Side-to-Side versus Traditional End-to-Side Approach to STA-MCA Bypass in Moyamoya Disease: A Comparative Meta-Analysis

Background Superficial temporal artery to middle cerebral artery (STA-MCA) bypass is a standard-of-care treatment for adult patients with moyamoya disease (MMD). Although the classical technique is end-to-side (E-S) bypass, the side-to-side (S-S) construct has emerged as an alternative strategy with potentially reduced risk of postoperative cerebral hyperperfusion syndrome (CHS). Methods A PRISMA-compliant systematic review of MEDLINE and Embase databases was performed from inception to May 2026 identifying 72 studies. After abstract screening, 14 studies underwent full-text review, and five head-to-head studies met inclusion criteria. A meta-analysis and supplemental sensitivity analyses were conducted to assess robustness, excluding a high-variance study with disparate CHS diagnostic thresholds. Results Five studies were included capturing head-to-head outcomes for a total of 495 patients (194 E-S; 301 S-S). Pooled analysis showed no significant difference in CHS incidence with S-S bypass compared to E-S bypass. Sensitivity analysis excluding a study with high CHS incidence revealed a significant reduction of CHS with S-S bypass (OR=1.63,95%CI=1.19–2.25, p=0.016), possibly due to decreased heterogeneity, or their including of high-sensitivity diagnostic tools including LSCI and SPECT, which may have identified a higher incidence of subclinical CHS. No significant difference was observed in the reported incidence of stroke in either model. Findings were unchanged when the analysis was limited to the non-overlapping cohorts. Conclusion S-S constructs for STA-MCA in adult MMD may reduce CHS risk, but without an associated difference in risk of postoperative stroke. Future studies with standardized reporting of CHS are required to validate S-S bypass as a preferred strategy.