Trends Journal of Sciences Research (2015) 2(2):73-75 http://www.tjsr.org Stresses Variation due to the Anomalies in Circle of Willis Seyed Roholah Ghodsi 1,2 , Vahid Esfahanian 3 , Hadi Dashtaki 4 , Seyed Mohammad Ghodsi 5 1 Assistant professor, Engineering department, Islamic Azad University of Parand, Iran 2 Senior researcher, VFE Research Institute, University of Tehran, Tehran, Iran 3 Professor, School of Mechanical Engineering, University of Tehran, Tehran, Iran 4 Senior Researcher, VFE Research Institute, University of Tehran, Tehran, Iran 5 Associate professor, Sina Trauma Research Center, Tehran University of Medical Science, Tehran, Iran * Correspondence: Seyed Roholah Ghodsi(dr.sr.ghodsi@ut.ac.ir) Abstract The aneurysm is a complex phenomenon which is affected by different factors, such as the biological diseases and the blood flow parameters. The wall shear stress and pressure are the main factors in the establishment and growth of cerebral aneurysm. The circle of Willis is a prevalent location for aneurysm. On the other hand, the anomalies of circle of Willis cause variations in flow field pattern and also the wall shear stress and pressure. In the present study, the effects of some anomalies in the flow pattern are investigated using three dimensional simulation of the Circle of Willis. The simulations are conducted using commercial ANSYS FLUENT. The obtained results show the major anomalies cause increase wall shear stress and pressure on the wall of circle of Willis. This factor can lead to increase the risk of aneurysm. Keywords: Biomechanics, Wall Shear Stress, Circle of Willis, Aneurysm. Citation: Seyed Roholah Ghodsi, Vahid Esfahanian, Hadi Dashtaki, Seyed Mohammad Ghodsi. Stresses Variation due to the Anomalies in Circle of Willis. Trends Journal of Sciences Research. Vol. 2, No. 2, 2015, pp. 50-55. Introduction The Circle of Willis (CoW) is a vital part of cerebrovascular system, which is located at the base of the brain. The CoW is a prevalent location for aneurysm with high mortality risk. About 85% of reported cerebrovascular aneurysms have been observed in the CoW, about 30% in Anterior Communicating Artery (ACoA), 30% in Internal Carotid Artery (ICA) , and 22% in Middle Cerebral Artery (MCA)[1]. The stresses are the known influential factors on aneurysm establishment. The forces on the vessel walls are generated by normal stresses due to blood pressure and shear stress due to blood flow. Therefore, the pressure and flow characteristics, i.e. velocity and direction, have crucial effects on the vessel wall tensions and deformations. The normal stresses due to the blood pressure are transferred to all vessel wall layers (intima, media and adventitia). But, just the inner layer of arterial wall, i.e. the vascular endothelium, is exposed to the Wall Shear Stress (WSS) [2]. Ghodsi et al. proposed the Blood Flow Vectoring Control (BFVC) to change the main form of flow streamlines and the distributions of pressure and WSS using a partial clamp [3]. Very low WSS causes the loss of permeability of the endothelial cell membrane. On the other side, high WSS affects their proliferation and migration and change the endothelial cell expression [4]. Kayembe et al. [5] showed that the variation of CoW is a certain cause of aneurysm development. Lazzaro et al. [6] concluded that the investigation of flow field characteristics can help to identify the effects of variations in the aneurysm development and rupture. Approximately, at least 40 to 50% of the people confront with the CoW’s anomalies [7]. There are different types of CoW anomalies, including: hypoplastic Anterior Communicating Arteries (AcoA), hypoplastic Posterior Communicating Arteries (PcoA), hypoplastic PcoA and AcoA, Bilateral hypoplastic PcoAs and etc [8]. The PCoAs are the prevalent positions of variations. The PCoAs are small or absent in many patients. One fourth of MR angiograms and one third of all anatomic dissections show the hypoplasia of one or both PCoAs [9]. In the current study, the effects of absence of one and both PCoAs in the flow pattern and also the amount of WSS and pressure are investigated. Model Specifications The schematic view of CoW is shown in Figure 1. There are 4 inlets and 6 outlets, including: Vertebral arteries (VA) and Internal Carotid Arteries (ICA) as the inlets and Posterior Cerebral Arteries (PCA), Middle Cerebral Arteries (MCA) and Anterior Cerebral Arteries (ACA) as the outlets. Also there are four communicating arteries, including: PCoAs and ACoAs. The simulation of cerebral blood flow requires consideration of different aspects [10]. In the present study, the simulation is performed in a three-dimensional domain. The unsteady flow field is simulated in a laminar condition. The boundary conditions in inlets and outlets are mass flow and static pressure, respectively. Research Paper Open Access