Abdominal aortic aneurysm

Abdominal aortic aneurysms (AAA) are focal dilatations of the abdominal aorta measuring 50% greater than the proximal normal segment, or >3 cm in maximum diameter.

  • represent the tenth most common cause of death in the Western world
  • prevalence increases with age
    • ~10% patients older than 65 have an AAA
  • males are much more commonly affected than females (4:1 male/female ratio)

Since most AAAs are asymptomatic unless they leak or rupture, they are commonly diagnosed incidentally during imaging for other indications.

Uncommonly, unruptured aneurysms may present with abdominal or back pain. Large aneurysms may present as a pulsatile abdominal mass.

The most significant complication is abdominal aortic rupture, which presents with severe abdominal or back pain, hypotension, and shock.

  • mortality rate from a ruptured AAA is high
    • 59-83% of patients die prior to hospitalization or surgery
    • for those who undergo operative repair, mortality rate is ~40%
    • for comparison, mortality from elective surgical repair is 4-6%
  • ruptured abdominal aortic aneurysms are discussed in more detail separately

Other complications include:

  • detection of AAA
  • monitoring of growth rate
  • preoperative planning
  • postoperative follow-up

An aneurysm may be visible as an area of curvilinear calcification in the paravertebral region on either abdominal or lumbar spine radiographs. Although not adequate for AAA detection or follow-up, x-ray may be sufficient for initial detection and diagnosis.

Ultrasound is optimal for general AAA screening and surveillance, because it is fast, spares the use of ionizing radiation and intravenous contrast, and is relatively inexpensive. The sensitivity and specificity approach 100% 19; however, it should be noted that visualization is poor in 1% to 3% of patients due to patient habitus or overlying bowel gas 19.

Although excellent for following lesions, ultrasound does not provide sufficient detail for procedural planning or more complex lesions. Given a reported range in measurement error of 4 mm 12, ultrasound cannot be reliably used in evaluation for endovascular treatments and assessment of regional branch vessels.

CT angiography (CTA) is considered the gold standard for evaluation, but exposes the patients to high radiation doses. It is excellent for pre-operative planning as it accurately delineates the size and shape of the AAA and its relationship to branch arteries and the aortic bifurcation. Oblique reformations enable accurate measurements in non-orthogonal planes. CTA is superior to ultrasound in detecting and measuring common iliac artery aneurysms.

Signs of frank rupture include:

Signs of impending rupture or contained leakage:

An increasing diameter of the aneurysmal sac of 5 mm over a 6-month interval or a diameter of 7 cm are also considered to be at high risk for rupture and warrant urgent repair.

Offers lack of ionising radiation, but is more costly, less widely available, and the examination is substantially lengthier.

Catheter-based angiography alone is inadequate for pre-procedural evaluation of AAA. While digital subtraction angiography (DSA) is superb for delineating regional branch vessels, it can be misleading and mask true aneurysm size in the setting of mural thrombus.

Certain features and relevant negatives regarding AAA should be included in the radiology report - especially if this is a new or undocumented finding:

Also see: reporting tips for aortic aneurysms

The natural history of abdominal aortic aneurysms is variable; some small aneurysms do not appear to change, while others slowly expand and become at risk for eventual rupture 19,21. A number of clinical factors (e.g. smoking, gender, blood pressure) are known to contribute. Ultimately, the primary clinical question is whether and when to intervene in order to avoid aortic rupture.

In terms of imaging, there remains debate about the best criteria for predicting AAA rupture and therefore indications for operative intervention. Prognostic imaging criteria include:

  • maximum transverse diameter
    • most widely used and validated method 19,20
    • 2018 Society of Vascular Surgery recommendations generally recommend intervention for AAA ≥5.4 cm, and surveillance for smaller diameter lesions 19
    • young, healthy (especially female) patients may benefit from intervention for lesions between 5.0 - 5.4 cm 19
    • most study data is based on fusiform aneurysms; it is debated whether the more uncommon saccular aneurysm is at higher risk for rupture at smaller transverse diameter 19
  • rate of aneurysm growth
    • enlargement in transverse diameter ≥5 mm in 6 months may be an indication for intervention 17
  • symptomatic lesions 19

In patients with a connective tissue disorder (e.g. Marfan syndrome), especially those with a bicuspid aortic valve, surgical treatment may be considered even with a diameter smaller than 5.0 cm.

Follow-up intervals for imaging an enlarged infrarenal abdominal aorta from initial detection 11:

  • <2.5 cm: follow up not needed
  • 2.5-2.9 cm: 5 year interval
  • 3.0-3.4 cm: 3 year interval
  • 3.5-3.9 cm: 2 year interval
  • 4.0-4.4 cm: 1-year interval
  • 4.5-4.9 cm: 6-month interval
  • 5.0-5.5 cm: 3-6 month interval
  • >5.5 cm: treatment

Management options include:

  • surveillance (see above)
  • endovascular aneurysm repair (EVAR)
    • if the anatomy permits, EVAR is preferred vs surgical repair
    • aneurysm-related mortality has been shown to be much lower with EVAR vs surgical repair
  • resection (open surgical repair)
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Article information

rID: 826
System: Vascular
Synonyms or Alternate Spellings:
  • AAA
  • Abdominal aortic aneurysm (AAA)
  • Abdominal aortic aneurysms
  • Abdominal aortic aneurysmal dilatation
  • AAA's

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