The research on postoperative collateral formation for hemorrhagic moyamoya disease (MMD) evaluated by using digital subtraction angiography (DSA) is limited. Our study objective was to investigate the postoperative collateral formation after indirect bypass for hemorrhagic MMD. Methods: All consecutive inpatients with hemorrhagic MMD who received indirect bypass at Beijing Tiantan screened. The site of the hemorrhage was classified as either anterior or posterior. Postoperative collateral

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... tion was evaluated on lateral views using the Matsushima scale. Univariate and multivariate logistic regression analyses were carried out to determine the factors influencing postoperative collateral formation. Results: Six-four patients (64 hemispheres) were included in this study. After a median 8.5 months DSA follow-up, 14 (21.9%) hemispheres had grade A collateral circulation, 13 (20.3%) had grade B, and 37 (57.8%) had grade C. Twenty-seven (43.2%) hemispheres had good postoperative collateral formation and 37 (57.8%) had poor postoperative collateral formation. The univariate logistic regression analyses showed that age at operation (OR, 0.954; 95% CI, 0.908-1.003; p=0.066), hemorrhagic site (OR, 4.694; 95% CI, 1.582-13.923; p=0.005), and PCA involvement (OR, 3.474; 95% CI, 0.922-13.086; p=0.066) may effect postoperative collateral formation. The multivariate logistic regression analyses showed that only anterior hemorrhage (OR, 5.222; 95% CI, 1.605-16.987; p=0.006) was significantly related to good postoperative collateral formation. Conclusion: Anterior hemorrhage was significantly related to good postoperative collateral formation after indirect bypass.