Journal of Neurosurgery 2026;145(3):743-754
Follow-up after stereotactic radiosurgery for vestibular schwannoma must assess more than tumor control: ventricular enlargement can introduce a separate clinical problem, even without overt obstruction. Bauman and colleagues combine an adult institutional cohort with a systematic review to examine this complication and distinguish radiological change from symptomatic hydrocephalus requiring cerebrospinal fluid diversion. Their findings identify associations with age, target volume and subsequent tumor growth, while showing that some patients with enlarged ventricles remain asymptomatic. The central clinical message is therefore one of informed surveillance and individualized assessment, rather than automatic shunting based on imaging alone.
Objective
To determine the incidence and associated risk factors of nonobstructive ventricular enlargement and symptomatic communicating hydrocephalus following primary stereotactic radiosurgery (SRS) for vestibular schwannoma.
Methods
The retrospective Mayo Clinic cohort included 634 patients treated with primary Gamma Knife radiosurgery between January 2000 and July 2023. Median age was 64 years, with a range of 18-89 years. Exclusions included previous tumor resection, preexisting shunts or relevant hydrocephalus, post-SRS obstructive hydrocephalus and follow-up shorter than six months. Median imaging follow-up was 61 months.
The investigators separately examined nonobstructive ventricular enlargement and symptomatic hydrocephalus requiring ventriculoperitoneal shunting. Logistic regression assessed associated factors. Tumor change was classified using the latest available imaging relative to treatment imaging, with salvage-treated progression categorized as growth.
A systematic review searched three databases through January 2024. Twenty-nine studies, including the institutional cohort, contributed 7,825 patients to a random-effects meta-analysis. The institutional adult data and the pooled literature estimates should be distinguished rather than treated as a single homogeneous population.
Main results
Ventricular enlargement occurred in 23/634 patients (3.6%); nine remained asymptomatic and 14 (2.2% of the cohort) required shunting, at a median of eight months after SRS. Age ≥65 years, target volume ≥5 cm³ and subsequent tumor growth were associated with shunt-requiring hydrocephalus in adjusted analyses. The literature synthesis estimated ventricular enlargement/hydrocephalus at 5% and shunt-requiring disease at 4%, with substantial heterogeneity. The study did not reliably distinguish which patients with established ventricular enlargement would subsequently need a shunt.
Interpretation – operative relevance
The findings support closer clinical attention to higher-risk patients and assessment of ventricular change alongside tumor response. Radiological enlargement alone did not mandate diversion in this cohort. The 5 cm³ threshold is an exploratory risk discriminator, not a validated contraindication to SRS or an indication for prophylactic shunting. Likewise, the association with maximum radiation dose concerned ventricular enlargement, not demonstrated shunt dependence; it does not establish that changing dose prevents symptomatic hydrocephalus. Decisions about diversion remain clinical rather than threshold-driven.
Limitations
The institutional analysis was retrospective and included only 23 ventricular-enlargement events and 14 shunt procedures. Multivariable estimates consequently have substantial uncertainty. Treatment-selection patterns favored SRS for smaller lesions, limiting generalizability to the full vestibular schwannoma population. Shunt indications were not governed by uniform, prospectively specified criteria.
Tumor growth was assessed at the latest follow-up, so its association with hydrocephalus should not be interpreted as a validated baseline predictor or proof of temporal causation. The proposed protein-mediated impairment of CSF absorption remains a hypothesis; occult partial obstruction is an alternative discussed by the authors.
The literature synthesis combined heterogeneous definitions, treatment populations and follow-up practices. Statistical heterogeneity was high for both pooled incidence estimates. Some eligible series mixed primary and secondary SRS, and the pooled results were not presented as an adult-only subgroup. The pooled shunting proportion among patients with ventricular enlargement should not be applied as an individual probability or substituted for clinical assessment.
Clinical takeaway
After vestibular schwannoma radiosurgery, evaluate ventricular changes in their clinical context, particularly in older patients, larger treated tumors and cases with subsequent growth. This study supports vigilance but provides neither a reliable rule for predicting shunt dependence nor evidence for prophylactic CSF diversion.