ABSTRACT Intracranial aneurysm, a localized dilation of arterial blood vessels in the Circle of Willis and its branches, is potentially life threatening, due to massive bleeding in the subarachnoid space upon rupture. In clinical practice, one minimally invasive surgical procedure is the implantation of a metallic stent to cover the aneurysm neck. This flow diverting device can reduce the flow into the aneurysm and enhance the prospect of thrombosis, a condition expected to reduce the risk of growth and rupture. The biomechanical and haemo-dynamic factors in stented and nonstented situations are studied by computational fluid dynamics. Unlike earlier models with straight or curved parent blood vessels, the aneurysm is now located near an arterial bifurcation. The influence of the aspect (depth to neck) ratio of the aneurysm on the flow dynamics will be emphasized, especially in the post-operation stages. More precisely, the maximum flow velocity, the variations of wall shear stress, the risk of stent migration and volumetric flow rate after endovascular treatment will be studied. Aneurysms with larger aspect ratios (i.e. smaller neck sizes for constant depth) generally pose a greater risk in terms of these flow parameters. These results will assist the applications and design of stents in future neurosurgical therapy. The approach is limited to a nonelastic model, without taking into account of questions like stent expansion and interaction with tissue.
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Tang, A. , Lai, S. , Leung, K. , Leung, G. and Chow, K. (2012) Influence of the aspect ratio on the endovascular treatment of intracranial aneurysms: A computational investigation. Journal of Biomedical Science and Engineering, 5, 422-431. doi: 10.4236/jbise.2012.58054.
 Schievink, W.I. (1997) Medical progress–intracranial aneurysms. New England Journal of Medicine, 336, 28-40.
 Sekhar, L.N. and Heros, R.C. (1981) Origin, growth, and rupture of saccular aneurysms: a review. Neurosurgery, 8, 248-260.
 Rinkel, G.J.E., Djibuti, M., Algra, A. and van Gijn, J. (1998) Prevalence and risk of rupture of intracranial aneurysms: a systematic review. Stroke, 29, 251-256.
 Linn, F.H.H., Rinkel, G.J.E., Algra, A. and van Gijn, J. (1996) Incidence of subarachnoid hemorrhage: role of region, year, and rate of computed tomography: a meta-analysis. Stroke, 27, 625-629.
 Guglielmi, G., Vinuela, F., Dion, J. and Duckwiler, G. (1991) Electrothrombosis of saccular aneurysms via endovascular approach. Part 2: preliminary clinical experience. Journal of Neurosurgery, 75, 8-14.
 Molyneux, A.J., Kerr, R.S.C., Yu, L.M., Clarke, M., Sneade, M., Yarnold, J.A. and Sandercock, P. (2005) International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised comparison of effects on survival, dependency, seizures, rebleeding, subgroups, and aneurysm occlusion. Lancet, 366, 809-817.
 Pierot, L. (2011) Flow diverter stents in the treatment of intracranial aneurysms: where are we? Journal of Neuroradiology, 38, 40-46.
 Wanke, I. and Forsting, M. (2008) Stents for intracranial wide-necked aneurysms: more than mechanical protection. Neuroradiology, 50, 991-998.
 Lasheras, J. C. (2007) The biomechanics of arterial aneurysms. Annual Review of Fluid Mechanics, 39, 293-319.
 Humphrey, J.D. and Taylor, C.A. (2008) Intracranial and abdominal aortic aneurysms: similarities, differences, and need for a new class of computational models. Annual Review of Biomedical Engineering, 10, 221-246.
 Sforza, D.M., Putman, C.M. and Cebral, J.R. (2009) Hemodynamics of cerebral aneurysms. Annual Review of Fluid Mechanics, 41, 91-107.
 Yu, S.C.M. and Zhao, J.B. (1999) A steady flow analysis on the stented and non-stented sidewall aneurysm models. Medical Engineering & Physics, 21, 133-141.
 Liou, T.M., Liou, S.N. and Chu, K.L. (2004) Intra-aneurysmal flow with helix and mesh stent placement across side-wall aneurysm pore of a straight parent vessel. ASME Journal of Biomechanical Engineering, 126, 36-43.
 Liou, T.M. and Li, Y.C. (2008) Effects of stent porosity on hemodynamics in a sidewall aneurysm model. Journal of Biomechanics, 41, 1174-1183.
 Meng, H., Wang, Z., Kim, M., Ecker, R.D. and Hopkins, L.N. (2006) Saccular aneurysms on straight and curved vessels are subject to different hemodynamics: implications of intravascular stenting. American Journal of Neuroradiology, 27, 1861-1865.
 Chow, M.M., Woo, H.H., Masaryk, T.J. and Rasmussen, P.A. (2004) A novel endovascular treatment of a wide-necked basilar apex aneurysm by using a Y-configuration, double stent technique. American Journal of Neuroradiology, 25, 509-512.
 Cekirge, H.S., Yavuz, K., Geyik, S. and Saatci, I. (2011) A novel “Y” stent flow diversion technique for the endovascular treatment of bifurcation aneurysms without endosaccular coiling. American Journal of Neuroradiology, 32, 1262-1268.
 Ujiie, H., Tachibana, H., Hiramatsu, O., Hazel, A.L., Matsumoto, T., Ogasawara, Y., Nakajima, H., Hori, T., Takakura, K. and Kajiya, F. (1999) Effects of size and shape (aspect ratio) on the hemodynamics of saccular aneurysms: a possible index for surgical treatment of intracranial aneurysms. Neurosurgery, 45, 119-130.
 Ujiie, H., Tamano, Y., Sasaki, K. and Hori, T. (2001) Is the aspect ratio a reliable index for predicting the rupture of a saccular aneurysm? Neurosurgery, 48, 495-503.
