COMPUTER MODELING OF INTRACRANIAL SACCULAR AND LATERAL ANEURYSMS FOR THE STUDY OF THEIR HEMODYNAMICS

THERE IS STRONG evidence indicating hemodynamic stress as an underlyin g cause for saccular intracranial aneurysm growth, thrombosis, and/or rupture. We examined flow fields encountered in models of cerebral ane urysms having a lateral (originating from the side of an artery, not a t a branch paint) geometric configuration. Shear stress and pressure g radients acting on aneurysm walls under a variety of flow and geometri c conditions were evaluated. For this purpose, a two-dimensional finit e-element computer model of lateral aneurysms in a steady-flow state w as developed. Three idealized aneurysm shapes were studied, half-spher ical, spherical, and pear-shaped. The ostium width of the cerebral ane urysm, relative to the radius of the parent artery and the Reynolds nu mber, were also varied. Maximal shear stresses and maximum pressures ( for an ostium width of 2 times the radius of the parent artery) were t ypically found at the downstream site of the ostium, rather than at th e dome of the aneurysm. In general, the highest shear stresses and the lowest pressures (at the distal portion of the ostium) were obtained in the spherical aneurysm, whereas the lowest shear stresses and the h ighest pressures were found in the half-spherical aneurysm. The locati on of maximal stresses (shear and pressure) at the distal region of th e ostium suggests that growth and/or rupture may well proceed from thi s point. Such findings are in contrast to the commonly held opinion th at aneurysm rupture occurs at the dome. Careful pathological investiga tion will need to be performed to clarify this finding. The results of this preliminary investigation also indicate that the flow field in l ateral aneurysms is highly dependent on a number of factors related to flow and geometric parameters. Geometry seems to be a significant med iator of local magnitudes of stress. Thus, the tendency for growth or thrombosis may be influenced by variations in size or shape.