Gamma knife radiosurgery for trigeminal neuralgia: results and potentially predictive parameters--part I: idiopathic trigeminal neuralgia

OBJECTIVE: Gamma knife radiosurgery (GKR) is an increasingly used, minimally invasive treatment option for patients with trigeminal neuralgia (TN) refractory to medical therapy. This retrospective study evaluates the long-term results and side effects of GKR in the treatment of TN focusing on potentially predictive factors. METHODS: One hundred sixty patients with TN were included in this study (minimum follow-up, >6 mo; mean, 37.4 mo; range, 6-144 mo). In 92 patients, GKR represented the first nonmedical option ("primary GKR"). In 68 patients, invasive treatments had been previously attempted. All patients were treated using a single 4-mm collimator shot targeting the pontine trigeminal root entry zone with a maximal dose of 75 to 95 Gy. Brainstem dose exposure never exceeded 15 Gy. Treatment outcome results were classified as Grade I (pain-free with no pharmacological treatment), Grade II (pain-free with pharmacological treatment), and Grade III (no result). Data were analyzed using the log-rank test for univariate analysis and the ordered logit model for multivariate analysis. RESULTS: In the overall series, 98 (61\%) out of 160 patients reached a Grade I outcome, 45 (29\%) reached a Grade II outcome, and 17 (10\%) patients had no results from GKR. These results were encouraging for patients with typical facial pain features and for patients treated by a "primary" gamma knife. Considering the global outcome, the most effective and safest dose was found to be in the 80 to 90 Gy range. CONCLUSION: According to our experience, GKR represents a reliable second-line therapeutic approach for TN after pharmacological failure. Favorable prognostic factors include "primary GKR" and maximal GKR dose ranging between 80 and 90 Gy.