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BACKGROUND Thin-walled regions (TWRs) of aneurysm surfaces observed in microscopic surgery are thought to be vulnerable areas for growth and rupture of unruptured intracranial aneurysms (UIAs). OBJECTIVE To identify hemodynamic features of TWRs of aneurysms by using computational fluid dynamics (CFD) analyses of unruptured middle cerebral artery bifurcation (MCAB) aneurysms. METHODS Nine patients with 11 MCAB aneurysms were enrolled, and their TWRs were identified. CFD analysis was performed using 3 parameters: pressure, wall shear stress (WSS), and WSS divergence (WSSD). Each parameter was evaluated for its correspondence with TWR. RESULTS Among 11 aneurysms, 15 TWRs were identified. Corresponding matches with CFD parameters (pressure, WSS, and WSSD) were 73.33, 46.67, and 86.67%, respectively. CONCLUSION WSSD, a hemodynamic parameter that accounts for both magnitude and directionality of WSS, showed the highest correspondence. High WSSD might correspond with TWR of intracranial aneurysms, which are likely high-risk areas for rupture.