Wall Shear Stress Area Research Articles

Development of a computational model for macroscopic predictions of device-induced thrombosis.

While cardiovascular device-induced thrombosis is associated with negative patient outcomes, the convoluted nature of the processes resulting in a thrombus makes the full thrombotic network too computationally expensive to simulate in the complex geometries and flow fields associated with devices. A macroscopic, continuum computational model is developed based on a simplified network, which includes terms for platelet activation (chemical and mechanical) and thrombus deposition and growth in regions of low wall shear stress (WSS). Laminar simulations are performed in a two-dimensional asymmetric sudden expansion geometry and compared with in vitro thrombus size data collected using whole bovine blood. Additionally, the predictive power of the model is tested in a flow cell containing a series of symmetric sudden expansions and contractions. Thrombi form in the low WSS area downstream of the asymmetric expansion and grow into the nearby recirculation region, and thrombus height and length largely remain within 95% confidence intervals calculated from the in vitro data for 30min of blood flow. After 30min, predicted thrombus height and length are 0.94 and 4.32 (normalized by the 2.5mm step height). Importantly, the model also correctly predicts locations of thrombus deposition observed in the in vitro flow cell of expansions and contractions. As the simulation results, which rely on a greatly reduced model of the thrombotic network, are still able to capture the macroscopic behavior of the full network, the model shows promise for timely predictions of device-induced thrombosis toward optimizing and expediting the device development process.

Characteristic analysis of hemodynamics for trunk aneurysm of posterior communicating artery

Objective To study the hemodynamic characteristics of the difference between the trunk aneurysm of posterior communicating artery (PCoA) and the internal carotid artery (ICA)-PCoA aneurysm. Methods A total of 15 patients with trunk aneurysm of PCoA (11 ruptured aneurysms, 4 unruptured aneurysms, for short PCoA trunk group) treated at the Department of Interventional Neuroradiology, Beijing Tiantan Hospital, Capital Medical University from January 2014 to June 2015 were studied retrospectively. The 15 patients with ICA-PCoA aneurysm with approximately the same size and the same rupture state at the same time were used as a matched control group. A numerical simulation analysis was conducted for individual three-dimensional digital subtraction angiography (DSA) images of the patients using the method of computational fluid dynamics. The differences of hemodynamic parameters of the aneurysms were compared between the 2 groups. Results The PCoA trunk aneurysms were in accordance with the blood flow pattern of the lateral aneurysms, and the ICA-PCoA aneurysms were in accordance with the flow blood pattern of the aneurysms at the bifurcations. The hemodynamic parameters in the PCoA trunk group vs. the control group: The wall shear stress (WSS) of the PCoA trunk group and the control group was 0.48±0.08 and 0.63±0.07 respectively. The percentage of the low WSS area (LSA) was 23.20±6.94% and 4.50±2.29% respectively. There were significant differences (P=0.022, P=0.008). The oscillatory shear index (OSI) of the two groups was 0.0233±0.0071 and 0.0158±0.0044 respectively. There was no significant difference (P=0.411). The WSS of the ruptured group (n=22) and the unruptured group (n=8) was 0.45±0.05 and 0.84±0.08 respectively, and LSA was 18.22±5.11% and 1.84±1.76% respectively. There was significant difference (P<0.001, P=0.006). The OSI of the two groups was 0.0234±0.0054 and 0.0091±0.0027 respectively. There was no significant difference (P=0.132). Conclusion The low WSS may be one of the reasons for the high risk of PCoA trunk aneurysm rupture. Key words: Intracranial aneurysms; Aneurysm, ruptured; Hemodynamics; Posterior communicating artery; Computational fluid dynamics

Morphological and Hemodynamic Discriminators for Rupture Status in Posterior Communicating Artery Aneurysms.

