Predicting late-onset hydrocephalus in pediatric medulloblastoma: from static anatomy to dynamic biological assessment.

Postoperative disturbances in cerebrospinal fluid (CSF) dynamics remain a major complication after pediatric medulloblastoma (MB) resection and may necessitate permanent ventriculoperitoneal shunting (VPS). Existing risk assessment tools have important methodological limitations: many are derived from heterogeneous posterior fossa tumor cohorts and rely predominantly on static preoperative anatomical variables, with limited consideration of tumor-specific invasion patterns or postoperative biological factors. To identify multidimensional factors associated with delayed postoperative ventriculoperitoneal shunt (VPS) requirement after pediatric medulloblastoma resection and to explore how preoperative, pathological, molecular, and postoperative features contribute to modeled risk patterns. We retrospectively analyzed 269 pediatric patients with medulloblastoma who underwent tumor resection between January 2019 and January 2024. The primary endpoint was delayed postoperative hydrocephalus requiring VPS more than 2 weeks after tumor resection for persistent intracranial hypertension and progressive ventricular enlargement. Firth penalized logistic regression was designated as the primary association model. Model performance was assessed using C-statistics, calibration curves, decision curve analysis, and internal bootstrap validation. A multi-algorithm AUC heatmap and ElasticNet-based SHAP analysis were used as secondary exploratory analyses, and the nomogram was derived from the Firth model. Among 269 children treated between 2019 and 2024, 18 (6.7%) developed delayed postoperative hydrocephalus requiring VPS more than 2 weeks after resection. In the primary Firth model, postoperative hemorrhage (OR 22.40, 95% CI 4.24-118.0, P < 0.001) and choroid plexus invasion (OR 18.00, 95% CI 3.34-96.9, P < 0.001) showed the strongest positive associations, although the wide confidence intervals indicate substantial uncertainty. Auxiliary SHAP analysis identified postoperative hemorrhage and age as prominent global contributors, while choroid plexus invasion showed large contributions in positive cases and Group 3 and Group 4 displayed contrasting higher- and lower-risk patterns. The findings support a multi-hit pattern in which limited baseline CSF compensatory reserve may be followed by postoperative hemorrhagic or inflammatory insults. The proposed model is exploratory and is not yet ready for individual clinical decision-making. Its performance and feature-contribution patterns should be tested in prospectively enrolled multicenter cohorts using prespecified variables and the same endpoint.