Screening for abdominal aortic aneurysm

INTRODUCTION

An aneurysm is a focal dilation of a blood vessel with respect to the original or adjacent artery. An abdominal aortic aneurysm (AAA) is defined as a dilated aorta with a diameter at least 1.5 times the diameter measured at the level of the renal arteries. In most individuals, the diameter of the normal abdominal aorta is approximately 2.0 cm (range 1.4 to 3.0 cm). For practical purposes, an AAA is diagnosed when the aortic diameter exceeds 3.0 cm [1,2].

The majority of aneurysms never rupture, but when they do, sudden death from retroperitoneal or intraperitoneal exsanguination is usual unless surgery is performed immediately. Acute AAA rupture is one of the most dramatic emergencies in medicine, particularly because it often masquerades as another problem. In the United States, ruptured AAA is estimated to cause 4 to 5 percent of sudden deaths and is the thirteenth most common cause of death [3].

The increasing use of computed tomography and magnetic resonance imaging has revealed asymptomatic and previously undiagnosed AAAs. The concern raised by people who become incidentally aware of a "ticking bomb" in their abdomen presents a common dilemma to clinicians. The decision to perform elective surgery to prevent aneurysm rupture must be weighed against immediate surgical risks in an often older adult population and the low likelihood that a rupture will occur before death from other causes [4]. The trade-off between present and future risk should involve patient preference as an important consideration in the decision to screen for an AAA. (See "Management of asymptomatic abdominal aortic aneurysm", section on 'Introduction' and "Management of asymptomatic abdominal aortic aneurysm".)

The dilemmas associated with the incidental discovery of an AAA make decisions regarding screening difficult. Systematic population screening would yield many previously undiagnosed small aneurysms that are unlikely to rupture, resulting in needless disease labeling [5]. Only aneurysms of a certain size would be considered for surgery, with smaller aneurysms subject to watchful waiting.

Issues related to screening for AAAs will be reviewed here. Details regarding the clinical manifestations, diagnosis, and treatment of AAAs are presented separately. (See "Clinical features and diagnosis of abdominal aortic aneurysm" and "Management of asymptomatic abdominal aortic aneurysm", section on 'Introduction'.)