Purpose Stereotactic radiosurgery (SRS) provides a noninvasive treatment modality to patients with medically refractory trigeminal neuralgia. The root entry zone (REZ) has been proposed to be an ideal stereotactic target due to its partial makeup of centrally produced myelin, conferring a theoretical increased sensitivity to irradiation, as well as increased susceptibility to neurovascular conflict, making it the site in which nociceptive signals likely arise. The aim of this study is to determine if there is a statistically and clinically significant difference in pain relief or facial hypesthesia following SRS based on distance of the stereotactic isocenter from REZ. Methods Patients undergoing Novalis radiosurgery for the treatment of trigeminal neuralgia with at least three months follow-up were included in this study. Post-operative outcomes were stratified by Barrow Neurological Institute (BNI) score for pain relief and BNI facial numbness score for facial hypesthesia. Results Sixty-seven patients met inclusion criteria and were included in this study. BNI score of I-IIIa was attained in 82% of patients at 3 months and 65% at 1 year following SRS. Distance from isocenter to REZ varied from 0 to 8.6 mm, with mean 1.94 ± 1.62 mm. Logistic regression of target-REZ distance against pain relief outcome (patients with score I-IIIa and IIIb-V) was insignificant at 3 months (p = 0.988), 6 months (p = 0.925), 9 months (p = 0.845), and 12 months (p = 0.547) post-operatively. Furthermore, no significant correlation was found with logistic regression of target-REZ distance with pain relief outcome (patients with score I and score II-IV) (p = 0.544). Conclusions The current analysis suggests that distance from REZ does not correlate with degree of post-operative pain relief or facial hypesthesia. Thus, targeting specific regions within the trigeminal nerve in relation to these anatomical characteristics may not afford any advantage from this perspective. Summary Stereotactic radiosurgery provides a noninvasive treatment modality to patients with medically refractory trigeminal neuralgia. The trigeminal REZ is a commonly used target due to its theoretical increased sensitivity to irradiation and neurovascular conflict. The current analysis suggests that distance from REZ does not correlate with degree of post-operative pain relief or facial hypesthesia. Targeting specific regions within the trigeminal nerve in relation to these anatomical characteristics may not afford any advantage from this perspective.
