- Clinical science
Abdominal aortic aneurysm (AAA) is a focal dilatation of the abdominal aorta to more than 1.5 times its normal diameter. AAAs are classified by location as either suprarenal or infrarenal aneurysms. Men of advanced age are at increased risk for their formation; smoking and hypertension are also major risk factors. AAAs are frequently asymptomatic and therefore detected incidentally. Symptomatic AAAs can manifest with lower back pain, a pulsatile abdominal mass, and a bruit on auscultation. Rupture presents with a sudden onset of severe tearing back or abdominal pain, a painful pulsatile mass, and hypovolemic shock. Abdominal ultrasound is the best initial and confirmatory test to diagnose AAAs and determine their extent. Observation, close follow-up, and reduction of cardiovascular risk factors are indicated for small aneurysms, whereas pronounced (> 5.5 cm) or rapidly expanding aneurysms require surgery. Surgical treatment involves open resection of the aneurysm with graft placement or, increasingly, endovascular stent placement. The prognosis is markedly worse if dissection or rupture of the aneurysm occurs. All men between 65 and 75 years of age with a history of smoking and men > 50 years with a positive family history should be screened once with an ultrasound to exclude an AAA.
- Dilation of all three layers of the aortic wall (intima, media, and adventitia) to > 50% of the normal diameter
- Diameter: > 3 cm at the level of the renal arteries (see also
- Peak incidence: 60–70 years (rare in patients < 50 years, who account for only 1% of AAA patients)
- 10% of male patients > 70 years suffering from hypertension
- Sex: ♂ > ♀: ∼ 2:1
- More common in white populations
Epidemiological data refers to the US, unless otherwise specified.
Below the renal arteries
- Most common location , > 90%
- 20% of aneurysms extend into the pelvic arteries.
- Spindle-shaped or saccular (increased risk of rupture)
- Above the renal arteries
- Inflammation and proteolytic degeneration of connective tissue proteins; (e.g., collagen and elastin and/or smooth muscle cells) in high-risk patients → loss of structural integrity of the aortic wall; → widening of the vessel → mechanical stress (e.g., high blood pressure) acts on weakened wall tissue → dilation and rupture may occur.
- The aneurysmatic dilatation of the vessel wall may cause disruption of the laminar blood flow and turbulence. This may cause a bruit on auscultation.
- Possible formation of thrombi in the aneurysm → peripheral thromboembolism
Aortic aneurysms are mostly asymptomatic or have nonspecific symptoms. Therefore, they are often incidental findings on ultrasound or CT scan. Rupture or dissection of the aneurysm is a life-threatening condition (see “Complications” below).
- Lower back pain
- Pulsatile abdominal mass at or above the level of the umbilicus
- Bruit on auscultation
- Peripheral thrombosis and distal atheroembolic phenomena (e.g., blue toe syndrome and livedo reticularis)
- Decreased ankle brachial index
- Ultrasound: best initial and confirmatory test for AAAs 
- CT with contrast: (or MRI): determines AAA rupture, suprarenal involvement, and visceral artery involvement.
- Other imaging: arteriography
Regular monitoring is essential, as the aneurysm size and expansion rate are strong predictors of the risk of rupture!
- (also see table below)
|Abdominal vs. thoracic aortic aneurysm|
|Abdominal aortic aneurysm||Thoracic aortic aneurysm|
| || |
|Epidemiology|| || |
|Clinical features|| || |
|Diagnostics|| || |
The differential diagnoses listed here are not exhaustive.
Reduction of cardiovascular risk factors
- Optimal blood pressure levels (< 120/80 mm Hg)
- Cessation of smoking
- Follow-up for AAA: (aneurysm surveillance): see table below
|Diameter of AAA||Follow-up|
|< 3 cm||No further follow-up|
|3–4 cm||Ultrasound every year|
|4–4.5 cm||Ultrasound every 6 months|
|4.5–5.5 cm||Ultrasound every 3 months|
Indications for repair
Elective repair: for asymptomatic AAAs with any of the following criteria
- Diameter > 5.5 cm
- Aneurysm expanding ≥ 1 cm per year
- Diameter between 4–5.5 cm in young individuals with minimal operative risks and good estimated life expectancy.
- Symptomatic aneurysm (indicative of imminent rupture or a leaking AAA)
- Acutely symptomatic : emergency operation (see “Complications” below)
- Elective repair: for asymptomatic AAAs with any of the following criteria
- Endovascular aneurysm repair (EVAR)
- Open repair: a laparotomy is performed and the dilated segment of the aorta is replaced with a tube graft or Y-prosthesis (bifurcated synthetic stent graft)
- Risk factors: large diameter, rapid expansion, and smoking
- Clinical features
- Impending rupture or contained leak
- Manifested rupture
- Diagnosis: ultrasound, contrast CT → extravasation of contrast agent
- Treatment: open emergency surgery (gold standard) or endoscopic treatment
- Prognosis: high mortality rate (∼ 90% if AAA rupture occurs outside of the hospital)
- Embolism: from thrombotic material of the aneurysm
We list the most important complications. The selection is not exhaustive.
Screening for abdominal aneurysm with abdominal ultrasound
- One-time screening in men aged 65 to 75 years with a history of smoking
- Individuals ≥ 50 years with positive family history