Abdominal aortic aneurysm (AAA) is defined as an abnormal dilatation of the abdominal aorta with a diameter greater than 3 cm.
It is a relatively common aortic pathology that results in significant amounts of morbidity and mortality. Between 1-2% of men undergoing NHS screening (over the age of 65) will be found to have a AAA. The vast majority are infrarenal (i.e below the origin of the renal arteries).
AAA may be considered a degenerative condition of the aorta though its aetiology is not fully understood.
A number of risk factors have been shown to be associated with AAA:
Uncommonly an aneurysm may be secondary to infection, inflammatory diseases or trauma.
AAA’s are frequently asymptomatic, the presence of symptoms often indicates rupture or impending rupture.
Unruptured AAA’s tend to be asymptomatic. Local mass effect may result in back pain or ureteric obstruction. AAA may be found incidentally on imaging or clinical examination. It may also present due to complications such as distal embolisation.
Ruptured AAA's frequently present with pain, the patient may also exhibit signs of haemodynamic compromise.
The NHS has introduced screening for AAA for men aged 65 and over in England. It consists of an abdominal USS.
USS is a relatively cheap, non-invasive test with a high sensitivity for detecting AAA. Further management is dependent on the USS findings:
Screening is also indicated outside these groups if the patient is at greater risk of a AAA than the general population (e.g. family history). In the latest NICE guidance they advise considering USS in women over 70 (who have not already had abdominal imaging) with any one of; COPD, vascular disease, family history, hyperlipidaemia, hypertension, smoker/ex-smoker.
AAA may be diagnosed with an abdominal USS or axial imaging.
Management of AAA depends on the patients presentation, co-morbidities and anatomical considerations.
Patients with stable AAA not requiring surgical input should be advised to follow a healthy lifestyle and diet. They should be evaluated for hyperlipidaemia and hypertension and treated if necessary. Help with smoking cessation should be offered.
Their AAA should be monitored based on its diameter (see screening chapter above).
Open surgical repair has long been the main-stay of management of patients with AAA. Elective surgery is indicated in:
EVAR is a minimally invasive technique that utilises endovascular iliofemoral access to deploy an aortic graft. It may be used either in the elective or emergency setting.
The latest NICE guidance outlines when to consider EVAR - it is quite complex(!) and well worth a read if you are interested. We will summarise a number of the key points.
NOTE: A standard EVAR is one that uses a standard infrarenal device, follows manufacturers guidance without any adjunctive procedures. Anything else is considered complex.
Acute rupture represents a medical emergency.
Fluid resuscitation / blood transfusion (BP targets vary, many advocate 100-120 systolic) and analgesia are key. Emergency surgery or EVAR may be indicated in suitable patients in acute rupture.
The management of a ruptured AAA is complex and dependent on numerous factors, we will broadly outline some of the options and considerations advised by NICE.
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