Inflammation Meets Ventricular Dynamics: Combined Hematologic and Radiologic Predictors of Shunt-Dependent Hydrocephalus in Endovascularly Treated Patients with Aneurysmal Subarachnoid Hemorrhage

Background/Objectives: Shunt-dependent hydrocephalus remains a major complication following aneurysmal subarachnoid hemorrhage (aSAH). Although several clinical–radiological prediction models have been proposed, the additional contribution of inflammatory biomarkers remains unclear. This study evaluated whether the platelet-to-neutrophil ratio provides additional predictive value beyond established clinical and radiological predictors of shunt-dependent hydrocephalus after aSAH. Materials and Methods: This retrospective single-center cohort study included 418 consecutive patients with aSAH treated using endovascular techniques between 2017 and 2025. Clinical severity parameters, ventricular burden-related radiological findings, and admission hematological variables were analyzed. Independent predictors of shunt-dependent hydrocephalus were identified using multivariable logistic regression analysis. Model performance was assessed using receiver operating characteristic analysis, calibration assessment, sensitivity analyses, and bootstrap internal validation. Results: Shunt-dependent hydrocephalus developed in 75 patients (18%). Lower Glasgow Coma Scale scores, intraventricular hemorrhage, increased Evans index, greater third ventricle width, lower platelet-to-neutrophil ratio, and external ventricular drain requirement were independently associated with shunt dependency. Incorporation of the platelet-to-neutrophil ratio increased the area under the curve from 0.84 (95% CI: 0.79–0.89) to 0.88 (95% CI: 0.84–0.92; p = 0.018). Internal validation demonstrated preserved model performance and calibration. Sensitivity analyses demonstrated similar findings after exclusion of external ventricular drain placement. Conclusions: Platelet-to-neutrophil ratio is independently associated with shunt-dependent hydrocephalus after aSAH and may be considered an additional component of integrated clinical–radiological risk assessment.