or elevated after a certain period.In cases that develop hydrocephalus weeks or months after SAH, shunt surgery is indicated.The incidence of shunt-dependent hydrocephalus in SAH patients has been reported to range from 6 to 37% (21).Several studies have reported on those factors related to the development of shunt-dependent hydrocephalus following SAH (8,10,21-24,26).Although there are some differences in the reported risk factors, several factors have been commonly recognized as significant including advanced age, acute █ INTRODUCTION H ydrocephalus, a well-known complication of aneurysmal subarachnoid hemorrhage (SAH), generally has been divided into three stages: acute (0-3 days after SAH), subacute (4-13 days after SAH), and chronic (≥ 14 days after SAH) (25).Hydrocephalus occurring during the acute or subacute stage is commonly treated with an external ventricular drain (EVD) and a shunt procedure is performed if hydrocephalus develops when the drainage bag is clamped AIM: Surgical procedures for aneurysmal subarachnoid hemorrhage (SAH) are increasing among the elderly as the population ages.Chronic shunt-dependent hydrocephalus is a recognized complication of SAH.The aim of this study was to identify predictive factors for the development of shunt-dependent hydrocephalus among elderly patients with SAH. MATERIAL and METHODS:We retrospectively studied 878 patients, including 275 patients ≥ 65 years old, with SAH treated between 2005 and 2015 to identify factors contributing to the development of shunt-dependent hydrocephalus.The relationships between shunt-dependent hydrocephalus and the causative factors were analyzed using univariate and multivariate analysis; the causative factors were based on the results of previous studies. RESULTS:In the 878 patients with SAH, there was a significant difference in the incidence of shunt-dependent hydrocephalus between patients < 65 years old and those ≥ 65 years old (p=0.021).In the 275 patients ≥ 65 years old, the following were associated with shunt-dependent hydrocephalus on univariate analysis: 1) Hunt and Hess grade (p=0.005), 2) Fisher grade (p<0.001), 3) intraventricular hemorrhage (p<0.001),4) acute hydrocephalus (p=0.003), 5) aneurysm location (p=0.001), and 6) external ventricular drain placement (p<0.001).On multivariate analysis, only 1) intraventricular hemorrhage (p<0.001) and 2) a ruptured aneurysm located in the distal posterior circulation (p=0.014) were related to an increased risk for the development of shunt-dependent hydrocephalus.CONCLUSION: Evaluating risk factors can help identify patients at high risk of developing shunt-dependent hydrocephalus.Identifying these risk factors may help neurosurgeons to provide optimal therapy and improve outcomes in patients with SAH.