Lamina Terminalis and Membrane of Liliequist Fenestration with Basal Cisternostomy: Permanent Cerebrospinal Fluid Diversion Rates in Aneurysmal Subarachnoid Hemorrhage in a Single-Center Retrospective Cohort Study

BACKGROUND: Shunt-dependent hydrocephalus (ShDH) remains a source of morbidity after aneurysmal subarachnoid hemorrhage (aSAH). During microsurgical clipping, lamina terminalis (LT) fenestration with basal cisternostomy (BC) and membrane of Liliequist (MoL) fenestration (LTF-BC) can potentially reduce shunt dependency. OBJECTIVE: To evaluate permanent cerebrospinal fluid (CSF) diversion rates and clinical outcomes in patients with aSAH undergoing microsurgical aneurysm occlusion with LTF-BC and MoL fenestration, and to identify factors associated with them. MATERIALS AND METHODS: We performed a single-center retrospective cohort study using an institutional registry (2014-2023). Of 381 patients screened, 331 with ruptured aneurysms treated microsurgically with LTF-BC and MoL fenestration were included. Primary outcomes were permanent CSF diversion and 3-year functional outcome (modified Rankin Scale [mRS]). Multivariable logistic regression and Firth regression were performed. An external comparator analysis provided descriptive absolute risk reduction (ARR) and number needed to treat (NNT) estimates. RESULTS: Median age was 55 years; 56.8% were women, 81.3% had Fisher grade III-IV hemorrhage, and 39.6% had acute hydrocephalus. Temporary CSF diversion was required in 50/131 (38.2%) patients with acute hydrocephalus. At 3 years, mRS was available for 326/331 patients; 244/326 (74.8%) had a good outcome (mRS 0-3). Permanent CSF diversion was performed in 9/331 patients (2.7%). Temporary CSF diversion was the only independent predictor of 3-year shunt dependency (odds ratio (OR) 5.08, 95% confidence interval (CI) 1.12-23.18; P = 0.036). Independent predictors of worse 3-year functional outcome were increasing age (OR 0.96 per year, 95% CI 0.94-0.99; P = 0.003), World Federation of Neurosurgical Societies grade ≥3 (OR 0.34, 95% CI 0.19-0.62; P < 0.001), and intraventricular hemorrhage (OR 0.42, 95% CI 0.23-0.75; P = 0.004). In external comparison, permanent CSF diversion was lower than in the nonfenestration cohort (2.7% vs 17.9%; ARR 15.2%; NNT 6.59). CONCLUSION: LTF-BC with MoL fenestration was associated with a low 3-year permanent CSF diversion rate despite high hemorrhage severity. Temporary CSF diversion identified a subgroup at increased risk for future shunt dependency.