Primary Gamma Knife Radiosurgery for Trigeminal Schwannoma: A Retrospective Analysis of Long-Term Functional Outcomes.

INTRODUCTION: Trigeminal schwannomas (TSs) are rare benign tumors arising from the trigeminal nerve. Gamma Knife radiosurgery (GKS) offers a minimally invasive alternative to surgical resection, but the long-term clinical outcomes, particularly regarding change of trigeminal nerve function, remain under-characterized. This study aimed to evaluate long-term clinical outcomes and identify prognostic factors for neurological sequelae following primary GKS for TS. METHODS: A retrospective analysis was performed on 89 patients who underwent primary GKS for TS between 2002 and 2023. Patients with prior surgery or hypofractionation were excluded. Clinical and imaging data were analyzed for tumor control, symptom relief, and new-onset, or persistent post-GKS morbidities. Symptoms were classified as new-onset transient, new-onset permanent, or persistent preexisting. The Kaplan-Meier analysis, Logistic regression, and Cox regression were used to identify prognostic factors. RESULTS: Over a median follow-up of 57 months (range, 6.8-184), tumor control was 93.3%. Symptom relief occurred in 46.9% of preexisting deficits, highest for headache (70.6%) and dizziness (100%), but modest for trigeminal pain (33.3%) and paresthesia (36.7%). New-onset morbidities included trigeminal sensory disturbance (33.7%, permanent in 15) and pain (22.5%, permanent in 5). In Cox analysis, higher margin dose reduced the hazard of new paresthesia (HR 0.511, p = 0.036), while older age increased risk (HR 1.041, p = 0.037). CONCLUSION: Primary GKS achieves durable tumor control for TS with lower risk than microsurgery. However, a considerable proportion of patients may experience long-term trigeminal dysfunction. Adequate dosing may mitigate sensory morbidity, though pain relief remains modest. Careful selection, counseling, and follow-up are essential.