Abdominal aortic aneurysms

90% of aortic aneurysms affect the infra-renal abdominal aorta, 8% the thoracic aorta and 2% both (thoraco-abdominal). If the aneurysm is operated on before rupture, the mortality should be 5% or less. Following rupture, it is thought that well over 50% of patients die, frequently undiagnosed, before arrival in hospital and the mortality of those receiving an operation approaches 50%.

Asymptomatic AAA

Ultrasound screening studies have shown an incidence of 5% in males aged 65-74, four times > that in females. A single ultrasound scan at the age of 65 in males is a cost effective tool for detecting asymptomatic AAA and arrangements are underway for a national screening programme.

Large studies have concluded that small infra-renal AAAs, less than 5.5 cm in antero-posterior diameter as measured on ultrasound, can safely be entered into a surveillance programme of 6-monthly repeat ultrasounds. As long as they remain asymptomatic and expand slowly (<0.5 cm in 6 months) they carry an annual rupture rate of 1%. Aneurysms >5.5 cm carry an annual rupture rate of about 10% which increases with aneurysm size and this is an indication for aneurysm repair if the patient is fit for surgery.

Symptomatic AAA

Symptoms of abdominal or back pain, which may radiate to the groin, or tenderness on palpating an aneurysm should be taken as a predictor of imminent rupture and repair should be undertaken as soon as possible. The differential diagnosis includes:

• osteoporotic vertebral collapse,

• renal or ureteric pain,

• pancreatitis,

• perforated duodenal ulcer,

myocardial infarction.

Ruptured AAA

This surgical emergency should be suspected in anyone with abdominal or back pain and collapse. A pulsatile mass can usually, but not always, be palpated. If the diagnosis is obvious then immediate surgical repair is indicated. CT should only be performed if there is doubt about the diagnosis and the patient is well compensated.

Open repair

The aneurysm is replaced by inserting a prosthetic graft inside the aneurysm after appropriate mobilisation and clamping of the arteries (Fig. 15.17). The graft may be a simple tube graft to above the aortic bifurcation or may extend as a 'trouser' graft distally to one or both iliac or femoral arteries. The operation carries a mortality of around 5% but returns the patient to a life expectancy equal to their age matched peers.

Figure 15.17. Gelatin-impregnated Dacron graft replacing aortic aneurysm.

Endovascular aneurysm repair (EVAR)

A covered stent graft is deployed under X-ray control via an open approach to the femoral arteries avoiding the need for aortic cross-clamping. The procedure carries a lower operative mortality but a cumulative annual 10% re-intervention rate for device failure or slippage or continued aneurysm expansion is required. Patients require annual CT surveillance. Long team outcomes for EVAR are as yet unknown. EVAR confers to survival benefit over conservative management in patients unfit for open surgery.

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