Abdominal Aortic Aneurysm

What is 'Abdominal Aortic Aneurysm'?

An abdominal arterial aneurysm (AAA) is the dilation of a blood vessel at the level of the renal arteries. Usually, aneurysms can occur in arteries at any location; however, the most common area would be the abdominal aorta and the arteries at the base of the brain. People with aorta diameter greater than 3.0cm would consider having an aortic aneurysm, in which an average size would be around 2.0cm.[1]

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Risk factors of developing an Abdominal Aortic Aneurysm

  • Age, Gender and ethnicity

    • The risk of getting AAA increases significantly for people with age 60 and above.

    • The development of AAA is more common in males (1.3-8.9%) than females (1.0-2.2%).[2]

    • Black or Asian race are less likely to develop AAA.

  • Smoking

    • Weakening of the aortic walls by increases blood pressure, causing the vessel wall to become less elastic. Thus increases the chance of developing AAA and rupture of arteries.

  • Family history - genetics

  • Atherosclerosis

    • Hardening of the arteries due to the deposition of fat and other substances in the lining of a blood vessel.

  • Coronary artery disease and Peripheral vessels disease

  • Hypertension

    • Can damage and weaken the wall of aorta

  • Negative association with diabetes

  • Other aneurysms - having an aneurysm at other areas before.

Causes of Abdominal Aortic Aneurysm

The development of AAA is due to a degenerative process of layers of the vessel wall. This tends to occur when there is a failure of the structure proteins: collagen muscles and elastin of the aorta, hence gradually weakens its wall. However, the causes of failure are unknown.

 

The degenerative process can be characterised into four events:

  • Infiltration of the vessel wall by lymphocytes and macrophages

  • Destruction of elastin and collagen in the tunica media and external layers by enzymes secreted by macrophages.

  • Loss of smooth muscle cells with thinning of the tunica media.

  • Neovascularisation - a development of new blood vessels due to trauma or disease.

The number of lamellar units, which is the main component of the aortic walls, is lower in the infrarenal aorta than the thoracic aorta. This is why the formation of an aneurysm at the infrarenal aorta is higher than the thoracic area.

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Diagnosis

Diagnosis is a crucial step for an early discovery of AAA in which any aneurysms detected can be repaired before they rupture. If smaller bulges are found, they can be checked regularly to measure their growth rates. The accuracy of the clinical examination is significantly reduced by obese body habitus and small aneurysm size.

Ways to diagnose the presence of AAA:

1. Ultrasound (US)

  • Ultrasound is simple, safe and inexpensive with sensitivity of 95%[3]. It is the preferred modality of choice for monitoring of small aneurysms, especially in thin subjects.

2. Computed Tomography Angiography (CTA) Scan

  • CTA determines the exact location, aortic size, shape, the involvement of visceral arteries and the presence of intraluminal thrombus. It even evaluates the abdomen in more detail in patients with a specific abdominal complaint. As a result, better imaging of suprarenal aneurysms is produced.

  • CTA is superior to US in detecting and sizing. However, CTA has high radiation doses.

3. Magnetic Resonance Angiogram (MRA)

  • ​Provides the same information as CTA but is more expensive and less widely available. However, this method is a more appropriate option for young patients with allergies radiographic contrast media and renal failure.

However, screening also could also bring more disadvantages:

  1. Over-diagnosis - some aneurysms are repaired even though they unlikely to rupture.

  2. Surgical procedure itself may cause serious complications.

  3. Unnecessary psychological distress to patients and increases the level of anxiety.

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Symptoms

Small aneurysms are generally asymptomatic in most patients. Only people with enlarging abdominal aneurysms would experience the following:

  • Abdominal pain or pain on the side of your abdomen

  • Back ache

  • A pulse around the belly button area

If the abdominal aorta ruptures, it would cause sudden back pain as well as dizziness, loss of consciousness due to a large amount of blood being lost. Eventually, circulatory would collapse.

Treatments

The treatment of unruptured AAA is recommended when it reaches 5cm to 5.5cm.[4]

  • Risk factor modification

    • Smoking cessation - to reduce the rate of aneurysmal growth

    • Antihypertensive agents and statins - to minimise hypertension

    • Exercise - does not influence the risk for rupture and reduces the rate of growth.

  • Beta-blockers

  • Antibiotic therapy

  • Open surgery

    • The aneurysm is opened, and replaced by an artificial vessel (graft)

  • Endovascular Aneurysm Repair (EVAR)

    •  is the minimally invasive procedure of inserting a stent inside the abdominal aorta, usually deployed inside the aneurysm through femoral access. The aneurysm is, however, not physically removed.

    • EVAR poses several benefits to the open surgery method, including

      • Faster recovery

      • Less pain

      • Less complications

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[1] Paravastu SC, Jayarajasingam R, Cottam R, Palfreyman SJ, Michaels JA, (2017)

Online version available at:  https://www.ncbi.nlm.nih.gov/books/NBK441574/

[2]  Bhardwaj Gaurav: Aortic aneurysm

Online version available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290913/#j_jtim-2016-0008_ref_001

[3] Bhardwaj Gaurav: Aortic aneurysm

Online version available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290913/#j_jtim-2016-0008_ref_001

[4]Palma M. Shaw; John Loree; Ryan C. Gibbons. (2019)

Online version available at: https://www.ncbi.nlm.nih.gov/books/NBK470237/

[5] Wongkarnpat: Abdominal Aortic Aneurysm. 2015

Online version available at: http://www.wongkarnpat.com/viewpat.php?id=1754#.XeZbNZMzbOQ

[6] Eric M. Isselbacher: Thoracic and Abdominal Aortic Aneurysm. 2005

Online version available at: https://ahajournals.org/doi/10.1161/01.cir.0000154569.08857.7a

[7] Arabella Hau: Aneurysm. 

Online version available at: https://www.sutori.com/story/aneurysm--9N3q9oMugykKmyPsbZMtj9zd

Written by Praewa (Mind) Wongsriyanon 

Year 13 Student at Shrewsbury International School Bangkok