Background and PurposeThe conflicting findings of previous morphological and hemodynamic studies on intracranial aneurysm rupture may be caused by the relatively small sample sizes and the variation in location of the patient-specific aneurysm models. We aimed to determine the discriminators for aneurysm rupture status by focusing on only posterior communicating artery (PCoA) aneurysms.Materials and MethodsIn 129 PCoA aneurysms (85 ruptured, 44 unruptured), clinical, morphological and hemodynamic characteristics were compared between the ruptured and unruptured cases. Multivariate logistic regression analysis was performed to determine the discriminators for rupture status of PCoA aneurysms.ResultsWhile univariate analyses showed that the size of aneurysm dome, aspect ratio (AR), size ratio (SR), dome-to-neck ratio (DN), inflow angle (IA), normalized wall shear stress (NWSS) and percentage of low wall shear stress area (LSA) were significantly associated with PCoA aneurysm rupture status. With multivariate analyses, significance was only retained for higher IA (OR = 1.539, p < 0.001) and LSA (OR = 1.393, p = 0.041).ConclusionsHemodynamics and morphology were related to rupture status of intracranial aneurysms. Higher IA and LSA were identified as discriminators for rupture status of PCoA aneurysms.

Hemodynamic and morphological characteristics of unruptured posterior communicating artery aneurysms with oculomotor nerve palsy.

OBJECT Unruptured posterior communicating artery (PCoA) aneurysms with oculomotor nerve palsy (ONP) have a very high risk of rupture. This study investigated the hemodynamic and morphological characteristics of intracranial aneurysms with high rupture risk by analyzing PCoA aneurysms with ONP. METHODS Fourteen unruptured PCoA aneurysms with ONP, 33 ruptured PCoA aneurysms, and 21 asymptomatic unruptured PCoA aneurysms were included in this study. The clinical, morphological, and hemodynamic characteristics were compared among the different groups. RESULTS The clinical characteristics did not differ among the 3 groups (p > 0.05), whereas the morphological and hemodynamic analyses showed that size, aspect ratio, size ratio, undulation index, nonsphericity index, ellipticity index, normalized wall shear stress (WSS), and percentage of low WSS area differed significantly (p < 0.05) among the 3 groups. Furthermore, multiple comparisons revealed that these parameters differed significantly between the ONP group and the asymptomatic unruptured group and between the ruptured group and the asymptomatic unruptured group, except for size, which differed significantly only between the ONP group and the asymptomatic unruptured group (p = 0.0005). No morphological or hemodynamic parameters differed between the ONP group and the ruptured group. CONCLUSIONS Unruptured PCoA aneurysms with ONP demonstrated a distinctive morphological-hemodynamic pattern that was significantly different compared with asymptomatic unruptured PCoA aneurysms and was similar to ruptured PCoA aneurysms. The larger size, more irregular shape, and lower WSS might be related to the high rupture risk of PCoA aneurysms.

Influence of the Accuracy of Angiography-Based Reconstructions on Velocity and Wall Shear Stress Computations in Coronary Bifurcations: A Phantom Study.

IntroductionWall shear stress (WSS) plays a key role in the onset and progression of atherosclerosis in human coronary arteries. Especially sites with low and oscillating WSS near bifurcations have a higher propensity to develop atherosclerosis. WSS computations in coronary bifurcations can be performed in angiography-based 3D reconstructions. It is essential to evaluate how reconstruction errors influence WSS computations in mildly-diseased coronary bifurcations. In mildly-diseased lesions WSS could potentially provide more insight in plaque progression.Materials MethodsFour Plexiglas phantom models of coronary bifurcations were imaged with bi-plane angiography. The lumens were segmented by two clinically experienced readers. Based on the segmentations 3D models were generated. This resulted in three models per phantom: one gold-standard from the phantom model itself, and one from each reader. Steady-state and transient simulations were performed with computational fluid dynamics to compute the WSS. A similarity index and a noninferiority test were used to compare the WSS in the phantoms and their reconstructions. The margin for this test was based on the resolution constraints of angiography.ResultsThe reconstruction errors were similar to previously reported data; in seven out of eight reconstructions less than 0.10 mm. WSS in the regions proximal and far distal of the stenosis showed a good agreement. However, the low WSS areas directly distal of the stenosis showed some disagreement between the phantoms and the readers. This was due to small deviations in the reconstruction of the stenosis that caused differences in the resulting jet, and consequently the size and location of the low WSS area.DiscussionThis study showed that WSS can accurately be computed within angiography-based 3D reconstructions of coronary arteries with early stage atherosclerosis. Qualitatively, there was a good agreement between the phantoms and the readers. Quantitatively, the low WSS regions directly distal to the stenosis were sensitive to small reconstruction errors.

Low WSS and High OSI Measured by 3D Cine PC MRI Reflect High Pulmonary Artery Pressures in Suspected Secondary Pulmonary Arterial Hypertension.

