• Permanent aortic dilation (at least 50%)
• Classified by etiology (degenerative, inflammatory, mechanical, congenital, dissecting) and by shape (saccular, fusiform)
• Up to 25% of patients have symptoms of aortoiliac occlusive disease as well
• Most are infrarenal; decreased vasa vasorum and elastic lamellae may predispose to aneurysm formation
• Rupture risk correlates with size, following law of LaPlace
• Average expansion rate of 0.4 cm/y depends on aneurysm size, diastolic blood pressure, and chronic obstructive pulmonary disease (COPD)
• For AAA measuring 5.0–5.5 cm, rupture risk is 40% at 5 years
• Suprarenal: Uncommon; extends proximal to renal arteries; low risk for rupture until exceeds 6–7 cm
• Ruptured: Most often ruptures posterolaterally to left; if exsanguination delayed, likely contained rupture that eventually becomes free rupture
• Inflammatory: Characterized by inflammatory response external to aneurysmal wall, with inflammation usually confined to anterior aorta; 25% have ureteral obstruction, which results in dense, shiny fibrotic reaction enveloping adjacent viscera
• Infected (mycotic): Bacterial contamination of preexisting aneurysm (different from Salmonella causing false aneurysm); gram-negative infections result in higher rupture rates
• Ruptured AAA is the 13th leading cause of death in the United States (15,000 deaths yearly)
• Present in 2% of population and incidence is increasing
• More men affected than women (4:1)
• 5% of patients with coronary artery disease have AAA
• 50% of patients with femoral or popliteal aneurysms have AAA
• 19% incidence among first-degree relatives
• Rare causes:
• Diabetes appears to exert protective effect
• Increased incidence of rupture during fall and winter months
• Strep, Haemophilus, Staph, E coli, other gram-negative pathogens, and fungi identified in infected AAA
• Rarely produces symptoms if intact
• Painless, pulsatile abdominal mass above umbilicus; may be uncomfortable on palpation
• Palpation may be difficult in obese patients
• Rarely produces back pain from pressure on nerves
• Severe paincaused by inflammatory or ruptured AAA or acute expansion
• Congestive heart failure from aortocaval fistula, GI bleed from duodenal erosion, and pyelonephritis from ureteral obstruction are rare
• Rupture causes sudden, severe abdominal/back pain radiating to back or inguinal area, faintness or syncope, shock; often tender pulsatile mass present
• Triad for rupture: Pain, pulsatile abdominal mass, hypotension found in < 67% of patients
• Inflammatory: Abdominal pain, tender AAA
• Infected: Rapidly enlarging tender pulsatile mass, fever
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