk factors for the development of, progression of, and rupture of an abdominal aortic aneurysm.

Medical Therapy

Risk factor modification including smoking cessation, management of hypertension, and lipid lowering are essential in reducing the risk of development and the rate of progression of abdominal aortic aneurysms.

Surgery

Indications for operative repair of an abdominal aortic aneurysm include the presence of symptoms such as back pain, the presence of a rupture or contained rupture, an abdominal aortic aneurysm diameter greater than 5.5 cm, a rate of expansion of greater than 1 cm in one year, and an inflammatory or infectious etiology. Open surgical repair is favored in young patients as an elective procedure, the presence of an expanding aneurysm, symptomatic aneurysm, or ruptured aneurysm. An endovascular repair (EVAR) is favored in older patients and high risk patients or those unfit for open repair. Risk factors for postoperative morbidity and mortality include extensive atheromatous disease, mural calcification, thrombosis, juxtarenal extension of the aneurysm and the presence of inflammatory changes.