Purpose:Institutional Review Board (IRB)-approved prospective study was conducted to test whether objective and quantitative hemodynamic markers wall shear stress (WSS) and oscillatory shear index (OSI) measured by three-dimensional (3D) cine phase-contrast (PC) can reflect pulmonary arterial hypertension (PAH).Patients and Methods:Seventeen consecutive patients of suspected secondary PAH were examined for pulmonary artery pressures (PAPs) with right heart catheterization (RHC) and three-dimensional (3D) cine PC MR. Based on the RHC data, patients were subdivided into two groups of 12 non-PAH (median age of 74.5 years) and 5 PAH (median age of 77 years) patients. Based on 3D cine PC magnetic resonance (MR), hemodynamic parameters including spatially averaged systolic WSS (sWSS), diastolic WSS (dWSS), mean WSS (mWSS), OSI and blood vessel section area (BVSA) at the pulmonary arterial trunk were calculated. Streamline images in the pulmonary arteries were also assessed. All the parameters were compared between non-PAH and PAH groups.Results:sWSS (N/m2) and mWSS (N/m2) of PAH group was lower than that of non-PAH group (0.594 ± 0.067 vs. 0.961 ± 0.590, P = 0.001), (0.365 ± 0.035 vs. 0.489 ± 0.132, P = 0.027). OSI of PAH group was higher than that of non-PAH (0.214 ± 0.026 vs. 0.130 ± 0.046, P = 0.001). sWSS, mWSS, and dWSS were inversely correlated and OSI was positively correlated to mean PAP or systolic PAP with r values of –0.638 (P = 0.005), –0.643 (P = 0.005), –0.485 (P = 0.049), and 0.625 (P = 0.007); or –0.622 (P = 0.008), –0.629 (P = 0.007), –0.484 (P = 0.049), and 0.594 (P = 0.012), respectively. sWSS was also inversely correlated to BVSA with r value of –0.488 (P = 0.049), and OSI was correlated to BVSA with r value of 0.574 (P = 0.016). Vortex or helical flows were observed more frequently in PAH patients.Conclusions:The low sWSS and mWSS as well as high OSI measured with 3D cine PC MR could be potential hemodynamic markers for the increased PAP in suspected secondary PAH patients.

Abstract 17989: Evolution of At-risk Aortic Tissue in Patients With Bicuspid Aortic Valve After Valve or Aorta Replacement

Objectives: Bicuspid aortic valve (BAV) is associated with increased risk of aortopathy requiring surgery. However, to date, there is no clear consensus on aortic resection extent. Our objective was to study in BAV patients the evolution of ascending aortic (AA) ‘at-risk’ tissue, as defined by elevated wall shear stress (WSS) estimated using 4D flow MRI acquired at baseline and follow up. Methods: Eighteen BAV patients (49±15yrs) were included who underwent AA repair and MRI before surgery and at follow up (mean duration: 154±250 [7-977] days). For each patient and exam, 3D aortic systolic WSS was estimated from 4D flow MRI and at-risk tissue area was defined as the treatable region with high WSS, when compared to an atlas of physiologically normal values (as previously established in healthy controls). Results: The baseline sinus of Valsava and mid-AA diameters were both 4.5±0.6cm. Eight patients had severe aortic stenosis or regurgitation. Three patients had aortic valve replacement without aortic resection, 8 had AA repair without hemiarch repair, and 7 had AA and hemiarch repair. In the 8 AA repair patients, 3D area of elevated WSS increased at baseline from 25±29% to 52±37% at follow up, when expressed in percentage of the AA tissue remaining after surgery up from graft to the first branch (Figure). Little change in at-risk tissue area was observed in hemiarch repair patients. Conclusions: Our preliminary study demonstrates feasibility of 4D flow MRI to provide data regarding at-risk aortic tissue progression in BAV patients who underwent AA repair. Larger studies in a variety of clinical conditions are warranted to further understand the implications of these findings.

