What is an Abdominal Aortic Aneurysm?
An aneurysm is an abnormal dilatation of a blood vessel. The commonest site to develop an aneurysm is the aorta, at the back of the abdomen just below the kidneys. This is called the infrarenal aorta and an aneurysm in this area is called an abdominal aortic aneurysm and often referred to as an AAA.
AAAs gradually grow at a rate of around 1 to 5 mm per year. The bigger they get, the more likely they are to burst. Ruptured AAA is a common cause of sudden death. Males are 8 times more the faster the grow, & likely to be affected than females, and 1 in 20 men over the age of 65 have an AAA. However females with an aneurysm are more prone to rupture than their male counterparts.
Why do Aneurysms Develop?
The main risk factors for developing an aortic aneurysm are age, male gender, smoking and family history. The aneurysm wall becomes inflamed and the normal cells and proteins which make up the artery wall break down and weaken. The risk of rupture rises sharply once the aneurysm diameter exceeds 6cm, therefore repair is advised for aneurysms over 5.5cm in all but very unfit patients. Most AAAs are asymptomatic until they burst. Screening programs reduce deaths due to aneurysm rupture. Many AAAs are detected by accident during tests for other problems.
How are AAAs diagnosed?
Physical examination is unreliable to detect and measure AAAs. Ultrasound is highly accurate, and is used to diagnose and monitor aneurysm growth. Once an aneurysm had reached 5.5cm and repair is required, CT scanning is vital to define aneurysm anatomy and determine how best to repair it.
There are two ways to repair an abdominal aortic aneurysm: open repair and endovascular (key-hole) repair using a stent-graft.
Open Aneurysm Repair
Open repair comprises replacement of the aneurysmal aorta with an artificial graft sutured into place just below the renal arteries. This is a major abdominal operation with significant risks involved. The risk depends on the extent of the aneurysm, and the age and fitness of the patient. Despite these concerns, the long term outlook after open repair is good and open aortic reconstruction is a very durable procedure that lasts for years without further intervention.
Endovascular aneurysm repair
Endovascular Aneurysm Repair (EVAR) allows a stent-graft to be delivered inside the aneurysm via the femoral artery, then expanded and fixed in position under Xray guidance. The whole procedure can be achieved via small groin incisions. Recovery is much quicker than for open repair and less fit patients can be treated. The risk of severe complications is also much lower. Endovascular repair can be used for planned and emergency operations where the aneurysm has already ruptured. Blood loss is much lower and transfusion less likely to be required.
Complex endovascular aneurysm repair (fenestrated and branched stent-grafts)
Not all patients are suitable for endovascular repair. The shape and extent of the aneurysm mean some patients will require open surgery rather than a key-hole operation. Advances in stent-graft technology however are increasing the proportion of patients who can receive minimally invasive treatment. For example, fenestrated stent-grafts allow aneurysms which extend very close to the kidneys to receive key-hole surgery. Similarly, branched stent-graft devices allow treatment of aneurysms that extend deep into the pelvis involving arteries which supply the pelvic organs. Until recently, many such patients would have been unsuitable for such treatment and would have had to have open surgery for their aneurysms