Abdominal Aortic Aneurysm (AAA)
An aneurysm is an abnormal dilatation of a vessel resulting in a ballooning out and weakening of the arterial wall. Aneurysms can potentially occur in any location, however, they tend to affect arteries in a few specific locations such as the abdominal aorta, the popliteal arteries behind the knee and as berry aneurysms in the brain.
The aorta is the main artery of the body carrying blood from the heart to the rest of the body. For some reason, possibly due to flow dynamics it seems to be predisposed to aneurysm formation between the main branches to the kidneys and where it divides to each leg. This is roughly at the level of the naval or belly-button.Usually,it’s diameter is about the size of a 25mm hose and as you can imagine the blood contained within is under a fair bit of pressure, 120-150 mmHg or 2-5 PSI to be precise. As a result of degenerative changes in the elastic and collagen fibers of the aortic wall the aneurysm slowly increases in size. Once it reaches a size of 5 cm or more there is a real risk of the aneurysm splitting and rupturing with catastrophic results. Abdominal aortic aneurysms are a bit like a silent time-bomb waiting to go off, if it does, the mortality is about 90%; if you’re lucky enough to reach hospital your chances of survival are about 50-60%. Below is what a ruptured aneurysm looks like during an emergency op to repair it. You can clearly see the where the blood has leaked out from the aorta. They are often much worse than this with much of the patient’s blood volume in the wrong place. (photo courtesy of St Richard’s Hospital, Chichester)
AAA’s appear to be more common in men over the age of 65 and again smoking, high blood pressure and cholesterol are often to blame. Because of the high mortality with rupture, vascular surgeons are keen to repair AAA’s before they burst. The traditional approach to this is to perform an operation to replace the diseased segment of aorta with a polyester graft ( essentially a piece of synthetic hose). This durable procedure has been around since the 1950′s and has stood the test of time, however, the operation is fairly major with a significant risk of complications and death. Most of our patients are not particularly fit and have concurrent medical conditions such as heart disease, diabetes or emphysema (bad lungs).
More recently, we are now repairing AAA’s using endovascular (EVAR) techniques. This involves reinforcing the aneurysm from within using a metal framework or stent covered with polyester rather like re-lining a chimney. The endovascular device is inserted into the AAA via the femoral artery under X-ray control and therefore is a much lesser procedure than an open operation. The drawback however, is that the device requires long term follow up to ensure that it remains in position and does not leak causing re-pressurisation of the AAA. Furthermore, not all aneurysms are suitable for this procedure due to anatomical constraints and the patient may still require the traditional open operation. Below you can see a CT reconstruction of a AAA that has undergone an endovascular repair or EVAR. The stent is made from a special alloy called Nitonol so there is no danger of it rusting!!