Aneurysm of the Abdominal Aorta
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- An infrarenal aorta ≥3 cm in diameter is considered aneurysmal.
- Fusiform aneurysm: Involves the whole circumference or wall of the artery
- Saccular aneurysm: Does not involve the full circumference, often appears as an asymmetrical bleb or blister on side of aorta. Clinical presentation relates to aneurysm location, size, type, and comorbid factors affecting patient. The majority are asymptomatic. May present with rupture, embolism, or thrombosis. Treatment and indications for surgical repair dictated by risk of rupture, risk of surgical repair, and estimated patient life expectancy.
- System(s) affected: Cardiovascular; Neurologic; Heme/Lymphatic/Immunologic
- Synonym(s): Aortic aneurysms; AAA
Incidence of AAA, risk of rupture, and operative morbidity and mortality all rise with age.
Rare in children; may be associated with umbilical artery catheters, connective tissue diseases, arteritides, or congenital abnormalities.
- Frequency increases >50 years of age
- Predominant sex: Male > Female (5:1) (1)
- >15,000 deaths per year in US
- 10th leading cause of death in men 65–75
- 8% of men age >65
- Depends on risk factors associated with AAA
- Prevalence of AAAs 2.9–4.9 cm in diameter ranges from 1.3% for men aged 45–54 to 12.5% for men 75–84. Data for women are 0% and 5.2%, respectively (2); however, when detected, women presented at an older age and were more likely to present with a ruptured AAA. Female sex is an independent risk factor for death from AAA (3).
Older age, male, Northern European ethnicity, family history, smoking, hypertension (HTN), hyperlipidemia, peripheral vascular disease, peripheral aneurysms, chronic obstructive peripheral disease (COPD), obesity (3)Genetics
- Familial aggregations exist: Aneurysms may develop at an earlier age.
- 2× risk of AAA if 1st-degree relative with AAA (1)
- Marfan syndrome
- Ehlers-Danlos syndrome
- Polycystic kidney disease
- Tuberous sclerosis
- Address cardiovascular disease risk factors.
- Follow screening guidelines: US screening for detection of AAA in male patients, 65–75, who have ever smoked and men >60 who are siblings or offspring of patients with AAA (USPSTF Guideline).
- Vascular inflammatory degenerative disease, with major role of matrix metalloproteinases and inflammatory markers that result in aortic medial degeneration (2)
- Gradual and/or sporadic expansion of aneurysm and accumulation of mural thrombus
- Mural thrombus can contribute to an area of localized hypoxia, thus further weakening the aneurysm.
- Aneurysms tend to expand over time. (Laplace law: T (wall tension) = pressure × radius. Wall tension directly related to BP and radius of artery.) When wall tension exceeds wall tensile strength, rupture occurs (3).
- Average small AAA (<5.5 cm) grows at rate of 2.6–3.2 mm/yr. Larger aneurysms grow faster rate, as do aneurysms in current smokers; otherwise no identifiable risk factors to assess which small AAAs will advance to require further intervention.
- Annual growth rate of 2.2 mm/yr average for small aneurysms but increased in smokers; decreased in diabetics (4).
- 60–80% of AAAs between 40 and 49 mm will enlarge and require surgery in 5 years.
Degenerative: Atherosclerotic (80%); other causes: Inflammatory diseases (5%), trauma, connective tissue disorders, infection (Brucella, Salmonella, staph, tuberculosis)
Commonly Associated Conditions
- HTN, myocardial infarction (MI), heart failure, carotid artery, and/or lower extremity peripheral arterial disease
- Screening for thoracic aneurysm should also be considered.