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J Neurosurg. 2019 Jul 12:1-9. doi: 10.3171/2019.4.JNS19380. [Epub ahead of print]

Temporal disconnection between pain relief and trigeminal nerve microstructural changes after Gamma Knife radiosurgery for trigeminal neuralgia.

Author information

1Division of Brain, Imaging & Behaviour-Systems Neuroscience, Krembil Research Institute, and.
2Institute of Medical Science and.
3Department of Surgery, Faculty of Medicine, University of Toronto, Ontario, Canada.
4Division of Neurosurgery, Krembil Neuroscience Centre, Toronto Western Hospital, University Health Network; and.



Gamma Knife radiosurgery (GKRS) is a noninvasive surgical treatment option for patients with medically refractive classic trigeminal neuralgia (TN). The long-term microstructural consequences of radiosurgery and their association with pain relief remain unclear. To better understand this topic, the authors used diffusion tensor imaging (DTI) to characterize the effects of GKRS on trigeminal nerve microstructure over multiple posttreatment time points.


Ninety-two sets of 3-T anatomical and diffusion-weighted MR images from 55 patients with TN treated by GKRS were divided within 6-, 12-, and 24-month posttreatment time points into responder and nonresponder subgroups (≥ 75% and < 75% reduction in posttreatment pain intensity, respectively). Within each subgroup, posttreatment pain intensity was then assessed against pretreatment levels and followed by DTI metric analyses, contrasting treated and contralateral control nerves to identify specific biomarkers of successful pain relief.


GKRS resulted in successful pain relief that was accompanied by asynchronous reductions in fractional anisotropy (FA), which maximized 24 months after treatment. While GKRS responders demonstrated significantly reduced FA within the radiosurgery target 12 and 24 months posttreatment (p < 0.05 and p < 0.01, respectively), nonresponders had statistically indistinguishable DTI metrics between nerve types at each time point.


Ultimately, this study serves as the first step toward an improved understanding of the long-term microstructural effect of radiosurgery on TN. Given that FA reductions remained specific to responders and were absent in nonresponders up to 24 months posttreatment, FA changes have the potential of serving as temporally consistent biomarkers of optimal pain relief following radiosurgical treatment for classic TN.


CBZ = carbamazepine; DTI = diffusion tensor imaging; FA = fractional anisotropy; GKRS = Gamma Knife radiosurgery; Gamma Knife radiosurgery; NRS = numerical rating scale; TN = trigeminal neuralgia; chronic facial pain; diffusion tensor imaging; stereotactic radiosurgery; surgical outcomes; trigeminal nerve microstructure; trigeminal neuralgia


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