4D FLOW MRI IDENTIFIES REGIONS OF MORE SEVERE AORTOPATHY IN THE HUMAN BICUSPID AORTA

Patients with congenital bicuspid aortic valves (BAV) are prone to progressive enlargement of the ascending aorta (aortopathy), characterized by medial elastin fiber degradation. We previously demonstrated that non-invasive hemodynamic assessment of regional wall shear stress (WSS) using 4D flow MRI can identify tissue regions with more severe elastin degeneration. The specificity of these observations to regions of high WSS is unclear. In this study, we extend these observations and examined molecular mediators of ECM homeostasis and histopathology in aortic tissue from BAV patients in the context of differential regional hemodynamics. Aortic tissue from regions of normal and elevated WSS (from mean aortic diameter 4.6±0.3 cm; range: 4.0-5.2 cm) was collected from BAV patients (N=17) undergoing ascending aortic surgery and who received pre-operative 4D flow MRI. To determine regions of “normal” and “elevated” WSS, WSS heatmaps of each aorta were constructed relative to the 95% confidence interval for normal physiological WSS values of a tricuspid aortic valve population. Tissue was evaluated for elastin fiber content and architecture (fiber thickness and fiber-to-fiber distance). Mediators of ECM degradation (TGFβ-1, MMPs and TIMPs) were assessed in areas of normal and elevated WSS. MMP-2 concentration was positively correlated with TIMP-2 concentration in all tissues (r=0.744; p<0.0001) independent of regional WSS. However, in samples from regions of elevated WSS, TGFβ-1 concentrations negatively correlated with the amount of elastin fibers (r=-0.548; p=0.053) and concentration of MMP-2 positively correlated with elastin fiber-to-fiber distance (r=0.539; p=0.026). Importantly, no correlations between mediators of ECM degradation and metrics of elastin fiber degradation were observed in adjacent tissue regions subjected to normal WSS. ECM dysregulation in the BAV aorta correlated with aortopathy in areas of elevated WSS but not in adjacent areas of normal WSS. These data further implicate WSS and regional hemodynamics in the expression of human bicuspid aortopathy. 4D flow MRI may be a promising non-invasive imaging tool to guide patient-specific resection strategies given the observed specificity of elevated WSS to predict tissue regions with more severe aortopathy.

Effects of the inlet conditions and blood models on accurate prediction of hemodynamics in the stented coronary arteries

Hemodynamics altered by stent implantation is well-known to be closely related to in-stent restenosis. Computational fluid dynamics (CFD) method has been used to investigate the hemodynamics in stented arteries in detail and help to analyze the performances of stents. In this study, blood models with Newtonian or non-Newtonian properties were numerically investigated for the hemodynamics at steady or pulsatile inlet conditions respectively employing CFD based on the finite volume method. The results showed that the blood model with non-Newtonian property decreased the area of low wall shear stress (WSS) compared with the blood model with Newtonian property and the magnitude of WSS varied with the magnitude and waveform of the inlet velocity. The study indicates that the inlet conditions and blood models are all important for accurately predicting the hemodynamics. This will be beneficial to estimate the performances of stents and also help clinicians to select the proper stents for the patients.

Hemodynamics in growing and stable cerebral aneurysms

ObjectiveThe detailed mechanisms of cerebral aneurysm evolution are poorly understood but are important for objective aneurysm evaluation and improved patient management. The purpose of this study was to identify hemodynamic...

Hemodynamic characteristics of large unruptured internal carotid artery aneurysms prior to rupture: a case control study

ObjectivePost-ruptured intracranial aneurysm geometry models have been widely used in computational fluid dynamic studies to assess hemodynamic parameters associated with aneurysm rupture. However, their results may not be valid due...

MODELING OF SUPERIOR MESENTERIC ARTERY ANEURYSM USING FLUID–STRUCTURE INTERACTION

The aim of this study was to model the blood flow and predict related hemodynamics characteristics in healthy superior mesenteric artery (SMA) and saccular aneurysm cases. A fluid–structure interaction (FSI) method was performed, using an arbitrary Langrangian–Eulerian mesh. The computational mesh was generated using anatomical data from available human computed tomography (CT)-images. Combining constitution and momentum equations, projection method, the discretized resultant equation were numerically solved for velocity, pressure, shear stress and vortices for healthy/aneurysmal artery. The results including velocity contours, pressure contours, shear rate values, and vortices were obtained and analyzed for three main steps including peak systole, diastole, and end of cardiac cycle. Profiles show the varying velocity and pressure for a pulsatile flow input before and after aneurysms. They also show the formation of single or multiple vortices at aneurysmal area and decrease of wall shear stress with aneurysm enlargement. Furthermore, shear rate values at the neck of aneurysms exceed throughout the entire cardiac cycle. The outcome of the computational analysis is then compared to information available on pressure, vortices and wall shear stress from some clinical findings.

