Radiosurgical Decompression of Trigeminal Nerve and Its Correlation with Functional Outcome in Tumor-Related Trigeminal Neuralgia

BACKGROUND: Target selection during Gamma Knife radiosurgery (GKRS) in cases of tumor-related trigeminal neuralgia is always debatable. We analyzed the correlation of regression of tumor size and degree of release of the nerve with long-term pain control. METHODS: Between March 2012 and March 2023, 50 cases of tumor-related trigeminal neuralgia were treated with GKRS (tumor was targeted). Radiological findings after GKRS were categorized into 3 types: 1) tumor volume remained same or decreased, additional segment of nerve not seen; 2) tumor volume decreased, additional segment of trigeminal nerve seen, but tumor still adherent to the nerve; 3) tumor volume decreased, adjacent nerve seen completely separated from tumor. Pain score before and after GKRS (Barrow Neurological Institute I - III: good; Barrow Neurological Institute IV and V: poor) was correlated with these subgroups. RESULTS: At median follow-up of 46.5 months, 18 cases showed type 1 radiological response, 23 showed type 2 response, and 9 showed type 3 response. Good pain control was achieved in 10 (55.5%) patients with type 1,15 (65.21%) with type 2, and 7 (77.8%) with type 3 responses. The outcome differences among these 3 groups were not statistically significant ( P = 0.519). Five patients with type 3 radiological response were off medication, which was statistically better than type 1 and type 2 radiological responses, with 3 patients ( P = 0.012) and 2 patients ( P = 0.002), respectively, still receiving medication. CONCLUSIONS: Tumor volume reduction after GKRS may associated with good pain control in tumor-related trigeminal neuralgia. Further, this allows visualization of additional segment of nerve that can be targeted in a second session for treating recurrent or failed cases.