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.