A palpable abdominal mass

This contrast enhanced abdominal CT scan shows a large (8 cm) abdominal aortic aneurysm. Other information that would be available from scans in this series would be its relationship to the renal arteries and whether it extended into the iliac vessels. This was in fact an infra-renal aneurysm with no extension into the iliac arteries. The patient was 75 years old, the aneurysm was asymptomatic, he was medically fit and proceed to uncomplicated elective surgery.

Abdominal aortic aneurysms (AAA) have an increasing incidence in the United Kingdom where they account for approximately 10,000 deaths per year. With the limited number of post-mortems performed on those whom die suddenly in the community determining the exact incidence is impossible. It has been estimated that of those who suffer a ruptured aortic aneurysm in the community only about 50% will reach hospital alive. The 30-day mortality of those with a ruptured aneurysm who reach surgery is also approximately 50%. As a result, at best only, the chance of having short-term survival after a ruptured AAA is 1 in 4. Those who survive usually have had an enclosed retroperitoneal bleed. Intraperitoneal rupture is invariably fatal.



In contrast, the peri-operative mortality of elective aneurysm repair is less than 5%. Selection of patients for elective surgery is therefore very much a matter of assessing the relative risks of surgery against the risks of aneurysm rupture. In general those with symptomatic aneurysms, irrespective of their size, should be offered surgery if medically fit for an operation. The selection of those with asymptomatic aneurysms is more controversial. The risk of aneurysm rupture is related to aortic diameter. Most surgeons would offer surgery to those with an aortic diameter greater than 6 cm. Most would observe with serial ultrasound assessment those with a diameter less than 4 cm. The management of those with a diameter between 4-5.5 cm has been addressed in the recently published UK Small Aneurysm Trial in which 1000 patients were randomised to operation or surveillance. This showed no survival advantage for those patients offered early operation

Most post-operative deaths in those undergoing elective surgery result from acute cardiac events. As a result patient pre-operative assessment is vital. Atherosclerosis is a systemic disease and careful assessment of the remainder of the vascular tree is essential. In particular, those with ischaemic heart disease may benefit from a cardiological assessment and investigation with nuclear medicine cardiac perfusion scans. It has been suggested that 10% of patients may benefit from cardiac catheterisation with a view to coronary revascularisation before AAA surgery.

Screening for AAA is a current area of interest. The population prevalence of small AAA has been estimated to be 3-8%. There is no doubt that elective aneurysm surgery reduces the mortality of aneurysm rupture. On the other hand patients with AAA are usually elderly with other significant co-morbid pathology. There is no consensus as to whether population screening will be cost-effective. It may be that a selective screening policy of high risk individuals (males, hypertensive) may be the way forward. It has been estimated that a one-off ultrasound scan of all males at 65 years would identify 90% of the population at risk of developing an AAA.

Recent interest has been shown in the rapidly evolving techniques of endovascular repair of AAA. The attractions of this technique is that it may be applicable to those considered unfit for conventional surgery. It also avoids the complications of intra-abdominal surgery, the haemodynamic effects of aortic cross-clamping and the ischaemia-reperfusion complications after unclamping. In this technique a collapsed stent is introduced through a peripheral vessel usually the femoral artery. It is positioned under radiological guidance and then deployed. The self expanding stent is anchored above and below the aneurysm excluding the sac from the circulation. The technique is not without complications but early results have been encouraging. With improved stent design the results of future studies are awaited with interest