Aneurysm refers to pathologic dilation of an artery to greater than 1.5 times its normal size. True vascular aneurysms are due to degenerative processes in the wall of the artery. Aneurysms can be solitary or multiple and are sometimes found in association with various clinical syndromes, including forms of vasculitis or connective tissue diseases. Aneurysms are typically classified by major shapes, either fusiform (tubular) or saccular (eccentric). Ectasia is another broad term for an enlarged vessel, but is not necessarily pathological. Rupture is a dreaded complication of aneurysms that can lead to extensive, difficult to control bleeding. Aneurysms can also clot, or thrombose, and rapidly occlude the involved vessel, leading to acute distal ischemia.