Gamma knife radiosurgery for trigeminal schwannoma: a 20-year experience with long-term treatment outcome

This study evaluated the long-term tumor control rate (TCR) and symptomatic outcomes of patients treated with gamma knife radiosurgery (GKRS) for trigeminal schwannomas (TSs). Thirty-two patients with TS who underwent GKRS between January 1994 and January 2013 with at least 2 years of follow-up were enrolled in the study. Clinical charts and surgical records were retrospectively reviewed to evaluate factors affecting TCR and symptomatic outcomes. The median patient age was 57.5 years (max = 81, interquartile range [IQR] = 51-67), and the median tumor volume was 3.55 cm(3) (max = 25.2 cm(3), IQR = 2.0-6.2 cm(3)). The median marginal and maximum doses were 13.0 Gy (max = 18.0 Gy, IQR = 12.5-15 Gy) and 23.8 Gy (max = 35 Gy, IQR = 21.7-25.0 Gy), respectively. At a median follow-up of 90.5 months (max = 281 months, IQR = 49-139.75 months), the actuarial 3-, 5-, and 10-year TCR were 93.8, 86.2, and 80.8%, respectively. Our data and multivariate analysis indicated that the target volume was the only significant factor determining TCR and that larger tumors (> 5 cm(3)) were more likely to progress (p = 0.011). Cystic tumors had a higher incidence of transient enlargement and temporary symptom change compared to those in solid tumors. An unfavorable outcome of symptoms was observed in five patients (15.6%). Complications were observed in two patients (6.25%), including hydrocephalus and radio-induced trigeminal neuropathy, respectively. GKRS can be a safe and effective treatment modality for TS with long-term follow-up, especially for small tumors. An extended period of follow-up observation is required to conclude the clinical response to GKRS.