Abdominal aortic aneurysm (summary)

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This is a basic article for medical students and other non-radiologists

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

Reference article

This is a summary article; read more in our article on abdominal aortic aneurysm.

Summary

  • epidemiology
    • prevalence of rupture increases with age
    • males more commonly affected than females
    • prevalence is almost 10% in people over 65 years old
    • 10 commonest cause of death in Western populations
  • presentation
    • may be asymptomatic; aneurysms most commonly discovered incidentally at abdominal imaging
    • pain if there is a rapid change in diameter or impending rupture
    • pain and shock in rupture
  • pathophysiology
    • many processes may cause aneurysms
      • atherosclerosis is by far the commonest cause
      • inflammatory, infective and vasculitic conditions may also be causes
  • investigation
    • US for population screening and monitoring small aneurysms
    • CT is the gold-standard for aneurysm assessment
    • CT is used in the acute setting of potential aneurysm complication
  • treatment
    • small aneurysms without signs of complication are followed up
    • the larger the aneurysm the more likely it is to rupture
      • aneurysmal rupture carries a significant risk of death
    • larger, complicated aneurysms need treatment
      • endovascular (EVAR) or open surgery can be performed
    • symptomatic aortic aneurysms are treated urgently regardless of diameter

Role of imaging

  • detection of abdominal aortic aneurysm
  • monitoring of the rate of growth
  • pre-operative planning
  • post-operative follow-up

Radiographic features

Plain radiograph

An aneurysm may be visible as an area of curvilinear calcification in the paravertebral region on either abdominal or lumbar spine radiographs performed for alternative indications.

Ultrasound

Ultrasound assessment is simple, safe and inexpensive. It has a reported sensitivity of 95% and specificity close to 100% . It is usually the preferred choice for monitoring small aneurysms.

CT 

CT angiography is considered the imaging gold standard but has a high radiation dose. Excellent for pre-operative planning as it accurately delineates the size and shape of the abdominal aortic aneurysm and its relationship to branch arteries and the aortic bifurcation.

As aneurysms increase in size the risk of complications increase. CT can be used to make an assessment of rupture, impending rupture or contained leak.

Recommendations may vary, but in general, abdominal aortic aneurysms with the following growth rates and diameters have high risk of rupture and may warrant urgent repair :

  • growth rate exceeds 1 cm per year or 5 mm in 6 months
  • diameter of at least 5.5 cm in men or 5 cm in women