An aneurysm is a blood-filled dilation of a blood vessel caused by a weakening of the vessel’s wall. Aneurysms typically develop because of the general wear and tear of blood pressure on the arteries’ walls, called hemodynamic forces. A weak spot in the artery wall bulges out, giving way to the pressure of the blood flow, forming a sac. For this reason, areas of artery or vessel wall which are submitted to higher blood pressures are more susceptible to aneurysm development, such as the branching points of arteries, called bifurcations. In the same way that a balloon stretches, the aneurysm sac balloons out from the vessel wall usually slowly, progressively becoming weaker.