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To evaluate the predictors of remnant tumor regrowth and need for salvage therapy after less than gross total resection (GTR) of vestibular schwannoma (VS).Retrospective chart review.Tertiary neurotologic referral center.Patients who underwent VS resection between 2008 and 2019 either with GTR, near total resection (NTR), and subtotal resection (STR).Microsurgical resection, salvage radiosurgery.Regrowth free interval, salvage free interval, tumor doubling rate.Three hundred eighty five cases (GTR = 236, NTR = 77, and STR = 71) from 2008 to 2019 were included. STR cohort had much larger and complex tumors with significant differences in tumor volume, ventral extension and brainstem compression (p 0.001). On single predictor analysis, tumor volume, ventral extension, brainstem compression as well as STR strategy was associated with significant increased risk of regrowth and need for salvage therapy. Multivariate analysis revealed STR strategy as significant predictor of regrowth (hazard ratio 3.79, p 0.0005). Absolute remnant volume and extent of resection (EOR) did not predict regrowth. A small proportion of cases (NTR = 4%, STR = 15%) eventually needed salvage radiosurgery with excellent ultimate local tumor control with no known recurrence to date.Conservative surgical strategy employing NTR or STR can be employed safely in large and complex VS. While there is increased risk of regrowth in the STR cohort, excellent local control can be achieved with appropriate use of salvage radiosurgery. No disceret radiologic or operative predictors of regrowth were identified.

Radiation-associated malignancy and malignant transformation are risks associated with stereotactic radiosurgery (SRS); however, incidence is uncertain. The purpose of our study is to present the rate of radiation-associated malignancy and malignant transformation at our institution. After IRB approval, we undertook a retrospective cohort study evaluating patients treated with Gamma Knife® or linac-based SRS between 1990 and 2014 for benign CNS pathology with at least 5 years of clinical follow-up. Risk of transformation was calculated using the Kaplan-Meier method. A total of 273 patients met selection criteria. Median clinical follow-up after SRS was 11 years (range 5-27). Over 3,216 patient-years following SRS, we found zero cases of radiation-associated malignancy and two cases of radiation-associated malignant transformation for a crude rate of 0.73% or case rate of 0.62 per 1,000 patient-years. The Kaplan-Meier risk of malignant transformation at 5, 10, and 15 years was 0.4% (95% CI 0.05% 2.6%). These data support the continued use of SRS for benign intracranial pathology without significant concern for secondary malignancy.