RETRACTED: Hemodynamic Features of Unruptured Cerebral Aneurysms before Rupture: A CFD Study

Objective: This study was designed to identify hemodynamic features of aneurysms prior to rupture in comparison with unruptured aneurysms. Materials and Methods: A retrospective data of four large unruptured aneurysms (pre-ruptured group) with sufficient films just pre-rupture was used. Matched with the same location and similar sizes, another four unruptured aneurysms (unruptured group) were in accordance with controls during the same time period and flow simulations were performed for hemodynamic analysis. Results: Compared with the unruptured group, the pre-ruptured group had significantly more irregular aneurysm shape, higher aspect ratio and lower aneurysm-averaged wall shear stress (p = 0.031, p = 0.039 and p = 0.042, respectively). Although pre-ruptured aneurysms had lower low wall shear stress (WSS) area and higher oscillatory shear index value, there was no significant difference between groups. Conclusions: Irregular shape, higher aspect ratio and low wall shear stress were relative with unruptured ICA aneurysms in predicting rupture. Those patients with these risk factors should be more prone to treatment even if with an unruptured aneurysm.

Abstract 14689: Regional Aortic Wall Shear Stress Mapping Implicates Hemodynamics in Human Bicuspid Aortopathy

Introduction: A suspected genetic cause for bicuspid aortic valve (BAV) aortopathy has led to aggressive resection strategies. Using 4D flow MRI, we documented increased regional wall shear stress (WSS) in BAV patients. Local hemodynamics may exacerbate extracellular matrix (ECM) degradation leading to disease progression. If validated, preoperative regional hemodynamic assessment could be used to guide more targeted patient-specific aortic resection. For the first time, we correlated regional WSS with aortic tissue remodeling in BAV patients. Methods &amp; Results: BAV patients (N=11) undergoing ascending aortic resection received preoperative 4D flow MRI with regional WSS differences mapped. Paired aortic wall samples (from same-patient with elevated WSS paired to normal WSS regions) were collected during surgery and compared using histology (pentachrome), biomechanics (biaxial mechanical testing), and ECM regulation (protein expression). Patient mean age: 49±18 years; mean aortic diameter: 4.6±0.7cm (range: 3.6 - 6.3cm); 55% had R+L fusion pattern; 36% had severe aortic stenosis. All patients had heterogeneous WSS patterns with regions of elevated WSS adjacent to those of normal WSS. By histology, regions of increased WSS showed greater medial elastin fragmentation, fibrosis, and cystic medial necrosis compared to adjacent areas of normal WSS. Regions of increased WSS showed increased elastic modulus (fold change±SD: 1.53±0.68; P=0.06, N=5) and collagen stiffness (1.37±0.49; P=0.07, N=5) compared to normal WSS regions suggesting altered distensibility. Multiplex protein analyses of ECM regulatory molecules revealed an increase in transforming growth factor β-1 (1.49±0.71, P=0.02), MMP-1 (1.62±0.84; P=0.01), MMP-2 (1.49±1.00; P=0.06), MMP-3 (1.23±0.36; P=0.02), MMP-7 (1.57±0.75; P=0.02), and TIMP-2 (1.26±0.33; P=0.01) in elevated WSS regions suggesting ECM dysregulation consistent with aortic remodeling. Conclusions: In BAV aorta, regional WSS corresponds with local histologic abnormalities, altered biomechanics, and ECM dysregulation. These novel data strongly implicate local hemodynamics as a mediator of BAV aortopathy. With further validation, 4D flow MRI could be used to guide personalized resection strategies.

Morphological and hemodynamic analysis of posterior communicating artery aneurysms prone to rupture: a matched case–control study

ObjectivesWe evaluated the correlation between posterior communicating artery (PcomA) aneurysm rupture and morphological and hemodynamic parameters to assess related rupture risk indices.MethodsSix patients with PcomA aneurysms that ultimately ruptured (cases)...

Morphologic and hemodynamic risk factors in ruptured aneurysms imaged before and after rupture.

