What could cause an aortic aneurysm to burst?

Ruptured aneurysm. An abdominal aneurysm can rupture for many reasons. Most common is size. As the aneurysm enlarges the wall gets weaker. We know that aneurysms over 5 cm have a higher rupture rate and those should be operated on electively. Other factors making rupture more likely would be uncontrolled high blood pressure and infection in the wall of aneiurysm.