The importance of parent artery geometry in intra-aneurysmal hemodynamics

https://doi.org/10.1016/j.medengphy.2007.09.006Get rights and content

Abstract

We show the importance of arterial geometry in intra-aneurysmal hemodynamics. Using a new geometric parameterized saccular aneurysm model including parameters for parent artery shape and the configuration of the aneurysm in the parent artery, we performed a parametric computational fluid dynamics study. We examined lateral saccular aneurysm models with different aneurysm shapes (i.e., the ratio of aneurysm height to aneurysm neck diameter) and different configurations (i.e., the torsion angle of the aneurysm to the upstream part of the parent artery). The aneurysm lateral to the curve of the parent artery had significantly higher wall shear stress than the aneurysm inside or outside the curve of the artery, even with the same shape of the aneurysm. Our findings suggest the important role played by the configuration of the aneurysm relative to the parent artery in intra-aneurysmal hemodynamics.

Introduction

The geometric parameters of saccular cerebral aneurysms have been used as indices to predict aneurysm development and the risk of aneurysm rupture. Some of the most commonly used geometric parameters are aneurysm sac diameter D and aneurysm height H. The ratio of these sizes to the neck diameter N, D/N and H/N, and the ratio of the two sizes D/H have been also reported as geometric parameters [11], [16], [19], [20], [23], [24], [26]. While the clinical treatment of cerebral aneurysms is decided using indices based on these aneurysm geometric parameters, several studies have shown that aneurysms rupture during clinical follow-up [19], [24], [26], implying that these indices do not cover the physiological parameter space fully. New indices for clinical treatment should be defined based on the hypothesis that hemodynamics are involved in the development of aneurysms. From a fluid dynamics perspective, one should include not just the aneurysm shape, but also the parent artery shape and configuration of that aneurysm to the artery. Nevertheless, most clinical studies of ruptured and unruptured aneurysms have not considered parent artery shape or configuration.

In recent years, a large number of computational fluid dynamics (CFD) studies have examined blood flow to clarify the hemodynamics of aneurysms [1], [2], [4], [5], [6], [7], [17], [21], [22], [25]. However, the relationships between the intra-aneurysmal hemodynamics and the geometric parameters are poorly understood, even for geometric parameters of the aneurysm itself. Therefore parametric studies are needed to determine which geometric parameters affect intra-aneurysmal flow. CFD studies can model an aneurysm using an idealized geometry or a realistic geometry. The conventional idealized models [1], [4], [5], [7], [17], [25], which are often expressed by simple shapes such as a sphere or a cylinder, are insufficient to discuss the effect of an individual aneurysm shape parameter on the intra-aneurysmal flow because such models cannot change one parameter without changing others. Moreover, most hemodynamics studies have not considered the parent artery shape and configuration as geometric parameters. To reveal the effects of each geometric parameter, including the aneurysm, parent artery and configuration, parametric studies using simple geometries are more suitable than the realistic models used in previous studies [2], [5], [6], [22].

We present a parametric computational study of blood flow in idealized lateral saccular cerebral aneurysms. A new geometrical modeling method is proposed for describing a wide variety of geometric parameters, including parent artery shape and configuration. Using the proposed models, we show how the configuration of the aneurysm relative to the parent artery can strongly affect intra-aneurysmal flow.

Section snippets

Saccular aneurysm model

This paper focuses on saccular cerebral aneurysms at arterial bends. Such non-branching site aneurysms have been reported clinically [27]. We propose an aneurysm modeling method for expressing a wide variety of geometric parameters for saccular aneurysms. We consider an aneurysm on a curved parent artery with diameter Ø, curvature radius λ and torsion angle of the downstream part to the upstream part γ as illustrated in Fig. 1(a and b). Characteristically, saccular aneurysms consist of a

Results and discussion

Fig. 3 shows the streamlines of the intra-aneurysmal flow, in which the color represents the velocity magnitude. On the distal side of the neck, the fluid particles are divided into downstream and inside the aneurysm. The particles enter the aneurysm circulate several times and then leave the aneurysm. Ujiie et al. [23] observed a double vortex structure for aneurysms placed at the apex of artery bifurcations when H/N > 1.6. The flow pattern in curved artery aneurysms differs from that in

Conclusions

We have presented a parametric computational study of blood flow in saccular cerebral aneurysms using a new lateral saccular aneurysm model. The results clearly suggest the importance of the configuration of the aneurysm relative to the parent artery rather than the shape of the aneurysm in determining intra-aneurysm hemodynamics. To determine new indices for the clinical treatment of aneurysms, a large number of results from both parametric studies and clinical surveys are needed. While

Conflict of interest

This paper has no conflicts of interest.

Acknowledgements

This study was made possible by the following grants: “Revolutionary Simulation Software (RSS21)” project supported by the next-generation IT program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT); Grants-in-Aid for Scientific Research from MEXT and JSPS Scientific Research in Priority Areas (768) “Biomechanics at Micro- and Nanoscale Levels” and Scientific Research(A) No. 6200031 “Mechanism of the formation, destruction, and movement of thrombi responsible for

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