Direct, Indirect, and Combined Extracranial-to-Intracranial Bypass for Adult Moyamoya Disease: An Updated Systematic Review and Meta-Analysis

Background: Moyamoya disease is a chronic, progressive cerebrovascular disease involving occlusion or stenosis of the terminal portion of the internal carotid artery. We conducted an updated systematic review and meta-analysis to investigate clinical and angiographic outcomes comparing direct, combined, and indirect bypass for the treatment of moyamoya disease in adults. Methods: Two independent authors performed Preferred Reporting Items for Systematic reviews and Meta-Analyses guided literature searches in December 2021 to identify articles reporting clinical/angiographic outcomes in adult moyamoya disease patients undergoing bypass. Primary end points used were ischemic and hemorrhagic strokes, clinical outcomes, and angiographic revascularization. Study quality was evaluated with Newcastle-Ottawa and the Oxford Center for Evidence-Based Medicine scales. Results: Four thousand four hundred fifty seven articles were identified in the initial search; 143 articles were analyzed. There were 3827 direct, 3826 indirect, and 3801 combined bypasses. Average length of follow-up was 3.59±2.93 years. Pooled analysis significantly favored direct (odds ratio [OR], 0.62 [0.48–0.79]; P P P P =0.0001) and combined (OR, 0.53 [0.41–0.69]; P P P P =0.0001) over indirect bypass for early stroke, late stroke, late intracerebral hemorrhage, and favorable outcomes, respectively. Indirect bypass was favored over combined (OR, 3.1 [1.7–5.6]; P P P P =0.002) and combined (OR, 0.23 [0.12–0.43]; P P P =0.01). Conclusions: Based on combined meta-analysis (43 articles) and pooled analysis (143 articles), the existing literature indicates that combined and direct bypasses have significant benefits for patients suffering from late stroke and hemorrhage versus indirect bypass. Combined bypass was favored over indirect bypass for favorable outcomes. This is a strong recommendation based on low-quality evidence when utilizing the Grades of Recommendation, Assessment, Development, and Evaluation system. These findings have important implications for bypass strategy selection.