Abdominal aortic aneurysm

An abdominal aortic aneurysm is the most common form of aortic aneurysm, the other being thoracic aortic aneurysm. They may be infrarenal (most common) or suprarenal. They usually start below the renal arteries and end above the iliac bifurcation. They can be saccular or fusiform, often with atherosclerotic plaques and large mural thrombi. AAA are usually asymptomatic until they rupture, at which point they are rapidly deadly and have a terrible prognosis. The mortality is 80%, and only 50% ever reach the hospital alive. Anterior ruptures into the abdominal cavity have the highest mortality and rarely reach the hospital alive. Posterior ruptures into the retroperitoneum limits bleeding somewhat, having a lower mortality.

AAA is a disease of elderly men, especially smokers.

It's important to screen for and monitor abdominal aortic aneurysms to reduce the incidence of rupture.

Etiology

See aortic aneurysm.

Clinical features

Non-ruptured abdominal aortic aneurysm (AAA) is asymptomatic. They may be discovered incidentally, during screening, or on routine physical examination as a pulsatile abdominal mass or abdominal bruit.

Ruptured AAA is a different story. Anterior ruptures into the abdominal cavity have the highest mortality and rarely reach the hospital alive. Posterior ruptures into the retroperitoneum limits bleeding somewhat, having a lower mortality. The classical triad involves severe acute abdominal pain, a pulsatile abdominal mass, and haemodynamic instability. A symptomatic AAA is an indication of threatening rupture, including abdominal pain and tender AAA on palaption. Less than 1/3 of patients with rupture have a known history of AAA.

Cullen’s sign (periumbilical ecchymosis) and Grey-Turner sign (flank ecchymosis) are signs of ruptured AAA.

Diagnosis and evaluation

Palpation for a pulsatile abdominal mass is sensitive for normal-weighted people with larger aneurysms, but the larger the person’s abdominal circumference and the smaller the aneurysm, the lower the sensitivity.

Diagnosis is based on imaging which shows an aneurysmal dilation > 50% of the normal diameter, or > 3 cm. Imaging may be achieved with ultrasound or CT.

Treatment

Conservative treatment involves regular surveillance with ultrasound (1 – 3x a year), normalisation of blood pressure, smoking cessation, blood lipid reduction, and removal of other risk factors. This is indicated for asymptomatic AAAs which are < 5,5 cm.

Elective surgery is indicated for aneurysms which are > 5,5 cm, or which expand > 1 cm per year. Emergency surgery is indicated for ruptured AAA. Symptomatic (threatening) AAA must also be treated immediately.

Surgery may be endovascular or open. Endovascular aneurysm repair (EVAR) is preferred. Entry to the aorta is achieved through the femoral or iliac arteries. An expandable stent graft is place inside the lumen of the AAA.

Screening

Many countries have screening programmes for AAAs, screening people above a certain age (usually 50-65) with ultrasound.