Assessment of Abdominal Aortic Aneurysm Risk: Asymmetry as an Additional Diagnostic Tool?

An abdominal aortic aneurysm (AAA) can be defined as a permanent and irreversible localised dilation of the infrarenal aorta. This localised dilation is a result of a degradation of the elastic media of the arterial wall. This degradation of the aortic wall can be attributed to risk factors such as tobacco smoking, sex, age, hypertension, chronic obstructive pulmonary disease, hyperlipidaemia, and family history of the disorder [1]. With the recent advancements in medicine, more AAAs are being detected than ever. Approximately 500,000 new cases are diagnosed each year worldwide resulting in 15,000 deaths per year in the USA alone [2]. Currently, the rupture risk of AAAs is regarded as a continuous function of aneurysm size, with surgical intervention decided based on the maximum diameter of the AAA. Most AAA repairs are performed when the diameter exceeds 50–60mm. It has been shown that maximum diameter may not be a reliable predictor of rupture, as smaller AAAs can also rupture. It is believed by many researchers that there is a need to review the determination of the timing of surgical intervention based solely on aneurysm diameter, and include other relevant risk factors. These additional risk factors could, for example, include, AAA wall stress, AAA expansion rate, degree of asymmetry, presence of intraluminal thrombus (ILT), and hypertension. The addition of these parameters may aid the surgical decision-making process. Shifting the current trend towards more encompassing assessment of AAA rupture potential may help reduce the morbidity and mortality rates associated with AAA repair. It was previously reported [3] that 82% of AAA ruptures occur on the posterior wall. In this research, the asymmetry of the AAA is examined, with respect to both peak wall stress and posterior wall stress, in ten realistic cases, and a resulting threshold factor is presented.