Endoscopic third ventriculostomy for idiopathic normal pressure hydrocephalus: association of cerebrospinal fluid flow dynamics with outcome.

Introduction: Endoscopic third ventriculostomy (ETV) has been proposed for selected patients with idiopathic normal pressure hydrocephalus (iNPH), but predictors of sustained benefit are uncertain. Phase-contrast MRI (PC-MRI) may quantify cerebrospinal fluid (CSF) pulsatility and support patient selection. Research question: Is sustained clinical improvement after primary ETV associated with preoperative aqueductal CSF flow parameters measured by PC-MRI? Material and methods: In this prospective single-centre observational study, patients with iNPH underwent primary ETV after standardized diagnostic work-up. Preoperative assessment included the Kiefer scale and PC-MRI measurements at the cerebral aqueduct: peak velocity (PV), aqueductal stroke volume (ASV), and net ASV. Clinical follow-up was performed for 12 months. Sustained response was defined as an NPH recovery rate ≥3 at 3 and 12 months without secondary ventriculoperitoneal shunt implantation. Analyses were exploratory. Results: Thirty-one patients were included, of whom 10 (32.3%) achieved sustained clinical improvement. Responders demonstrated significantly higher preoperative ASV values compared to non-responders. Among the evaluated parameters, ASV was the only variable significantly associated with clinical response. Receiver operating characteristic (ROC) analysis demonstrated good discriminatory capacity for ASV (area under the curve [AUC] 0.83). An exploratory cut-off value of 280 μl yielded a sensitivity of 90%, specificity of 71%, positive predictive value of 60%, and negative predictive value of 94%. Discussion and conclusion: Higher preoperative ASV was associated with sustained clinical improvement after primary ETV in this small iNPH cohort. PC-MRI-derived ASV may help identify candidates unlikely to benefit from ETV, but the proposed threshold requires external validation before clinical use.