Diffusion tensor imaging for assessment of microstructural changes associate with treatment outcome at one-year after radiofrequency Rhizotomy in trigeminal neuralgia

Abstract

Background Trigeminal neuralgia (TN) is characterized by facial pain that may be sudden, intense, and recurrent. Neurosurgical interventions, such as radiofrequency rhizotomy, can relieve TN pain, but their mechanisms and effects are unknown. The aim of the present study was to investigate the microstructural tissue changes of the trigeminal nerve (TGN) in patients with TN after they underwent radiofrequency rhizotomy. Methods Thirty-seven patients with TN were recruited, and diffusion tensor imaging was obtained before and two weeks after radiofrequency rhizotomy. By manually selecting the cisternal segment of the TGN, we measured the volume of the TGN, fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity (AD), and radial diffusivity (RD). The TGN volume and mean value of the DTI metrics of the post-rhizotomy lesion side were compared with those of the normal side and those of the pre-rhizotomy lesion side, and they were correlated to the post-rhizotomy visual analogue scale (VAS) pain scores after a one-year follow-up. Results The alterations before and after rhizotomy showed a significantly increased TGN volume and FA, and a decreased ADC, AD, and RD. The post-rhizotomy lesion side showed a significantly decreased TGN volume, FA, and AD compared with the normal side; however, no significant difference in the ADC and RD were found between the groups. The TGN volume was significantly higher in the non-responders than in the responders ( P = 0.016). Conclusion Our results may reflect that the effects of radiofrequency rhizotomy in TN patients include axonal damage with perineural edema and that prolonged swelling associated with recurrence might be predicted by MRI images. Further studies are necessary to understand how DTI metrics can quantitatively represent the pathophysiology of TN and to examine the application of DTI in the treatment of TN.

Trigeminal Nerve White Matter Fiber Abnormalities in Primary Trigeminal Neuralgia: A Diffusion Spectrum Imaging Study

“…DSI is a valuable tool for central nervous system imaging as it can be used to visualize the structural details of white matter bundles in multiple directions ( 14 , 28 – 30 ). Similar to previous studies ( 6 , 7 ), in our study, the FA value of trigeminal nerve on the affected side of TN patients was lower than that on the unaffected side and the decrease of FA value indicated that the integrity of white matter fiber bundle was damaged. However, in our study, AD, RD, and MD in the patient group did not increase significantly as previous studies.…”

“…As a non-invasive magnetic resonance imaging (MRI) technique to evaluate the integrity of white matter, diffusion tensor imaging (DTI) can indirectly reflect the integrity of nerve fiber bundles by measuring the diffusion movement of water molecules ( 5 ), thus providing new insights into the etiology of TN. Previous studies ( 6 , 7 ) have shown that in patients with TN, DTI parameters such as fractional anisotropy (FA) decreased significantly and axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) increased significantly. However, some studies ( 8 , 9 ) argued different or even opposite opinions of the changes of DTI metrics values between affected and unaffected sides in patients and controls.…”

High spatial resolution nerve‐specific DTI protocol outperforms whole‐brain DTI protocol for imaging the trigeminal nerve in healthy individuals

“…The resulting partial volume effect with adjacent CSF will reduce FA and elevate MD erroneously. For example, MD values in the unaffected CNV of TN patients have ranged from 1.2‐4.3 x 10 −3 mm 2 /s, 4,5,7,11,14–17 which is 1.5‐5–fold greater than that expected of adult white matter (~0.8 x 10 −3 mm 2 /s). However, the effects of partial volume and CSF contamination may be reduced by improving spatial resolution.…”

“…Many previous nerve DTI studies of CNV in TN have employed low resolution “whole‐brain” acquisition protocols with thick slices of 2 mm or greater, yielding large voxel volumes of 2 x 2 x 2 = 8 mm 3 5,7,14 or 1.9 x 1.9 x 3 = 10.8 mm 3 4,6,15,16 relative to a comparatively small structure. The resulting partial volume effect with adjacent CSF will reduce FA and elevate MD erroneously.…”

Application of diffusion tensor imaging in detecting microstructural alteration of the trigeminal nerve root in patients with classical trigeminal neuralgia without neurovascular compression

“…[16] Also recent study reported that increased trigeminal nerves volume and FA, and a decreased ADC, AD, and RD represent the pathophysiology of TN, and decreased trigeminal nerves volume, FA, and AD compared with the normal side after a one-year follow-up of partial rhizotomy (PR) of sensory root of trigeminal nerve. [3] These studies provided us information and concepts that DTI and its diffusivity metrics may have clinical signi cance for microstructural change and prognosis evaluation.…”