Atherosclerosis may weaken the wall of the aorta such that it bulges out to form an aneurysm. An atherosclerotic aortic aneurysm typically occurs in the abdominal portion below the renal arteries, as shown here, but aneurysms can form in the more proximal aorta as well as in branches of the aorta. Aortic aneurysms that get bigger than 5 to 7 cm are more prone to rupture.