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      Hemodynamic Analysis of Intracranial Aneurysms with Daughter Blebs

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          Background and Purpose: Intracranial aneurysms with daughter blebs appear to have a higher risk of rupture. Whether hemodynamic factors are involved in this phenomenon is not clear. Methods: 54 patient-specific aneurysms harboring 69 daughter blebs were divided into ruptured and unruptured groups based on their clinical history. Realistic models were retrospectively constructed and analyzed by a computational fluid dynamic method. Results: There were no differences in the aspect ratio and morphology type of the aneurysms, the size of blebs or other common risk factors between the two groups. The wall shear stress (WSS) was significantly lower while the oscillatory shear index (OSI) was higher in the daughter blebs than in the primary aneurysms. Bleb-bearing aneurysms with a rupture history displayed significantly lower WSS in the daughter bleb. Of the daughter blebs, 73.9% were localized to the impingement region of the inflow jet. Conclusion: These observations indicate that low WSS and high OSI in the daughter blebs might be involved in increasing the risk of rupture. The localized striking force caused by inflow jets may contribute to the development of daughter blebs. However, a precise role of hemodynamics in predicting the future rupture of daughter blebs needs further study.

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          Most cited references 46

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          Hemodynamic shear stress and its role in atherosclerosis.

           Adel Malek (1999)
          Atherosclerosis, the leading cause of death in the developed world and nearly the leading cause in the developing world, is associated with systemic risk factors including hypertension, smoking, hyperlipidemia, and diabetes mellitus, among others. Nonetheless, atherosclerosis remains a geometrically focal disease, preferentially affecting the outer edges of vessel bifurcations. In these predisposed areas, hemodynamic shear stress, the frictional force acting on the endothelial cell surface as a result of blood flow, is weaker than in protected regions. Studies have identified hemodynamic shear stress as an important determinant of endothelial function and phenotype. Arterial-level shear stress (>15 dyne/cm2) induces endothelial quiescence and an atheroprotective gene expression profile, while low shear stress (<4 dyne/cm2), which is prevalent at atherosclerosis-prone sites, stimulates an atherogenic phenotype. The functional regulation of the endothelium by local hemodynamic shear stress provides a model for understanding the focal propensity of atherosclerosis in the setting of systemic factors and may help guide future therapeutic strategies.
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            Hemodynamic-morphologic discriminants for intracranial aneurysm rupture.

            the purpose of this study was to identify significant morphological and hemodynamic parameters that discriminate intracranial aneurysm rupture status using 3-dimensional angiography and computational fluid dynamics. one hundred nineteen intracranial aneurysms (38 ruptured, 81 unruptured) were analyzed from 3-dimensional angiographic images and computational fluid dynamics. Six morphological and 7 hemodynamic parameters were evaluated for significance with respect to rupture. Receiver operating characteristic analysis identified area under the curve (AUC) and optimal thresholds separating ruptured from unruptured aneurysms for each parameter. Significant parameters were examined by multivariate logistic regression analysis in 3 predictive models-morphology only, hemodynamics only, and combined-to identify independent discriminants, and the AUC receiver operating characteristic of the predicted probability of rupture status was compared among these models. morphological parameters (size ratio, undulation index, ellipticity index, and nonsphericity index) and hemodynamic parameters (average wall shear stress [WSS], maximum intra-aneurysmal WSS, low WSS area, average oscillatory shear index, number of vortices, and relative resident time) achieved statistical significance (P<0.01). Multivariate logistic regression analysis demonstrated size ratio to be the only independently significant factor in the morphology model (AUC, 0.83; 95% CI, 0.75 to 0.91), whereas WSS and oscillatory shear index were the only independently significant variables in the hemodynamics model (AUC, 0.85; 95% CI, 0.78 to 0.93). The combined model retained all 3 variables, size ratio, WSS, and oscillatory shear index (AUC, 0.89; 95% CI, 0.82 to 0.96). all 3 models-morphological (based on size ratio), hemodynamic (based on WSS and oscillatory shear index), and combined-discriminate intracranial aneurysm rupture status with high AUC values. Hemodynamics is as important as morphology in discriminating aneurysm rupture status.
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              Magnitude and role of wall shear stress on cerebral aneurysm: computational fluid dynamic study of 20 middle cerebral artery aneurysms.

              Wall shear stress (WSS) is one of the main pathogenic factors in the development of saccular cerebral aneurysms. The magnitude and distribution of the WSS in and around human middle cerebral artery (MCA) aneurysms were analyzed using the method of computed fluid dynamics (CFD). Twenty mathematical models of MCA vessels with aneurysms were created by 3-dimensional computed tomographic angiography. CFD calculations were performed by using our original finite-element solver with the assumption of Newtonian fluid property for blood and the rigid wall property for the vessel and the aneurysm. The maximum WSS in the calculated region tended to occur near the neck of the aneurysm, not in its tip or bleb. The magnitude of the maximum WSS was 14.39+/-6.21 N/m2, which was 4-times higher than the average WSS in the vessel region (3.64+/-1.25 N/m2). The average WSS of the aneurysm region (1.64+/-1.16 N/m2) was significantly lower than that of the vessel region (P<0.05). The WSSs at the tip of ruptured aneurysms were markedly low. These results suggest that in contrast to the pathogenic effect of a high WSS in the initiating phase, a low WSS may facilitate the growing phase and may trigger the rupture of a cerebral aneurysm by causing degenerative changes in the aneurysm wall. The WSS of the aneurysm region may be of some help for the prediction of rupture.

                Author and article information

                Eur Neurol
                European Neurology
                S. Karger AG
                December 2011
                29 November 2011
                : 66
                : 6
                : 359-367
                aBeijing Neurosurgical Institute, Beijing Tiantan Hospital and bDepartment of Biomedical Engineering, Capital Medical University, Beijing, cDepartment of Mechanics and Engineering Science, Fudan University, Shanghai, and dKey Laboratory of Cardiovascular Remodeling and Function Research, Medical School and Qilu Hospital, Shandong University, Jinan, China
                Author notes
                *S. Mu, MD, PhD and X. Yang, MD, PhD, Beijing Neurosurgical Institute, Beijing Tiantan Hospital, Capital Medical University, Tiantan Xili 6, Chongwen District, Beijing 100050 (China), Tel. +86 10 6709 8852, E-Mail and
                332814 Eur Neurol 2011;66:359–367
                © 2011 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 4, Pages: 9
                Original Paper


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