What are the causes and symptoms of an abdominal aortic aneurysm (AAA)?

Causes and Symptoms of Abdominal Aortic Aneurysm (AAA)

Abdominal aortic aneurysm (AAA) is primarily caused by degenerative atherosclerotic disease, medial degeneration, and altered tissue metalloproteinases that diminish arterial wall integrity, with most patients remaining asymptomatic until rupture occurs. 1

Causes and Risk Factors

Primary Causes:

• Degenerative processes:
  • Atherosclerotic disease 1
  • Medial degeneration with loss of elastin and accumulation of fibrous material 1
  • Altered tissue metalloproteinases that diminish arterial wall integrity 1
  • Inflammatory, proteolytic, and neovascular changes 1

Major Risk Factors:

• Demographic factors:

  • Male gender (4:1 male-to-female ratio) 1, 2
  • Advanced age (prevalence increases after age 50, peaking at 80-85 years) 1, 2
  • Family history (first-degree relatives have 2-4 times higher risk) 1
  • White/Caucasian ethnicity 3

• Lifestyle and medical factors:

  • Smoking (strongest modifiable risk factor, doubles aneurysm expansion rate) 1, 2
  • Hypertension (present in 80% of cases) 1, 2
  • Hypercholesterolemia 1
  • Peripheral arterial disease 1
  • Coronary artery disease 4
  • COPD 1

• Genetic factors:

  • Familial clustering (15-28% of patients have first-degree relatives with AAA) 1
  • Male siblings of male probands have up to 18 times higher risk 1
  • Possible single dominant gene effect 1
  • Genetic syndromes and inflammatory diseases 1

Symptoms

Asymptomatic Presentation:

• Most AAAs are asymptomatic until rupture occurs 1, 2
• Often discovered incidentally during imaging for unrelated conditions 1, 2
• Approximately 30% of asymptomatic AAAs are discovered as a pulsatile abdominal mass on routine physical examination 3

Symptomatic Presentation:

• Common symptoms when present:

  • Back, abdominal, or flank pain (sometimes radiating to the groin) 2
  • Tenderness to palpation overlying the AAA 2
  • Compressive symptoms on adjacent structures 2

• Symptoms suggesting potential rupture:

  • Acute onset of chest, back, and/or abdominal pain 2
  • Recurrent or refractory pain 2
  • Pleural or peritoneal effusions 2
  • Hypotension (in case of rupture) 1

• Other manifestations:

  • Signs of embolism (e.g., blue toe syndrome) 2
  • Obstructive uropathy due to compression 2

Complications

• Rupture:

  • Most serious complication with 75-90% mortality rate 1, 5
  • 54% mortality at 6 hours and 76% at 24 hours after rupture 2
  • Radiological signs include retroperitoneal hematoma, contrast extravasation, high crescent sign, and paraortic fat stranding 1

• Other complications:

  • Thrombosis 3
  • Embolization of atherosclerotic debris 1
  • Aortic valve regurgitation (with proximal extension) 1

Risk Factors for Rupture

• Aneurysm characteristics:

  • Large diameter (risk increases significantly at >5.5 cm for men, >5.0 cm for women) 2
  • Rapid growth (≥5 mm in 6 months or ≥10 mm per year) 1, 2
  • Saccular morphology 1

• Patient factors:

  • Female sex (higher rupture risk at smaller diameters) 1
  • Continued smoking 2
  • Uncontrolled hypertension 1, 2
  • COPD 1

Diagnosis

• Preferred screening modality: Abdominal ultrasonography due to high sensitivity/specificity, safety, and lower cost 4, 3
• Definitive diagnosis: Contrast-enhanced CT for detailed anatomical assessment 2
• Other imaging options: MRI when CT is contraindicated 2

Prevention and Management

• Risk factor modification:

  • Smoking cessation (critical as smoking accelerates AAA expansion) 2
  • Blood pressure control (target SBP 120-129 mmHg if tolerated) 2
  • Lipid management (LDL-C <55 mg/dL) 2
  • Statin therapy (inhibits aneurysm expansion) 2

• Surveillance intervals based on aneurysm size:

  • 3.0-3.4 cm: Every 3 years
  • 3.5-4.4 cm: Every 12 months
  • 4.5-5.4 cm (men): Every 6 months 2

• Intervention thresholds:

  • Men: ≥5.5 cm diameter
  • Women: ≥5.0 cm diameter
  • Rapid growth: ≥5 mm in 6 months or ≥10 mm per year 2

AAA is a potentially life-threatening condition that requires careful monitoring and timely intervention. Understanding the causes and recognizing potential symptoms are crucial for early detection and management to prevent the catastrophic outcome of rupture.