10th March 2024

Abdominal Aortic Aneurysm

Background

An abdominal aortic aneurysm (AAA) is a segmental, full-thickness dilation of the abdominal aorta 50 per cent greater than the normal aortic diameter and is the most common true arterial aneurysm. In adults, a diameter greater than 3 cm is considered an aneurysm. An abdominal aortic aneurysm requires timely management; if not, it can progress to further expansion, rupture, haemorrhage, and death. AAA has a 50 – 80% mortality, and the most common risk factors are the following:

• Older age
• Male sex
• Cigarette smoking
• Positive family history of AAA
• Other large artery aneurysms (e.g., iliac, femoral, popliteal)
• Atherosclerosis
• Hypertension

Additionally, most family-based studies found a predisposition for a patient to have an abdominal aortic aneurysm if a relative had one but not if they had a thoracic aortic aneurysm. 

Classification 

Although an infrarenal aorta with a maximum diameter ≥3.0 cm is considered aneurysmal, the following classification based on diameter does not predict clinical events. 

• Small aneurysms have a diameter of <4.0 cm
• Medium aneurysms have a diameter between 4.0 and 5.5 cm
• Large aneurysms have a diameter >5.5 cm
• Very large aneurysms have a diameter ≥6.0 cm

Clinical presentation 

AAA can be asymptomatic, and despite advances in screening, it continues to be a significant cause of death in the elderly. When symptomatic, it usually means that there has been a rapid change in the aneurysm’s configuration. Patients will often complain of abdominal, back, or flank pain. Sometimes, patients can present signs of limb ischemia or other systemic manifestations like fever or malaise. The most common signs and symptoms of AAA rupture are severe pain, hypotension and a pulsatile abdominal mass. In some cases, symptoms might be unspecific when a retroperitoneal rupture occurs.

Diagnosis 

AAA diagnosis can be made clinically when the aneurysm is greater than 5.5 cm; however, a CT is considered the test of choice for symptomatic AAA. When asymptomatic, abdominal ultrasonography is recommended for follow-up in patients with small and medium-sized aneurysms when managed conservatively. When considering a surgical approach, contrast-enhanced CT aortography is used. 

Management

Once AAA is confirmed, the management will be based on the diameter and whether the presentation was symptomatic or asymptomatic. If the AAA ruptures, surgical management can be offered, and imaging is ideal but not required, especially when patients are hemodynamically unstable. Additionally, resuscitation fluids should be aimed to maintain mentation and stabilise blood pressure and heart rate. When patients are stable, imaging can be performed urgently to determine if endovascular repair is possible. 

Thoracic Aneurysm 

Like AAA, thoracic aneurysms affect 5 to 10 patients per million population each year. Presentation may be asymptomatic, but where symptoms are present, the patient may report chest pain and tenderness, back pain, cough, hoarseness and shortness of breath. Many thoracic aneurysms are first present in the context of a rupture. This should be suspected if the patient has sharp, sudden pain in the upper back, which spreads downward; chest, jaw, neck or arm pain, dysphagia, shortness of breath, hypotension and altered consciousness state. A CT aortogram remains the best diagnostic tool but should not delay management if the patient is unstable. 

References

• Ayala, IADL and Chen, Y.F. (2012). Acute aortic dissection: an update – The Kaohsiung Journal of Medical Sciences. Available at: https://doi.org/10.1016/j.kjms.2011.11.010
• Black, J. & Manning, W. (2021). Overview of acute aortic dissection and other acute aortic syndromes UpToDate. 
• Cantrill et al (2015). Clinical policy: critical issues in the evaluation and management of adult patients with suspected acute nontraumatic thoracic aortic dissection. Annals of Emergency Medicine. Available at: https://www.acep.org/globalassets/new-pdfs/clinical-policies/tad1-2015.pdf 
• Callaway et al (2021). Diagnosis of Thoracic Aortic Dissection in the Emergency Department. RCEM. Available at: https://rcem.ac.uk/wp-content/uploads/2021/12/Diagnosis_of_Thoracic_Aortic_dissection.pdf
• Czerny, M. and Beyersdorf, F., 2020. Abdominal Aortic Aneurysm: Treatment Choice and Volume Effects. Deutsches Ärzteblatt International. Available at: https://doi.org/10.3238/arztebl.2020.0811 
• Dalman, R. & Mell, M. (2021) Overview of abdominal aortic aneurysm In UpToDate. (Accessed: March 23rd, 2022).
• Melo, R.G., Duarte, G.S., Lopes, A., Alves, M., Caldeira, D., e Fernandes, R.F. and Pedro, L.M., 2021, March. Incidence and prevalence of thoracic aortic aneurysms: A systematic review and meta-analysis of population-based studies. In Seminars in Thoracic and Cardiovascular Surgery. WB Saunders.