Using Diffusion Tensor Imaging to Evaluate Microstructural Changes and Outcomes after Radiofrequency Rhizotomy of Trigeminal Nerves in Patients with Trigeminal Neuralgia

Abstract

Trigeminal neuralgia is characterized by facial pain that may be sudden, intense, and recurrent. Our aim was to investigate microstructural tissue changes of the trigeminal nerve in patients with trigeminal neuralgia resulting from neurovascular compression by diffusion tensor imaging, and to test the predictive value of diffusion tensor imaging for determining outcomes after radiofrequency rhizotomy. Forty-three patients with trigeminal neuralgia were recruited, and diffusion tensor imaging was performed before radiofrequency rhizotomy. By selecting the cisternal segment of the trigeminal nerve manually, we measured the volume of trigeminal nerve, fractional anisotropy, apparent diffusion coefficient, axial diffusivity, and radial diffusivity. The apparent diffusion coefficient and mean value of fractional anisotropy, axial diffusivity, and radial diffusivity were compared between the affected and normal side in the same patient, and were correlated with pre-rhizotomy and post-rhizotomy visual analogue scale pain scores. The results showed the affected side had significantly decreased fractional anisotropy, increased apparent diffusion coefficient and radial diffusivity, and no significant change of axial diffusivity. The volume of the trigeminal nerve on affected side was also significantly smaller. There was a trend of fractional anisotropy reduction and visual analogue scale pain score reduction (P = 0.072). The results suggest that demyelination without axonal injury, and decreased size of the trigeminal nerve, are the microstructural abnormalities of the trigeminal nerve in patients with trigeminal neuralgia caused by neurovascular compression. The application of diffusion tensor imaging in understanding the pathophysiology of trigeminal neuralgia, and predicting the treatment effect has potential and warrants further study.

Neurophysiological aspects of the trigeminal sensory system: an update

“…Advancements in imaging methodologies, e.g. diffusion tensor imaging and functional magnetic resonance imaging (fMRI), help us to understand the physiology and pathophysiology of the trigeminal system further (Mainero et al, 2007;Chen et al, 2016;Li et al, 2017). In this article, we aim to provide insights into and a thorough and clear overview of the most noteworthy studies and articles up to today on the neurophysiological sensory aspects of this complex neural system; important anatomic correlations will be reviewed where needed.…”

Fraction of anisotropy and apparent diffusion coefficient as diagnostic tools in trigeminal neuralgia

“…FA describes how much molecular displacements vary in space and is related to the presence of oriented structures [28]. ADC, expressed as square millimeter per second, characterizes the overall mean-squared displacement of molecules and the overall presence of obstacles to diffusion [2, 28].These evidences motivated several studies to examine structural abnormalities in the trigeminal nerve (TGN) of patients with TN using FA [5-7, 9, 10, 13-15, 17, 22-25, 30] and ADC [7,13,17,[23][24][25]. Most of the studies examining FA by comparing the affected and unaffected sides of patients and controls revealed a significant decrease in FA values [5-7, 9, 10, 14, 15, 17, 22-25].…”

“…Most of the studies examining FA by comparing the affected and unaffected sides of patients and controls revealed a significant decrease in FA values [5-7, 9, 10, 14, 15, 17, 22-25]. Chen et al, Leal et al, and Lummel et al reported a significant elevation in ADC values in the affected sides of patients [7,17,23]. Other three studies did not find differences in ADC values between affected and unaffected sides of patients and controls [13,24,25].…”

“…These evidences motivated several studies to examine structural abnormalities in the trigeminal nerve (TGN) of patients with TN using FA [5-7, 9, 10, 13-15, 17, 22-25, 30] and ADC [7,13,17,[23][24][25]. Most of the studies examining FA by comparing the affected and unaffected sides of patients and controls revealed a significant decrease in FA values [5-7, 9, 10, 14, 15, 17, 22-25].…”

“…With DTI, multiple images are collected so that the signal can be sensitized to diffusion in different directions, building up multiple measurements for each voxel in the brain [16]. Only six of the abovementioned studies were performed with 30 or more diffusion gradient-directions [5,7,9,10,17,30]. Other limits are the potential partial volume effects caused by the small size of the root bathed in cerebrospinal fluid and the artifactual images caused by involuntary patient motion.…”