Due to limited information about aneurysm natural history, choosing the appropriate management strategy for an unruptured aneurysm is challenging. By comparing unruptured and ruptured cases, studies have identified a variety of aneurysm morphologic and hemodynamic properties as risk factors for rupture. In this study, we investigated changes in 4 ruptured aneurysms before and after rupture and tested whether previously published risk factors identified a risk before rupture. A retrospective review of ruptured aneurysms based on the inclusion criteria of documenting angiographic images before and after rupture was performed. Such cases are extremely rare. To minimize hemodynamic influence due to location, we selected 4 cases at the posterior communicating artery. 3D morphologic and hemodynamic analyses were applied to examine qualitative and quantitative risk factors in aneurysms before and after rupture. When we compared aneurysms before and after rupture, all increased in size. Volume, surface area, and morphology changed in both high and low wall shear stress areas. Aneurysm surface ratio, nonsphericity index, and pulsatility index were the only risk factors to consistently identify risk before and after aneurysm rupture for all aneurysms. Although changes in shape and flow properties were found before and after aneurysm rupture, in this small study, we found that some risk factors were evident as early as 2 years before rupture.

Solid and Fluid Simulations of Vertebral Artery Stenosis Treated with Stents with Different Shapes of Link

To investigate the effect of endovascular stents with different links on treating stenotic vertebral artery. Three kinds of stent with different links (L-stent, V-stent and S-stent respectively) and idealized stenotic vertebral artery were established. The deployment procedure of stent in the stenotic artery and hemodynamics based on the deformed models were simulated. S-stent comparatively features better flexibility the smallest foreshortening, inducing smaller stress in the stent strut, as well as smaller stress generated in the arterial wall; L-stent comparatively causes smaller area of low wall shear stress, less blood stagnation area and better blood flow close to the artery wall. From the view point of combination of solid mechanics and hemodynamics, S-stent has better therapeutic effect because of its lower potential possibility of inducing ISR, and better prospects in clinical application than L-stent and V-stent.

Hemodynamic Behavior of Coronary Stents in Straight and Curved Arteries

Stents are miniature medical devices that can be inserted into arteries and expanded during angioplasty to restore blood flow and prevent arterial collapse. They have been the primary treatment for cardiovascular diseases since the 1990s. However, after stenting, potential risks associated with restenosis may occur, and several studies have shown that stent design could be one of the critical factors in this process. Computational modeling has been widely used as an important tool to predict the clinical performance of stents and hemodynamic behavior in stented arteries. In this study, computational fluid dynamics models were developed to investigate the effects of cardiovascular stent design on the wall shear stress distribution in straight and curved coronary arteries. Results showed that the stent design pattern alone did not have a significant impact on stent hemodynamics; however, stenting in curved arteries increased the low shear stress area, the region where wall shear stress is less than 5 dynes/cm2, which may lead to a higher restenosis rate. The total surface area of low wall shear stress almost doubled when the angle of artery curvature increased from 0o to 90o. The implication is that stent implantation in a tortuous artery greatly increases the risk of restenosis. The proposed methodology and findings show that the presence of a stent in straight or curved arteries alters the flow field and wall shear stress distribution within arteries, providing great insight for the future design optimization and physician practice to help achieve the best possible clinical outcomes.

Analysis of Morphologic and Hemodynamic Parameters for Unruptured Posterior Communicating Artery Aneurysms with Oculomotor Nerve Palsy

Posterior communicating artery aneurysms with oculomotor nerve palsy may imply sudden enlargement of the aneurysm sac and have a high risk of rupture. Our aim was to identify the morphologic and hemodynamic parameters in this special period of aneurysm progression and to assess related rupture risk indices. We analyzed the morphologic and hemodynamic parameters of 9 unruptured posterior communicating artery aneurysms with oculomotor nerve palsy and 9 ruptured ones. The morphologic parameters were measured and calculated from patient-specific 3D rotational angiographic images, and pulsatile computational fluid dynamic simulation was then performed for hemodynamic parameters. There was no significant statistical difference between the 2 groups in size, aspect ratio, size ratio, aneurysm angle, or vessel angle; analysis only demonstrated a significantly lower wall shear stress of the aneurysm wall in the symptomatic unruptured group in hemodynamics (P = .024), whereas there were no differences in wall shear stress of the parent artery, low wall shear stress area, and oscillatory shear index. From morphologic and hemodynamic perspectives, we demonstrated that posterior communicating artery aneurysms with oculomotor nerve palsy had characteristics similar to those of ruptured ones, except for lower wall shear stress on the aneurysm wall, which might indicate an important role in aneurysm rupture.

Wall shear stress in intracranial aneurysms and adjacent arteries.

Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries.