Structural Magnetic Resonance Imaging Can Identify Trigeminal System Abnormalities in Classical Trigeminal Neuralgia

Cognitive Decline in Patients With Trigeminal Neuralgia: A Resting-State fMRI Study

OBJECTIVE

This study utilized functional magnetic resonance imaging (fMRI) data to investigate cognitive function changes in trigeminal neuralgia (TN) patients and healthy controls (HCs), and to elucidate the potential mechanism.

MATERIALS AND METHODS

The cognitive function of 34 patients with TN and 30 HCs was evaluated. Afterward, we calculated the amplitude of low-frequency fluctuations (ALFFs), regional homogeneity (ReHo), and degree centrality (DC). These metrics were correlated with cognitive performance using the Spearman correlation analysis.

RESULTS

Patients with TN exhibited diminished cognitive performance compared to HCs. Increased mean ALFF (mALFF) levels were detected in the right temporal pole, superior temporal gyrus, and right insula in individuals with TN. These increases were negatively correlated with cognitive function. In contrast, decreased mALFF values were observed in the right lingual gyrus, bilateral calcarine, and left middle occipital gyrus, which were associated with improved cognitive function. Increased DC values were found in various areas, such as the right temporal pole, superior temporal gyrus, right opercular inferior frontal gyrus, bilateral medial superior frontal gyrus, left supplementary motor area, left anterior cingulum, and right middle cingulum in individuals with TN. These values negatively correlated with cognitive performance.

CONCLUSION

TN patients exhibited impairments in multiple cognitive areas, such as attention, memory, executive function, visual perception and executive ability, information processing speed, and motor speed. The metrics ALFF and DC exhibited alterations in TN patients, suggesting that cognitive impairments may be linked to decreased functional activity in specific brain regions. Concurrently, certain cerebral regions may exhibit increased functional activity as a compensatory response to cognitive deficits. These findings hold significant theoretical value and clinical application potential, providing novel methodologies and perspectives for early diagnosis, personalized treatment, and efficacy evaluation. Such advancements are poised to enhance the overall treatment outcomes and quality of life for TN patients.

Automatic Segmentation of the Cisternal Segment of Trigeminal Nerve on MRI Using Deep Learning

Purpose: Accurate segmentation of the cisternal segment of the trigeminal nerve plays a critical role in identifying and treating different trigeminal nerve-related disorders, including trigeminal neuralgia (TN). However, the current manual segmentation process is prone to interobserver variability and consumes a significant amount of time. To overcome this challenge, we propose a deep learning-based approach, U-Net, that automatically segments the cisternal segment of the trigeminal nerve. Methods: To evaluate the efficacy of our proposed approach, the U-Net model was trained and validated on healthy control images and tested in on a separate dataset of TN patients. The methods such as Dice, Jaccard, positive predictive value (PPV), sensitivity (SEN), center-of-mass distance (CMD), and Hausdorff distance were used to assess segmentation performance. Results: Our approach achieved high accuracy in segmenting the cisternal segment of the trigeminal nerve, demonstrating robust performance and comparable results to those obtained by participating radiologists. Conclusion: The proposed deep learning-based approach, U-Net, shows promise in improving the accuracy and efficiency of segmenting the cisternal segment of the trigeminal nerve. To the best of our knowledge, this is the first fully automated segmentation method for the trigeminal nerve in anatomic MRI, and it has the potential to aid in the diagnosis and treatment of various trigeminal nerve-related disorders, such as TN.

Advanced neuroimaging of the trigeminal nerve and the whole brain in trigeminal neuralgia: a systematic review

ABSTRACT

For trigeminal neuralgia (TN), a major role of imaging is to identify the causes, but recent studies demonstrated structural and microstructural changes in the affected nerve. Moreover, an increasing number of studies have reported central nervous system involvement in TN. In this systematic review, recent quantitative magnetic resonance imaging (MRI) studies of the trigeminal nerve and the brain in patients with TN were compiled, organized, and discussed, particularly emphasizing the possible background mechanisms and the interpretation of the results. A systematic search of quantitative MRI studies of the trigeminal nerve and the brain in patients with TN was conducted using PubMed. We included the studies of the primary TN published during 2013 to 2023, conducted for the assessment of the structural and microstructural analysis of the trigeminal nerve, and the structural, diffusion, and functional MRI analysis of the brain. Quantitative MRI studies of the affected trigeminal nerves and the trigeminal pathway demonstrated structural/microstructural alterations and treatment-related changes, which differentiated responders from nonresponders. Quantitative analysis of the brain revealed changes in the brain areas associated with pain processing/modulation and emotional networks. Studies of the affected nerve demonstrated evidence of demyelination and axonal damage, compatible with pathological findings, and have shown its potential value as a tool to assess treatment outcomes. Quantitative MRI has also revealed the possibility of dynamic microstructural, structural, and functional neuronal plasticity of the brain. Further studies are needed to understand these complex mechanisms of neuronal plasticity and to achieve a consensus on the clinical use of quantitative MRI in TN.

