Background and purpose Hemodynamics is thought to play an important role in the mechanisms of aneurysm pathogenesis, progression and rupture. The purpose of this study was to define quantitative measures related to qualitative flow characteristics previously analyzed and to investigate their relationship to aneurysm rupture. Methods The hemodynamic environments in 210 cerebral aneurysms were analyzed using image-based CFD under different flow conditions. Quantitative hemodynamic variables were defined and extracted from the simulation results. A statistical analysis of the relationship to the previous history of aneurysm rupture was performed, and the variability with flow conditions was assessed. Results Ruptured aneurysms were more likely to have larger inflow concentrations, larger maximum wall shear stress (WSS), larger shear concentrations and lower viscous dissipation ratios than unruptured aneurysms. Areas under low WSS and measures of abnormally low shear force distributions of ruptured and unruptured aneurysms were not statistically different. Although the values of hemodynamic quantities changed with different flow conditions, the statistical differences or ratios between their mean values over the ruptured and unruptured groups were maintained, for both pulsatile and steady flows. Conclusions Concentrated inflow streams and WSS distributions with elevated levels of maximal WSS and low aneurysmal viscous dissipation are statistically associated with a clinical history of prior aneurysm rupture. In contrast, the area and total viscous shear force applied in the aneurysm region subjected to abnormally low WSS levels are not. This study highlights the potential for image-based CFD for investigating aneurysm evolution mechanisms and for clinical assessment of aneurysm risks.

BACKGROUND AND PURPOSE:Flow-diverting approaches to intracranial aneurysm treatment had many promising early results, but recent apparently successful treatments have been complicated by later aneurysm hemorrhage. We analyzed 7 cases of aneurysms treated with flow diversion to explore the possible rupture mechanisms.

Background and purpose Hemodynamic factors are thought to play an important role in the initiation, growth and rupture of cerebral aneurysms. This report describes a study of the associations between qualitative intra-aneurysmal hemodynamics and the rupture of cerebral aneurysms. Methods 210 consecutive aneurysms were analyzed using patient-specific CFD simulations under pulsatile flow conditions. The aneurysms were classified into categories depending on the complexity and stability of the flow pattern, size of the impingement region, and inflow concentration by two blinded observers. A statistical analysis was then performed with respect to history of previous rupture. Inter-observer variability analysis was performed. Results Ruptured aneurysms were more likely to have complex flow patterns (83%, p<0.001), stable flow patterns (75%, p=0.0018), 66% concentrated inflow (66%, p=<0.0001), and small impingement regions (76%, p=0.0006) compared to unruptured aneurysms. Inter-observer variability analyses indicate that all the classifications performed are in very good agreement, i.e. well within the 95% confidence interval. Conclusions A qualitative hemodynamic analysis of cerebral aneurysms using image based patient-specific geometries has shown that concentrated inflow jets, small impingement regions, complex flow patterns, and unstable flow patterns are correlated with a clinical history of prior aneurysm rupture. These qualitative measures provide a starting point for more sophisticated quantitative analysis aimed at assigning aneurysm risk of future rupture. These analyses highlight the potential for CFD to play an important role in the clinical determination of aneurysm risks.

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Characterization of the complex branching architecture of cerebral arteries across a representative sample of the human population is important for diagnosing, analyzing, and predicting pathological states. Brain arterial vasculature can be visualized by magnetic resonance angiography (MRA). However, most MRA studies are limited to qualitative assessments, partial morphometric analyses, individual (or small numbers of) subjects, proprietary datasets, or combinations of the above limitations. Neuroinformatics tools, developed for neuronal arbor analysis, were used to quantify vascular morphology from 3 T time-of-flight MRA high-resolution (620 μm isotropic) images collected in 61 healthy volunteers (36/25 F/M, average age = 31.2 ± 10.7, range = 19–64 years). We present in-depth morphometric analyses of the global and local anatomical features of these arbors. The overall structure and size of the vasculature did not significantly differ across genders, ages, or hemispheres. The total length of the three major arterial trees stemming from the circle of Willis (from smallest to largest: the posterior, anterior, and middle cerebral arteries; or PCAs, ACAs, and MCAs, respectively) followed an approximate 1:2:4 proportion. Arterial size co-varied across individuals: subjects with one artery longer than average tended to have all other arteries also longer than average. There was no net right–left difference across the population in any of the individual arteries, but ACAs were more lateralized than MCAs. MCAs, ACAs, and PCAs had similar branch-level properties such as bifurcation angles. Throughout the arterial vasculature, there were considerable differences between branch types: bifurcating branches were significantly shorter and straighter than terminating branches. Furthermore, the length and meandering of bifurcating branches increased with age and with path distance from the circle of Willis. All reconstructions are freely distributed through a public database to enable additional analyses and modeling (cng.gmu.edu/brava).

The occlusion time of cerebral aneurysms treated with flow diverters can be predicted by the hemodynamic conditions created immediately after device implantation. Specifically, low post-implantation flow velocity, inflow rate, and shear rate are associated with fast occlusion times.

Background and Purpose Saccular intracranial aneurysm (sIA) is a common disease that may cause devastating intracranial hemorrhage. Hemodynamics, wall remodeling, and wall inflammation have been associated with sIA rupture. We investigated how sIA hemodynamics associates with wall remodeling and inflammation of the sIA wall. Methods Tissue samples resected during sIA surgery (11 unruptured, 9 ruptured sIAs) were studied with histology and immunohistochemistry. Patient-specific computational models of hemodynamics were created from preoperative CT-angiographies. Results More stable and less complex flows were associated with thick, hyperplastic sIA walls while slower flows with more diffuse inflow were associated with degenerated and decellularized sIA walls. Wall degeneration (p=0.041) and rupture was associated with increased inflammation (CD45+, p=0.031). High wall shear stress (WSS, p=0.018), higher vorticity (VO, p=0.046), higher viscous dissipation (VD, p=0.046), and high shear rate (SR, p=0.046) associated with increased inflammation. Inflammation was also associated with lack of intact endothelium (p=0.034), and presence of organized luminal thrombosis (p=0.018), although overall organized thrombosis was associated with low minimum WSS (p=0.034) and not with the flow conditions that associated with inflammation. Conclusions Flow conditions in the sIA associate with wall remodeling. Inflammation, which is associated with degenerative wall remodeling and rupture, is associated with high flow activity including elevated WSS. Endothelial injury may be a mechanism by which flow induces inflammation in the sIA wall. Hemodynamic simulations might prove to be useful in identifying sIAs at risk of developing inflammation, a potential biomarker for rupture.

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