The importance of parent artery geometry 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
References (29)
- et al.
Patient-specific computational modeling of cerebral aneurysms with multiple avenues of flow from 3D rotational angiography images
Acad Radiol
(2006) - et al.
A steady flow analysis on the stented and non-stented sidewall aneurysm models
Med Eng Phys
(1999) - et al.
Computer modeling of intracranial saccular and lateral aneurysms for the study of their hemodynamics
Neurosurgery
(1995) - et al.
Remodeling of saccular cerebral artery aneurysm wall is associated with rupture: Histological analysis of 24 unruptured and 42 ruptured cases
Stroke
(2004) - et al.
Saccular aneurysm formation in curved and bifurcating arteries
AJNR Am J Neuroradiol
(1999) - et al.
A proposed parent vessel geometry-based categorization of saccular intracranial aneurysms: computational flow dynamics analysis of the risk factors for lesion rupture
J Neurosurg
(2005) - et al.
Computational replicas: anatomic reconstructions of cerebral vessels as volume numerical grids at three-dimensional angiography
AJNR Am J Neuroradiol
(2004) - et al.
Effects of arterial geometry on aneurysm growth: three-dimensional computational fluid dynamics study
J Neurosurg
(2004) - et al.
Aneurysm flow dynamics: alterations of slipstream flow for neuroendovascular treatment with liquid embolic agents
AJNR Am J Neuroradiol
(2003) Unruptured intracranial aneurysms: natural history, clinical outcome, and risks of surgical and endovascular treatment
Lancet
(2003)
Factors affecting formation and growth of intracranial aneurysms
Stroke
A technique for improved quantitative characterization of intracranial aneurysms
AJNR Am J Neuroradiol
Structural fragility and inflammatory response of ruptured cerebral aneurysms: A comparative study between ruptured and unruptured cerebral aneurysms
Stroke
Endovascular treatment of wide-necked aneurysms by using two microcatheters: techniques and outcomes in 25 patients
AJNR Am J Neuroradiol
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