Tractography Delineates Microstructural Changes in the Trigeminal Nerve after Focal Radiosurgery for Trigeminal Neuralgia

Abstract

PurposeFocal radiosurgery is a common treatment modality for trigeminal neuralgia (TN), a neuropathic facial pain condition. Assessment of treatment effectiveness is primarily clinical, given the paucity of investigational tools to assess trigeminal nerve changes. Since diffusion tensor imaging (DTI) provides information on white matter microstructure, we explored the feasibility of trigeminal nerve tractography and assessment of DTI parameters to study microstructural changes after treatment. We hypothesized that trigeminal tractography provides more information than 2D-MR imaging, allowing detection of unique, focal changes in the target area after radiosurgery. Changes in specific diffusivities may provide insight into the mechanism of action of radiosurgery on the trigeminal nerve.Methods and MaterialsFive TN patients (4 females, 1 male, average age 67 years) treated with Gamma Knife radiosurgery, 80 Gy/100% isodose line underwent 3Tesla MR trigeminal nerve tractography before and sequentially up to fourteen months after treatment. Fractional anisotropy (FA), radial (RD) and axial (AD) diffusivities were calculated for the radiosurgical target area defined as the region-of-interest. Areas outside target and the contralateral nerve served as controls.ResultsTrigeminal tractography accurately detected the radiosurgical target. Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, demonstrating highly focal changes after treatment. RD but not AD changed markedly, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive than conventional gadolinium-enhanced post-treatment MR, since FA changes were detected regardless of trigeminal nerve enhancement. In subjects with long term follow-up, recovery of FA/RD correlated with pain recurrence.ConclusionsDTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN. This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.

Microstructural alterations in trigeminal neuralgia determined by diffusion tensor imaging are independent of symptom duration, severity, and type of neurovascular conflict

“…Our current protocol does not enable reliable follow-up DTI analyses after MVD (as it is described after radiosurgery), 14 which most likely is due to the artifacts caused by the surgical procedure itself.…”

Gamma Knife for Functional Diseases

“…Radiosurgery has been demonstrated to induce demyelination both in experimental models [18] and in autopsy [19]. This finding has been confirmed by tractography examinations [20].…”

“…, ventrointermediate nucleus (VIM), capsulotomy, trigeminal neuralgia (TN), etc.] with a high dose (maximum 80-140 Gy) or to target a large volume of tissue (i.e., 5-9 cc in epilepsy radiosurgery) with a moderate dose (17)(18)(19)(20)(21)(22)(23)(24) Gy at the marginal isodose).…”

Is There a Magnetic Resonance Imaging-Discernible Cause for Trigeminal Neuralgia? A Structured Review

“…Of the studies examining FA by comparing the affected and unaffected sides in patients and controls, two [6, 35] found significant decreases in FA on both sides while four of the studies [27, 32, 36, 42] found a significantly lower FA only in the affected side. Hodaie et al [38] and DeSouza et al [27] compared FA values as measured before and after surgery, with Hodaie’s study recording a significant decrease in FA after surgery and DeSouza’s study describing a significant increase in FA after surgery.…”

“…Two studies [35, 36] found significant increases in the RD when comparing patients to controls in both their affected and unaffected sides, while another two studies [27, 42] measured significance on the affected side of the patients compared to controls, and another study [41] did not find a significant difference in either category. Hodaie et al [38] and DeSouza et al [27] found significant differences in RD when comparing the affected side before and after surgery; Hodaie found a significant increase while DeSouza found a significant decrease.…”