Physical factors in the initiation, growth, and rupture of human intracranial saccular aneurysms

✓ An investigation using glass models disclosed that the apex of a bifurcation is subjected to hemodynamic forces which may initiate the aneurysmal process by producing focal destruction of the internal elastic membrane. A prediction from model studies that turbulence occurs within intracranial aneurysms was confirmed in a clinical study. Bruits, indicative of turbulent blood flow, were recorded from the sacs of 12 of 19 cases studied at the time of craniotomy. Turbulence causes degenerative changes that weaken the wall of an aneurysm and allow it to enlarge. Measurement in four cases revealed that intra-aneurysmal pressure is the same as systemic arterial pressure. An in vitro study of the static elastic properties of human intracranial aneurysms demonstrated that they are relatively nondistensible in comparison to major intracranial arteries. This altered elasticity reflects the destruction of the elastic tissue in the wall of an aneurysm. An analysis of the physical factors influencing whether an aneurysm ruptures showed that the probability of rupture increases with an increase in intra-aneurysmal pressure, an increase in aneurysmal size, a decrease in the minimum wall thickness of an aneurysm, or a decrease in the strength of its structural components.