Abdominal Aortic Aneurysm

An abdominal aortic aneurysm (AAA) is a localized dilatation of the abdominal aorta, most commonly the infrarenal segment. It is the most frequent aortic aneurysm and is usually asymptomatic, growing slowly until it is detected on imaging or, less often, presents with rupture. Rupture is the central danger and carries very high mortality, which is why diameter-based surveillance and screening of higher-risk groups are central to how the condition is approached (Sakalihasan et al., 2005).

Definition

An abdominal aortic aneurysm is a permanent localized dilatation of the abdominal aorta, conventionally defined as an infrarenal diameter of 3.0 cm or greater, or at least 1.5 times the expected normal diameter.

Scope

This topic covers the definition, location, mechanisms, risk factors, natural history, and screening rationale of abdominal aortic aneurysm. It summarises how aortic diameter and growth are used as risk surrogates and how population screening has been studied. It is reference-educational and does not provide individualized management or operative recommendations.

Key concepts

• Infrarenal location
• Diameter threshold (>= 3.0 cm)
• Wall degeneration and proteolysis
• Smoking, age, and male sex as risk factors
• Growth rate and rupture risk
• Population screening
• Surveillance imaging

Mechanisms

AAA develops through chronic degeneration of the aortic wall, with breakdown of elastin and collagen by proteolytic enzymes, inflammation, and smooth-muscle loss in the media, leaving the wall weaker and prone to progressive dilatation. As diameter grows, wall stress increases with the radius (Laplace's law), so larger aneurysms tend to expand faster and carry higher rupture risk. Atherosclerosis frequently coexists, and smoking is the strongest modifiable association, while a minority of cases reflect inflammatory or heritable processes (Sakalihasan et al., 2005; Wanhainen et al., 2019).

Clinical relevance

AAA is a reference example of how an asymptomatic, slowly enlarging vascular lesion is detected and monitored using size criteria, and of how population screening is justified. Guideline statements describe how diameter, growth rate, and patient factors inform surveillance and the threshold for considering repair; these descriptions characterise the evidence base and are not a substitute for individualized clinical assessment (Wanhainen et al., 2019; Isselbacher et al., 2022).

Epidemiology

AAA is strongly associated with increasing age, male sex, smoking, and a family history of the condition, with smoking being the dominant modifiable risk factor. Because most aneurysms are silent until rupture, several countries have studied or implemented ultrasound screening of older men, the group with the highest yield, and screening programmes have informed the rationale for early detection (Sakalihasan et al., 2005; Wanhainen et al., 2019).

History

Surgical repair of the abdominal aorta was established in the mid-twentieth century, and the later development of endovascular aneurysm repair broadened treatment options. Randomised trials of screening and of surveillance versus early repair, together with successive vascular-surgery guidelines, consolidated the diameter-based framework now used to describe and follow the disease (Sakalihasan et al., 2005; Wanhainen et al., 2019).

Debates

At what diameter and growth rate should repair be considered?

Because rupture risk rises with size but repair also carries risk, the threshold for intervention balances aneurysm diameter, growth rate, sex, and patient fitness rather than a single cutoff, and the precise thresholds continue to be refined by evidence.

Who should be screened for AAA?

The yield and cost-effectiveness of one-time ultrasound screening are highest in older men with a smoking history, and how broadly screening should extend to women and other groups remains a question informed by trial and registry data.

Seminal works

• sakalihasan-2005
• wanhainen-2019
• isselbacher-2022

Frequently asked questions

When is the abdominal aorta considered aneurysmal?

It is conventionally called an aneurysm when the infrarenal diameter reaches about 3.0 cm or greater, or roughly 1.5 times the expected normal width for that person.

Why is screening offered mainly to older men who have smoked?

AAA is usually silent until rupture, and its risk is concentrated in older men with a smoking history, so one-time ultrasound screening of that group has the greatest yield in studies.