Hemodynamic characteristics at rupture sites of middle cerebral artery aneurysms: a CFD study with intraoperative correlation

Objective To characterise the hemodynamic environment at the intraoperatively confirmed rupture point, relative to the aneurysm sac and parent artery, in middle cerebral artery aneurysms (MCAAs), using CT angiography (CTA)-based computational fluid dynamics (CFD). Materials and methods Preoperative CTA data from 15 patients with ruptured MCAAs were reconstructed in three dimensions. Transient CFD simulations were run under rigid-wall and Newtonian-fluid assumptions to compute time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), pressure, and flow streamlines. Rupture regions were identified intraoperatively. No daughter sac, bleb, or secondary lobulation was identified on the preoperative CTA reconstructions or at surgery. Parameters were compared across the three locations using the Friedman test and pairwise Wilcoxon signed-rank tests with Bonferroni correction ( p < 0.0167). Results TAWSS decreased monotonically from the parent artery (median 9.97 Pa) to the aneurysm sac (4.58 Pa) and then to the rupture point (2.14 Pa; all pairwise p ≤ 0.003). OSI was higher at the rupture point than at the aneurysm sac and parent artery ( p = 0.0003 and 0.0002), with no difference between the latter two ( p = 0.252). Pressure was higher at the rupture point and the aneurysm sac than at the parent artery ( p = 0.005 and 0.009) but did not differ between the first two ( p = 0.027). Friedman tests were significant for all three parameters (TAWSS: p < 0.0001; OSI: p = 0.0004; pressure: p = 0.0011). The rupture region coincided spatially with the low-TAWSS and high-OSI areas of the sac: rupture-point TAWSS was lower than sac TAWSS in 14 of 15 patients, and rupture-point OSI exceeded sac OSI in 13 of 15. Conclusion CTA-based CFD resolved region-level differences in TAWSS and OSI between the rupture region, the aneurysm sac, and the parent artery. TAWSS and OSI, but not pressure, differed between the rupture point and the aneurysm sac, indicating that low TAWSS and high OSI rather than elevated pressure characterize the rupture point.