Abdominal Aortic Aneurysm (AAA)

Overview
  • Abdominal Aortic Aneurysms (AAA) are True Aneurysms of the abdominal aorta which generally occur below the level of the renal arteries and above the aortal bifurcation.
Pathogenesis
  • The most common etiology of AAA is atherosclerosis and in such cases the AAA can be thought of as a subtype of atherosclerotic aneurysms. However, hereditary factors clearly contribute to the generation of AAAs as there is some familial clustering of this condition. Regardless, inflammation associated with atherosclerosis leads to destruction, thinning and thus weakening of the vascular wall, specifically the tunica media, which contributes to aneurysmal dilation of the vessel.
Morphology
  • AAAs are usually greater than 4cm in diameter and can manifest in both fusiform or saccular forms. The dysfunctional endothelium within the aneurysm combined with abnormalities in blood flow often leads to the generation of mural thrombi within the aneurysm. Additionally, bacterial infection of the atherosclerotic vascular wall can lead to a mycotic aneurysm which further accelerates weakening and expansion of the aneurysm due to increased inflammation associated with microbial infection.
Clinical Consequences
  • Overview
    • AAAs generally produce no symptoms and can be found on physical exam as pulsatile abdominal masses. When large, they can impinge on adjacent structures producing some abdominal pain. However, in most cases they are essentially medical time-bombs which can generate sudden medical emergencies with few, if any warnings.
  • Rupture
    • AAAs can suddenly rupture, leading to catastrophic hemorrhage into the peritoneum, resulting in hemoperitoneum, or hemorrhage into the retroperitoneum. This frequently fatal complication of AAAs increases in probability with increasing aneurysmal diameter.
  • Embolization