Vorschlag zweier verschiedener hämodynamischer Mechanismen der Aneurysmagenese basierend auf der Trägergefäß-Bifurkationsgeometrie bei MCA-Aneurysmen

Hemodynamic mechanisms for the initiation of intracranial aneurysms are not completely understood yet. Computational Fluid Dynamics (CFD) provides a powerful tool to investigate hemodynamic features of aneurysms and parent vessel geometries underlying aneurysm initiation, growth and rupture.

We investigated 22 aneurysm-bearing MCA bifurcations and 26 aneurysm-free MCA bifurcations from 42 patients from our institute's database. Based on 3D-DSA imaging, aneurysms were digitally removed from the bifurcation to reconstruct the aneurysm-free parent vessel geometry based on a previously described workflow (Ford et al. 2009). After 3D reconstruction of geometries using AMIRA (FEI Visualization Sciences, France) and definition of boundary conditions, CFD calculations were performed using ANSYS CFX (Ansys Inc., USA). Rigid walls and pulsatile flow conditions were assumed. Blood was modeled as a non-Newtonian fluid with a shear-dependent dynamic viscosity following a Power Law model. Bifurcations were grouped based on geometric features and bifurcation angles into three groups (Type 1 – 3). To assess rupture risks and the probability of these bifurcation types to bear an aneurysm, additional CTA-imaging leading to a total of 99 MCA bifurcations from 72 patients was analyzed as well as clinical data.

We found two different hemodynamic mechanisms based on the geometry of the parent vessel bifurcation. Depending on the bifurcation geometry, one mechanism might be represented by a dislocated flow impingement point due to an asymmetry of the aneurysm bearing bifurcation (Type 1 bifurcations), another by a rotatory flow component (Type 2 bifurcations). Including the CTA-group, different types of bifurcations showed different probabilities to bear an aneurysm. Aneurysms showed different rupture risks depending on the bifurcation type.

We propose three types of MCA-bifurcations based on the parent vessel bifurcation geometry leading to two different hemodynamic patterns in aneurysm-bearing bifurcations. These data might help to better understand hemodynamic mechanisms underlying the formation and growth of MCA aneurysms. Further prospective CFD studies are needed to assess the reproducibility of these findings.