Stimulated by a recent controversy regarding pressure drops predicted in a giant aneurysm with a proximal stenosis, the present study sought to assess variability in the prediction of pressures and flow by a wide variety of research groups. In phase I, lumen geometry, flow rates, and fluid properties were specified, leaving each research group to choose their solver, discretization, and solution strategies. Variability was assessed by having each group interpolate their results onto a standardized mesh and centerline. For phase II, a physical model of the geometry was constructed, from which pressure and flow rates were measured. Groups repeated their simulations using a geometry reconstructed from a micro-computed tomography (CT) scan of the physical model with the measured flow rates and fluid properties. Phase I results from 25 groups demonstrated remarkable consistency in the pressure patterns, with the majority predicting peak systolic pressure drops within 8% of each other. Aneurysm sac flow patterns were more variable with only a few groups reporting peak systolic flow instabilities owing to their use of high temporal resolutions. Variability for phase II was comparable, and the median predicted pressure drops were within a few millimeters of mercury of the measured values but only after accounting for submillimeter errors in the reconstruction of the life-sized flow model from micro-CT. In summary, pressure can be predicted with consistency by CFD across a wide range of solvers and solution strategies, but this may not hold true for specific flow patterns or derived quantities. Future challenges are needed and should focus on hemodynamic quantities thought to be of clinical interest.

Retrospective morphological and hemodynamic analysis point to a dichotomy between sidewall and bifurcation aneurysms with respect to performance of shape and size parameters in identifying rupture status, suggesting the need for aneurysm type-based analyses in future studies. The current most commonly used clinical risk assessment metric, D(max), was found to be of no value in differentiating between ruptured and unruptured bifurcation aneurysms.

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Background and Purpose The middle cerebral artery (MCA) bifurcation is a preferred site for aneurysm formation. Wider bifurcations angles have been correlated with increased risk of aneurysm formation. We hypothesized a link between the presence of MCA aneurysms and the angle morphology of the bifurcation. Methods 3D rotational angiography volumes of 146 MCA bifurcations (62 aneurysmal) were evaluated for angle morphology: parent-daughter angles (larger daughter-Φ1, smaller daughter-Φ2), bifurcation angle (Φ1+Φ2), and inclination angle (γ) between the parent vessel axis and the plane determined by daughter vessels axes. Statistics were evaluated using Wilcoxon rank-sum analysis and area under the ROC curve (AUC). Results Aneurysmal bifurcations had wider inclination angle γ (median 57.8° vs. 15.4°; p<0.0001). 75% of aneurysmal MCAs had γ>10°, compared to 25% non-aneurysmal. Φ1, Φ2, but especially Φ1+Φ2 were significantly larger in aneurysmal bifurcations (median 171.3° vs. 98.1°; p<0.0001). 67% of aneurysmal bifurcations had Φ1+Φ2>161°, compared to 0% non-aneurysmal MCAs. An optimal threshold of 140° was established for Φ1+Φ2 (AUC=0.98). 68% of aneurysms originating off the daughter branches. 76% of them originated off the branch with the largest branching angle, specifically if this was the smaller daughter branch. Wider Φ1+Φ2 correlated with aneurysm neck width, but not dome size. Conclusion MCA bifurcations harboring aneurysms have significantly larger branching angles, and more often originate off of the branch with the largest angle. Wider inclination angle is strongly correlated with aneurysm presence, a novel finding. The results point to altered WSS regulation as a possible factor in aneurysm development and progression.