Aneurysm　wall　thickness　is　an　important　determinant　of　aneurysm　progression　and　intra-procedural　rupture.　Several　previous　studies　have　evaluated　the　association　between　hemodynamic　stress　and　aneurysm　wall　thickness,　but　conflicting　results　were　obtained　and　no　consensus　has　been　achieved.　According　to　the　intraoperative　findings,　twenty-eight　unruptured　middle　cerebral　artery　(MCA)　aneurysms　presented　with　thin-walled　regions　were　enrolled　in　our　study.　Patient-specific　3D　aneurysm　models　were　constructed　from　preoperative　computed　tomography　angiography　(CTA)　data　and　computational　fluid　dynamics　(CFD)　analyses　were　performed　under　pulsatile-flow　conditions.　Thin　walled　regions　of　aneurysm　dome　were　recognized　by　two　experienced　reviewers　based　on　the　intraoperative　microscopy　findings.　Hemodynamic　parameters　derived　from　CFD　analysis,　including　normalized　wall　shear　stress　(NWSS),　normalized　pressure　(NP),　the　oscillatory　shear　index　(OSI)　and　relative　residence　time　(RRT),　were　compared　between　thin-walled　regions　and　surrounding　normal-thickness　areas.　Of　the　included　aneurysms,　twenty-eight　pairs　of　thin-walled　and　normal　surrounding　regions　were　determined.　Compared　with　surrounding　tissues,　thin-walled　regions　of　aneurysm　wall　tended　to　present　with　higher　pressure　(1.232　vs　1.043,　p　＜0.05)　and　lower　wall　shear　stress　(0.693　vs　0.868,　p　＜0.05).　Multivariate　analysis　revealed　that　elevated　NP　was　significantly　associated　with　thinning　of　the　local　aneurysm　wall.　Higher　pressure　and　lower　WSS　were　characteristic　hemodynamic　features　associated　with　thinner　regions　of　the　aneurysm　wall,　elevated　NP　was　an　independent　risk　factor　for　local　aneurysm　wall　thinning.　CFD　seems　to　be　a　useful　method　to　estimate　the　location　of　thin-walled　region,　which　will　be　helpful　in　reducing　the　risk　of　intraoperative　rupture.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.