What are the causes of an aortic aneurysm?

Causes of Aortic Aneurysm

Aortic aneurysms result from multiple distinct etiologies, with hypertension being the dominant risk factor (present in 80-85% of cases), followed by genetic/hereditary conditions (20% of thoracic cases), atherosclerotic degeneration, connective tissue disorders, and less commonly trauma, infection, or inflammatory vasculitis. 1

Primary Etiologic Categories

Degenerative/Atherosclerotic Disease

• Hypertension is the single most important modifiable risk factor, present in 85% of patients with ruptured aneurysms and 52% of those with non-ruptured aneurysms 1
• Atherosclerotic changes with medial degeneration affect over 90% of aortic aneurysm surfaces, particularly in the infrarenal abdominal aorta 1
• The underlying mechanism involves medial degeneration with fragmentation of elastic fibers, reduced smooth muscle cell viability, and extracellular matrix degradation 1, 2
• Smoking is a critical environmental risk factor that accelerates aneurysm formation and growth 3, 4
• Hypercholesterolemia contributes to atherosclerotic vessel changes, though 60% of patients have cholesterol levels below 240 mg/dL 1
• Male sex confers significantly higher risk, with male-to-female ratios of 2-4:1 for most aneurysm types 1
• Advanced age (>65 years) is strongly associated with degenerative aneurysm formation 4

Genetic and Hereditary Conditions

• Genetic factors are involved in approximately 20% of thoracic aortic aneurysm cases 1
• Marfan syndrome (MFS) causes autosomal dominant aortopathy with early-onset aortic root aneurysms, typically presenting at 30-50 years of age 1
• Loeys-Dietz syndrome (LDS) follows autosomal dominant inheritance and causes aggressive thoracic aortic disease 1
• Bicuspid aortic valve (BAV) is associated with aortic root aneurysms in 20-30% of affected patients, though genetic testing is usually negative due to complex polygenic inheritance 1
• Familial thoracic aortic aneurysm disease identifies disease-causing mutations in approximately 20% of cases through genetic testing 1
• Turner syndrome and vascular Ehlers-Danlos syndrome are additional genetic conditions predisposing to thoracic aortic aneurysms 1

Location-Specific Etiologies

Aortic Root Aneurysms:

• Can be idiopathic, associated with heritable thoracic aortic disease (syndromic or non-syndromic), or found in 20-30% of bicuspid aortic valve patients 1
• Patients are typically younger (30-50 years) with equal sex distribution 1

Supra-coronary Ascending Aortic Aneurysms:

• Caused by atherosclerosis related to hypertension in older patients (59-69 years) with 3:1 male predominance 1
• Can result from medial degeneration isolated or associated with aortic valve disease including BAV 1
• Primary bacterial infection or syphilis are uncommon causes 1

Aortic Arch Aneurysms:

• Typically linked to atherosclerosis when occurring with adjacent ascending or descending aorta involvement 1
• Cystic medial degeneration primarily affects arch aneurysms extending from ascending aorta disease 1

Traumatic Causes

• Blunt chest trauma accounts for 15-20% of deaths in high-speed accidents, with 95% of injuries occurring at the aortic isthmus 1
• Deceleration injuries can extend into the aortic arch 1
• Iatrogenic trauma from cardiac catheterization (diagnostic or interventional procedures) can cause aortic injury 1
• Aortic dissection may occur after prior aortic valve replacement, with the mechanism potentially related to jet lesions producing post-stenotic dilatation 1
• Resuscitation procedures can lead to aneurysm formation and aortic rupture 1

Inflammatory/Infectious Causes

• Vasculitis can destroy medial layers of the aortic wall, leading to weakening and aneurysm formation 1, 5
• Takayasu's arteritis and giant cell arteritis are rare but recognized causes of aneurysm formation 1
• Suppurative bacterial or fungal aortitis causes focal destruction of vessel walls but is uncommon 1
• Behçet's disease, aortitis associated with rheumatoid disease, and inflammatory abdominal aortic aneurysm represent additional inflammatory etiologies 1

Key Clinical Pitfalls

Do not assume all aneurysms are atherosclerotic in origin. Young patients (<50 years) with thoracic aortic aneurysms require evaluation for genetic conditions, particularly if there is family history or syndromic features 1. The microscopic changes in genetic aortopathies resemble degenerative changes but occur at significantly earlier ages 1.

Recognize that chronic obstructive pulmonary disease (COPD) is an independent risk factor beyond its association with smoking, contributing to increased rupture risk 1.