Abominal Aortic Aneurysm
An abdominal aortic aneurysm (AAA) is a swelling of the artery caused by weakness in the artery wall which develops over many years. Definitions vary but in general a localised swelling of the aorta greater than 3cm is regarded as an aneurysm. The normal aorta is 2-2.5cm in size. Aneurysms can be found in other arteries but the abdominal aorta is the commonest.
They are associated with disease of the arteries (atherosclerosis) high blood pressure and smoking. They are 9 times more common in men than women and about 5% of men over the age of 80 will have one. The rate increases when a family member has one indicating that there is a genetic predisposition although no specific genes have been identified.
AAAs are usually asymptomatic and are found incidentally when being examined by a doctor (although often difficult to detect this way) or investigated for some other abdominal problem. In some countries screening with ultrasound is carried out on all men 65 or over.
Aneurysms are important because they can rupture as the first symptom. This is an often fatal event with major internal bleeding. Many do not make it to hospital and of those that do only 50% may survive. The risk of rupture varies with size. In AAAs less than 5.5cm the risk is about 1% per year and if over 6cm about 15% per year. There is evidence that this risk in women is 2-3 times greater.
There is some evidence that aneurysm growth slows with risk factor management. This would consist of smoking cessation, good blood pressure control and cholesterol lowering medication. Aneurysm growth can be carefully monitored with regular ultrasound scanning such that when the growth rate is high (greater than 1cm in one year) or it reaches the threshold for treatment it can be repaired in a timely fashion.
Because of the consequences of rupture it is best to repair the AAA before this happens. AAA over 5.5cm in men (5.0cm in women) are commonly repaired as a planned procedure to reduce the risk of this complication.
There are 2 ways to approach repair of the aorta in this situation. They are described as open or traditional repair versus endovascular (EVAR) or stent repair.
Open repair involves a large cut in the abdomen with replacement of the diseased artery with a synthetic tube sewn in place permanently with stitches. This operation has been tried and tested now for almost 60 years and is very effective and durable. You would expect to be in hospital for 5-10 days with further recovery required at home. The operation is major and has about a 5% risk of dying associated with it.
Endovascular repair does not require a cut in the abdomen but does require cuts in the groins so that a device can be place inside the aorta under x-ray control. This technique has been in use for about 20 years and has undergone considerable development in this time. Only about 60% of aneurysms are deemed suitable for this procedure. There is a lower risk associated with this approach with a 2% risk of dying. The drawback with the procedure is the need for on-going surveillance by ultrasound and CT scan. Up to 30% of patients will require further invasive x-ray guided procedures to keep the stent working normally.
There are many things to discuss and consider when the diagnosis of AAA is made. Largely the difficulty is coming to terms with the need for major surgery when you may feel otherwise unaffected by it.