 Nader-Sepahi, A., Casimiro, M., Sen, J. and Kitchen, N.D. (2004) Is aspect ratio a reliable predicator of intracranial aneurysm rupture? Neurosurgery, 54, 1343-1348.
 Kelly, M.E., Turner IV, R.D., Moskowitz, S.I., Gonugunta, V., Hussain, M.S. and Fiorella, D. (2008) Delayed migration of a self-expanding intracranial microstent. American Journal of Neuroradiology, 29, 1959-1960.
 Pavlisa, G., Ozretic, D., Rados, M. and Pavlisa, G. (2009) Migration of enterprise stent in treatment of intracranial aneurysms: a report of two cases. Radiology and Oncology, 43, 233-239.
 Lobotesis, K., Gholkar, A. and Jayakrishnan, V. (2010) Early migration of a self expanding intracranial stent: case report. Neurosurgery, 67, E516-E517.
 Hampton, T., Walsh, D., Tolias, C. and Fiorella, D. (2011) Mural destabilization after aneurysm treatment with a flow-diverting device: a report of two cases. Journal of Neurointerventional Surgery, 3, 167-171.
 Turowski, B., Macht, S., Kulcsár, Z., Hanggi, D. and Stummer, W. (2011) Early fatal hemorrhage after endovascular cerebral aneurysm treatment with a flow diverter (SILK-stent): do we need to rethink our concepts? Neuroradiology, 53, 37-41.
 Kulcsár, Z., Houdart, E., Bonafé, A., Parker, G., Millar, J., Goddard, A.J.P., Renowden, S., Gál, G., Turowski, B., Mitchell, K., Gray, F., Rodriguez, M., van den Berg, R., Gruber, A., Desal, H., Wanke, I. and Rüfenacht, D.A. (2011) Intra-aneurysmal thrombosis as a possible cause of delayed aneurysm rupture after flow-diversion treatment. American Journal of Neuroradiology, 32, 20-25.
 Hu, J., Zhang, E.Y., Wu, J., Xu, W.L., Chen, H.Q., Shi, Y.K. and Guo, Y.Q. (2010) Pressure shift mediated anoikis of endothelial cell in the flow field in vitro. Journal of Biomedical Science and Engineering, 3, 206-212.
 Fung, G.S.K., Lam, S.K., Cheng, S.W.K. and Chow, K.W. (2008) On stent-graft models in thoracic aortic endovascular repair: a computational investigation of the hemodynamic factors. Computers in Biology and Medicine, 38, 484-489.
 Cheng, S.W.K., Lam, E.S.K., Fung, G.S.K., Ho, P., Ting, A.C.W. and Chow, K.W. (2008) A computational fluid dynamic study of stent graft remodeling after endovascular repair of thoracic aortic dissections. Journal of Vascular Surgery, 48, 303-310.
 Ford, M.D., Lee, S.W., Lownie, S.P., Holdsworth, D.W. and Steinman, D.A. (2008) On the effect of parent-aneurysm angle on flow patterns in basilar tip aneurysms: towards a surrogate geometric marker of intra-aneurismal hemodynamics. Journal of Biomechanics, 41, 241-248.
 Ujiie, H., Shinohara, C., Higa, T., Kato, K., Yoshimoto, S. and Hori, T. (2009) Intraaneurysmal flow and aspect ratio (Dome/Neck). Journal of Biorheology, 23, 41-48.
 Wang, S., Ding, G., Zhang, Y. and Yang, X. (2011) Computational haemodynamics in two idealised cerebral wide-necked aneurysms after stent placement. Computer Methods in Biomechanics and Biomedical Engineering, 14, 927-937.
 Babiker, M.H., Gonzalez, L.F., Ryan, J., Albuquerque, F., Collins, D., Elvikis, A. and Frakes, D.H. (2012) Influence of stent configuration on cerebral aneurysm fluid dynamics. Journal of Biomechanics, 45, 440-447.
 Perktold, K., Kenner, T., Hilbert, D., Spork, B. and Florian, H. (1988) Numerical blood flow analysis: arterial bifurcation with a saccular aneurysm. Basic Research in Cardiology, 83, 24-31.
 Fung, Y.C. (1997) Biomechanics: Circulation. 2nd Edition, Springer, New York.
 Sweetman, B., Xenos, M., Zitella, L. and Linninger, A.A. (2011) Three-dimensional computational prediction of cerebrospinal fluid flow in the human brain. Computers in Biology and Medicine, 41, 67-75.
 Fan, Y., Cheng, S.W.K., Qing, K.X. and Chow, K.W. (2010) Endovascular repair of type B aortic dissection: a study by computational fluid dynamics. Journal of Biomedical Science and Engineering, 3, 900-907.
 Malek, A.M., Alper, S.L. and Izumo, S. (1999) Hemodynamic shear stress and its role in atherosclerosis. Journal of the American Medical Association, 282, 2035-2042.
 Shojima, M., Oshima, M., Takagi, K., Torii, R., Hayakawa, M., Katada, K., Morita, A. and Kirino, T. (2004) Magnitude and role of wall shear stress on cerebral aneurysm: computational fluid dynamic study of 20 middle cerebral artery aneurysms. Stroke, 35, 2500-2505.
 Boussel, L., Rayz, V., McCulloch, C., Martin, A., Acevedo-Bolton, G., Lawton, M., Higashida, R., Smith, W.S., Young, W.L. and Saloner, D. (2008) Aneurysm growth occurs at region of low wall shear stress: patient-specific correlation of hemodynamics and growth in a longitudinal study. Stroke, 39, 2997-3002.