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Introduction Neointimal hyperplasia resulting in in-stent stenosis is a well-documented complication associated with flow diverter (FD) implantation for intracranial aneurysms. Recent research underscores the importance of identifying risk factors and understanding the progression of this condition, which is essential for informed clinical surveillance and management strategies. The primary aim of this systematic review and meta-analysis was to thoroughly assess the predictors of severe in-stent stenosis and the progression patterns following flow diversion treatment for intracranial aneurysms.Methods A comprehensive search was performed across PubMed, MEDLINE, and Embase databases in accordance with PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) to identify studies reporting on neointimal hyperplasia, in-stent stenosis rates, risk factors, and progression following flow diverter implantation for intracranial aneurysms. Demographic data and imaging findings, including aneurysm characteristics, percentage of stenosis, locations, and follow-up imaging, were analyzed. The severity of in-stent stenosis was designated as the primary outcome. .Results 18 studies with 758 patients have been included in the study. The stenosis has been classified into 4 categories based on the percentage of stenosis as<25%,25-50%,50-75% and >75%. Moderately severe or severe stenosis (>50%) was considered significant for analysis.Female sex(p<0.05), Hypertension(p<0.001), Hyperlipidemia(p<0.001), smoking(p<0.001) was associated with greater risk of severity of stenosis. The usage of adjunctive coiling and balloon angioplasty(p<0.05) were associated with severe in stent stenosis. Only 6% of patients with stent stenosis were symptomatic. Follow up imaging was available in eleven studies. The mean follow up period was 14.32 months. The aneurysm location in ophthalmic, cavernous ICA (p<0.00006), usage of Silk devices instead of Pipeline device (p<0.0012),symptomatic stenosis(p<0.05), higher degree of stenosis(p<0.00190), the usage of coiling(p<0.02) and usage of SAPT(P<0.012) were associated with progression of in stent stenosis.Conclusion This systematic review identifies that the progression and severity of in-stent stenosis following flow diverter treatment for intracranial aneurysm are influenced by several nonmodifiable factors (such as sex) and modifiable patient factors (including hypertension, hyperlipidemia, and smoking), as well as intervention techniques, such as device selection and procedural methods. These findings underscore the need for tailored management and long-term surveillance to improve the outcome in patients.Disclosures K. Arumalla: None. B. Tong: None. A. Sonig: None.Abstract E-183 Figure 1