Objectives: Intraoperative aneurysm rupture (IOAR) is a common complication during intracranial aneurysm(s) (IA) surgery. In virtue of paradigm shift regarding IA selected for clipping in the post-ISAT era, we aimed to evaluate the risk factors and impact of IOAR in an institutional series of clipped ruptured (RIA) and unruptured (UIA) IA.

Material and Methods: All IA treated by microsurgical clipping at our institution between 2003 and 2016, were eligible for this study. Demographic, clinical and radiographic factors were correlated with occurrence of IOAR in univariate and multivariate analyses. Impact on outcome was analyzed for RIA and UIA separately.

Results: 903 clipped IAs were included in the final analysis (538 UIA and 365 RIA). IOAR occurred in 163 cases (18.1%), mostly during clipping of RIA (37.5% vs. 4.8%) In multivariate analysis, ruptured status (adjusted odds ratio [aOR] =10.46; p<0.001), sack size (aOR=1.05 per-mm-increase, p=0.038) and IA location in the anterior communicating artery (aOR=2.31, p<0.001) independently predicted IOAR. For RIA cases, IOAR was also independently predicted by rebleeding before therapy (aOR=3.11, p=0.033) and clinical severity of subarachnoid hemorrhage (aOR=1.18 per-WFNSgrade-
increase, p=0.049). IOAR independently predicted poor outcome (aOR=1.83,
p=0.042) after RIA surgery. In turn, IOAR impacted only the risk for cerebral infarct(s) (OR=3.75, p=0.003) and incomplete IA occlusion (OR=3.45; p=0.003) for UIA cases, but not the outcome (p=0.263).

Conclusion: IOAR was independently predicted by the ruptured status, location and size of IA, as well as by initial severity of aneurysmal bleeding and pretreatment rebleeding. Impact of IOAR differed between RIA and UIA cases.