Abstract Body: Introduction
Extracranial-intracranial (EC-IC) bypass has evolved in recent years with more focus on indications, selection criteria, surgical methods, and postop management. Recent studies observed decreased utilization of EC-IC bypass and increased complications leading up to year 2015. In this study, we aim to study trends in EC-IC bypass throughout the years.

Methods
Using the National Inpatient Sample 2016-2019, hospital admissions with carotid occlusive disease (COD), moyamoya, subarachnoid hemorrhage (SAH), unruptured intracranial aneurysm (UIA) were identified using ICD-10 diagnosis codes. Trends in ECIC-Bypass utilization, demographic and hospital characteristics, and unfavorable outcome were evaluated for each condition.

Results
From 2016 to 2019, total number of EC-IC procedures increased significantly by 43% from 740 to 1060 weighted cases. Year after year, an increasing number of procedures were performed in urban teaching hospitals compared to rural or non-teaching hospitals for all indications. The most common indication was moyamoya, accounting for 58.1% in 2016, increasing to 60.8% in 2019. COD was the next common indication, comprising 26.4% in 2016, but slightly decreasing to 25.9% in 2019. Similarly, UIA accounted for 10.8% in 2016, declining to 8.5% in 2019. SAH remained stable at 4.7% in both 2016 and 2019 (Figure 1). Percentage of unfavorable outcome, including death, slightly increased for procedures in moyamoya and SAH cases and slightly decreased for COD and UIA.

Conclusion
Overall number of EC-IC procedures increased significantly from 2016 to 2019. Urban teaching hospitals performed the increasing majority. Moyamoya was the primary indication for more than half of the procedures, exhibiting an increasing trend over the study period. While SAH did not show any significant changes, the percentage of procedures for COD and UIA decreased. The prevalence of unfavorable outcomes varied among different indications.