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Current management of abdominal aortic aneurysms



Abstract

The operative mortality following conventional open abdominal aortic aneurysm (AAA) repair has not fallen significantly over the past two decades. The introduction of Endo Vascular Aneurysm Repair (EVAR) in 1991 has provided and alternative to open AAA repair, and an opportunity to improve operative mortality. Since then, the treatment of AAA has undergone a revolutionary change. However, a maximum transverse measurement of >5.5 cm is still a reasonable threshold with which to recommend repair in most patients with asymptomatic AAA; repair at smaller diameters may be recommended for women and some select cases. Open repair has proven durable, and should be considered in younger and lower-risk patients, and in some complicated cases it may be the only option. Open repair and EVAR are complementing each other in the current management of AAA. The decision as to which method is the best option for each individual should be made on the basis of the specific patient. Advances in endovascular technology have strengthened the armamentarium of vascular surgeons in dealing with AAA. The aims of this article is to provide an overview on the current management of AAA, with relevance to general practice.



Introduction

AAA is a fatal condition that primarily affects older patients. The incident in Hong Kong is not as rare as it was previously thought [1]. With a progressively ageing population, the incidence and prevalence of AAA is certain to rise. Most AAAs are asymptomatic, and physical examination lacks sensitivity for detecting an aneurysm [2]. It is important that family physicians understand which patients are at risk for the development of AAA, and the appropriate evaluation once a patient has been diagnosed, with knowledge on the current treatment options of AAA.



Definition and aetiology

An aneurysm is a permanent focal dilatation of an artery to 1.5 times its normal diameter. The normal infrarenal aortic diameters in patients older than 50 years are 1.5 cm in women, and 1.7 cm in men. By convention, an infrarenal aorta 3 cm in diameter or larger is considered aneurismal [3]. The primary event in the development of an AAA involves proteolytic degradation of the extravellular matrix proteins, elastin and collagen. Various proteolytic enzymes are involved during the degradation and remodeling of the aortic wall [4]. Cigarette smoking elicits and increased inflammatory response within the aortic wall [5]. Increased biomechanical wall stress also contributes to the formation and rupture of aneurysms, with increased wall tension and disordered flow in the infrarenal aorta. Approximately 20% of first-degree relatives, predominantly men, of a patient with an AAA will develop an aneurysm [6].



Screening

In Hong Kong, there is no screening programme for AAA. However, in the US, the US Preventive Services Task Force has released a statement summarizing recommendations for screening for AAA [7]. The guideline recommends one-time screening with ultrasound for AAA in men 65-75 years of age who have ever smoked. No recommendation was made for, or against, screening in men 65-75 years of age who have never smoked, and it recommended against screening women. Men with a strong family history of AAA should be counselled about the risks and benefits of screening as the approach 65 years of age.

Ultrasound is the standard imaging tool; if performed by trained personnel, it has a sensitivity and specificity approaching 100% and 96%, respectively, for the detection of infarenal AAA [7].





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