Ep 173 – Abdominal aortic aneurysm

Abdominal aortic aneurysms (AAAs) are potentially life-threatening and have a poor prognosis if ruptured. Arterial aneurysms are defined as a permanent localised dilatation of the vessel, enlarging significantly compared to a relatively normal diameter of the adjacent artery. An AAA is characterised by abnormal focal dilation of the abdominal aorta that is often detected incidentally or only at the time of rupture. In this episode, Dr Roger Henderson looks at AAA risk factors, clinical presentations, diagnostic investigations, screening, treatments and prognosis.

Key take-home points

• Abdominal aortic aneurysms (AAAs) represent a critical and potentially life-threatening vascular condition, characterised by abnormal dilation of the abdominal segment of the aorta.
• AAA is usually defined as having an aortic diameter of 3 cm or greater, with most AAAs arising from below the level of the renal arteries.
• Degradation of the extracellular matrix, particularly the loss of structural proteins such as elastin and collagen, leads to the progressive aortic dilation seen in an AAA.
• Smoking is the most significant modifiable risk factor for AAA. Each year of smoking increases the relative risk of an AAA by 4%.
• Other contributing factors include hypertension, hyperlipidaemia and a family history of aneurysm.
• Based on autopsy studies, AAA frequency varies from 0.5% to 3%.
• AAAs are often asymptomatic and frequently discovered incidentally during imaging studies conducted for unrelated reasons.
• When symptoms do occur, they typically include a pulsatile abdominal mass, abdominal pain and, in the case of impending rupture, severe pain accompanied by hypotension and signs of shock.
• Ultrasound is the preferred initial screening tool due to its non-invasive nature, widespread availability and high sensitivity and specificity.
• Never delay diagnosis and management of a ruptured AAA while waiting for the results of any imaging.
• Computer tomography angiography is the recommended definitive imaging modality for AAA rupture, as it provides detailed anatomical information and is helpful with preoperative planning.
• For larger aneurysms or those demonstrating rapid growth, elective surgical repair is indicated.
• Urgent surgical repair is indicated for any patient with ruptured or symptomatic AAA.
• The two primary surgical options are open surgical repair (OSR) and endovascular aneurysm repair (EVAR). OSR involves direct surgical exposure of the aorta and placement of a synthetic graft, whereas EVAR is a minimally invasive procedure that involves the insertion of a stent-graft via the femoral arteries to exclude the aneurysm sac from circulation.
• Ruptured AAAs are a surgical emergency with a high mortality rate, even with prompt intervention. Over half of patients die before they even get to the hospital.
• In contrast to patients with a ruptured aneurysm, the prognosis following elective repair of AAA is good to excellent, with an estimated 70% of patients surviving for 5 years after repair.

Key references

1. NICE. 2020. https://www.nice.org.uk/guidance/ng156.
2. GOV.UK. 2023. https://www.gov.uk/government/collections/population-screening-programmes-nhs-abdominal-aortic-aneurysm-aaa-programme.
3. Sakalihasan N, et al. Nat Rev Dis Primers. 2018;4(1):34. doi: 10.1038/s41572-018-0030-7.
4. Golledge J, et al. Eur Heart J. 2023;44(29):2682-2697. doi: 10.1093/eurheartj/ehad386.
5. InformedHealth.org [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK441574/.
6. Wanhainen A, et al. Eur J Vasc Endovasc Surg. 2024;67(2):192-331. doi: 10.1016/j.ejvs.2023.11.002.