Abdominal Aortic Aneurysm (AAA)

• • 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

Epidemiology

• • 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:

  • -Marfan syndrome

    -Ehlers-Danlos syndrome

    -Behçet disease

    -Syphilis

    -Long-term sequelae of aortic dissection

  • Risks:

  • -Smoking

    -Hypertension (HTN)

    -COPD

  • 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

Symptoms and Signs

• • 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

Laboratory Findings

• • CBC abnormal

Imaging Findings

• • Abdominal x-ray: 20% calcifications in outer aortic wall on lateral view

  • US

  • -Inexpensive screening test, measures size and position

    -Used in cases of groin pseudoaneurysm to evaluate proximal anastomosis in abdomen

  • CT scan

  • -Diagnostic, accurate sizing, and provides information about anatomy: renal anomalies, retroaortic renal veins, ...