Definition

Abdominal aortic aneurysms (AAA) are defined as a focal dilation of the aorta of more than 50% of its expected diameter [1].

Epidemiology

AAA are:

• Found in 1% of the population over the age of 50 [2];
• Responsible for 1% of all deaths amongst Caucasian adults [3];
• The tenth leading cause of death in men over the age of 55 [4]. 

Risk factors include age, male gender, tobacco usage, family history, hypercholesterolemia, and hypertension [5].

Natural history

Aneurysms may progress in size as a result of gradual wall weakening [6], with rupture occurring at the end of the growth spectrum. Rupture risk significantly increases when AAA diameters exceed 4.5 cm in women and 5.5 cm in men [7] (Table 1).

Table 1: Annual rupture risk according to abdominal aortic aneurysm diameter.
References: Radiology, Université de Montréal, CHUM Hôpital Saint-Luc - Montreal/CA, adapted from Brewster DC et al. (2003) Guidelines for the treatment of abdominal aortic aneurysms. J Vasc Surg 37:1106-1117

A ruptured AAA has a 90% mortality rate [8]. However, hemodynamically stable patients with an impending AAA rupture can benefit from preoperative management that optimizes surgical conditions and reduces mortality rates to those comparable to elective procedures (less than 5%) [5, 9]. It is therefore crucial to identify impending AAA ruptures before rupture is completed.

Imaging findings

Imaging findings of AAA rupture can be categorized according to their location: (1) intramural, (2) luminal, and (3) extraluminal (Table 2). Intramural signs generally indicate impending AAA rupture, whereas luminal and extraluminal signs imply complete rupture. 

Table 2: Classification of signs of impending and complete aortic aneurysm rupture according to location: intramural, luminal, and extraluminal.