ELN and triple-A syndrome: The hallmark histopathological features of AAA are: (1) degradation of the ECM, especially of the elastin fibers; (2) apoptosis and subsequent loss of vascular smooth muscle cells (VSMCs), which are responsible for providing vascular tone and contractility; and (3) accumulation and activation of inflammatory cells such as macrophages, which in aggregate, lead to degeneration of the vascular wall and aneurysm formation (18, 19).