High-flow Extracranial-to-Intracranial Bypass for Complex and Giant Cerebral Aneurysms: A Systematic Review and Meta-Analysis

Background Intracranial aneurysms affect 3–5% of adults, with giant aneurysms posing substantial therapeutic challenges for which high-flow extracranial-to-intracranial (HF EC-IC) revascularization may be required. Methods A systematic literature search of PubMed, Embase, the Cochrane Library, and ClinicalTrials.gov was performed following PRISMA guidelines up to July 2025 to identify randomized controlled trials (RCTs), cohort, observational studies about HF EC-IC bypass for complex and giant cerebral aneurysms. Meta-analysis was performed using Review Manager (RevMan 5.4.1) with a random-effects model. Results Across 13 studies, patients receiving the intervention three times more likely to achieve favorable functional outcome compared to controls (pooled OR 3.09; 95% CI: 1.91–5.00). The effect was significant (Z = 4.59, p < 0.00001) despite high heterogeneity (I² = 83%, Chi² = 68.69, p < 0.00001), likely due to variability in surgical techniques, patient characteristics, aneurysm complexity, and follow-up durations. Nonetheless, most studies reported ORs above 1.0, suggesting a consistent benefit of the intervention in improving functional outcomes. Among 11 studies, the intervention was associated with over tenfold higher odds of maintaining graft patency (pooled OR 10.56; 95% CI: 5.98–18.64), statistically significant (Z = 8.13, p < 0.00001) with moderate heterogeneity (I² = 56%) attributable to patient populations, surgical techniques, graft types, and follow-up durations. Despite several studies reported high OR with wide confidence intervals, overall evidence demonstrates the intervention markedly improves graft patency. Conclusions HF EC-IC revascularization demonstrates consistent functional benefits and substantially enhances graft patency in complex and giant intracranial aneurysms, supporting its role in challenging cerebrovascular cases