What are the likely causes of an abdominal aneurysm in a non-smoking male?

Causes of Abdominal Aortic Aneurysm in Non-Smoking Males

In non-smoking males, abdominal aortic aneurysms primarily result from hereditary/genetic predisposition, advancing age (especially >65 years), hypertension, and underlying aortic medial degeneration with altered metalloproteinase activity. 1

Primary Etiologic Mechanisms

Genetic and Familial Factors

• First-degree male relatives of AAA patients have 2-4 times the normal risk, with relative risk as high as 18 for male siblings of male probands, suggesting a single dominant gene effect 1
• Among offspring of patients with ruptured AAA, 21% of sons older than 45 years had aortic enlargement to at least 3.0 cm diameter 1
• Familial AAA accounts for 15-28% of cases in surgical series, making this the strongest non-smoking risk factor in males 1

Age-Related Degeneration

• AAA prevalence increases dramatically after age 50, reaching 12.5% in men aged 75-84 years even in general populations 1
• For non-smokers specifically, prevalence ranges from 1.3% at ages 45-54 to approximately 5-7% by age 75-84 1
• The infrarenal abdominal aorta is most susceptible, accounting for 60% of all aortic aneurysms 2

Biological Mechanisms

• Most aneurysms form due to aortic medial degeneration involving altered tissue metalloproteinases that diminish arterial wall integrity, not simply atherosclerotic disease 1
• This process involves thinning of the media and adventitia due to loss of vascular smooth muscle cells and extracellular matrix degradation 3
• Inflammatory cell infiltrate, neovascularization, and production of various proteases and cytokines contribute to AAA development 4

Contributing Risk Factors in Non-Smokers

Cardiovascular Comorbidities

• Hypertension is present in 52-85% of AAA patients and dramatically increases wall stress 1, 2
• Coronary artery disease, previous myocardial infarction, and peripheral arterial disease are significantly more prevalent in AAA patients than age-matched controls 1, 5
• Elevated lipoprotein(a) levels occur in AAA patients independent of other cardiovascular risk factors 1

Atherosclerotic Markers

• Thoracic aortic atheromata detected by transesophageal echocardiography independently predict AAA (odds ratio 11.4) 1
• Increased common carotid arterial intima-media thickness correlates with AAA presence 1

Clinical Context for Non-Smoking Males

Screening Implications

• Among men aged 65-75 who have never smoked, an estimated 1,783 would need to be screened to prevent 1 AAA-related death in 5 years, compared to 500 ever-smokers 1
• The U.S. Preventive Services Task Force gives a "C" recommendation (selective screening) for non-smoking males aged 65-75, particularly those with strong first-degree family history requiring surgery 1
• One-time ultrasound screening may be considered for non-smoking males with multiple risk factors: family history, hypertension, coronary artery disease, or age >65 years 1, 5

Important Caveats

• While smoking is the strongest modifiable risk factor, genetic predisposition and age remain powerful independent drivers of AAA formation in non-smokers 1, 3
• The presence of three-vessel coronary artery disease increases AAA risk even without smoking history 1
• Male sex itself confers substantially higher risk than female sex at all ages, independent of smoking status 1, 3