Altered structure and functional connection of subcortical gray matter in female patients with classical trigeminal neuralgia

The etiology of classical trigeminal neuralgia (CTN) is still unclear. A better understanding of the cerebral structural and functional changes in female patients with CTN may provide important novel insights into the pathophysiologic mechanisms of female CTN. A total 37 female CTN patients were included and referred to MRI scans, comprising with 19 left CTN and 18 right CTN patients. We analyzed the volume and shape of subcortical gray matter (GM), and the functional connectivity (FC) between the accumbens nucleus (NAc) and whole brain in right and left CTN patients respectively. We found left CTN patients had a reduced right NAc volume compared to controls, similarly, the right CTN had the decreased volume in the left NAc. Vertex-wise shapes of right NAc in left CTN patients showed significant regional shape deformation on the anterior, medial and ventroposterior aspects, in contrast, left NAc of right CTN patients showed significant regional shape deformation on the anterior and posterior aspect. Furthermore, patients with left CTN showed significantly lower FC between the right NAc and right orbitofrontal cortex than control subjects. The volume of NAc in all CTN was significantly related to the perception of present pain intensity. The CTN might be majorly caused by volume reduction in NAc. A greater understanding of the neurobiological basis of pain-related changes in NAc will provide the knowledge for the development of novel NAc based therapeutic targets for pain management or even prevention in CTN patients.

[Surgical treatment of trigeminal pain]

Surgical procedures for treating neuropathic pain, including trigeminal neuralgia (TGN), are categorized into three groups: decompression, ablation, and neuromodulation. Microvascular decompression is the only causal therapy for TGN, applicable favorably in cases of classical TGN due to a vascular nerve conflict. Ablative procedures include both percutaneous and radiosurgical methods, which are mainly used for idiopathic trigeminal neuralgia. For irreversible neuropathies of the trigeminal nerve, the algorithm for other neuropathic pain conditions should be considered, along with the potential use of neuromodulatory techniques. When selecting a therapy, diagnosis, medication side effects, individual patient risks, and treatment outcomes must all be taken into account (current S1 guideline from the German Society of Neurology).

Pre-treatment DTI markers: predicting clinical outcomes in microvascular decompression for classic trigeminal neuralgia - a systematic review

BACKGROUND AND PURPOSE

Trigeminal neuralgia (TN) is a severe chronic pain condition, typically affecting patients over 50-year-old, caused by the compression of the nerve at the root entry zone (REZ) by blood vessels. While the diagnosis is clinical, advanced imaging like diffusion tensor imaging (DTI) is crucial to identify underlying causes and assessing nerve damage. DTI may help develop neuroimaging markers to improve understanding of TN and predict surgical outcomes. The goal of the present systematic review is to evaluate the effectiveness of DTI and tractography in order to better assess treatment planning and outcome prediction through the analysis of trigeminal nerve alterations.

METHODS

The authors conducted a systematic review and meta-analysis of the literature to compare radiological parameters identified in pre- and post-operative MRI with DTI sequences, including fractional anisotropy (FA), quantity of anisotropy (QA), radial diffusivity (RD), and to correlate these findings with post-operative clinical outcomes. A comprehensive search of the PubMed and Scopus databases was carried out for studies published between April 2010 and January 2024.

RESULTS

This review included 11 studies and 603 patients. Of the 363 patients with trigeminal neuralgia (TN), 193 underwent microvascular decompression (MVD), with 72.5% showing clinical improvement and 27.5% not improving, possibly due to chronic nerve damage. Four studies assessed radiological parameters before and after MVD, while two focused only on post-MVD data. The mean fractional anisotropy (FA) in affected nerves increased from 0.328 before MVD to 0.382 afterward. Five studies did not report postoperative outcomes, just comparing radiological parameters in TN patients versus healthy controls.

CONCLUSIONS

Recent studies show that MRI-DTI parameters, including FA, RD, and QA, are useful for diagnosing trigeminal neuralgia and predicting treatment outcomes. Lower FA and higher RD values indicate better results after surgery. More research is mandatory to guide treatment decisions and enhance patients' care.

Regional and interregional functional and structural brain abnormalities in neuropathic pain

Neuropathic pain is a severe form of chronic pain due to a lesion or disease of the somatosensory nervous system. Here we provide an overview of the neuroimaging approaches that can be used to assess brain abnormalities in a chronic pain condition, with particular focus on people with neuropathic pain and then summarize the findings of studies that applied these methodologies to study neuropathic pain. First, we review the most commonly used approaches to examine grey and white matter abnormalities using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) and then review functional neuroimaging techniques to measure regional activity and inter-regional communication using functional MRI, electroencephalography (EEG) and magnetoencephalography (MEG). In neuropathic pain the most prominent structural abnormalities have been found to be in the primary somatosensory cortex, insula, anterior cingulate cortex and thalamus, with differences in volume directionality linked to neuropathic pain symptomology. Functional connectivity findings related to treatment outcome point to a potential clinical utility. Some prominent abnormalities in neuropathic pain identified with EEG and MEG throughout the dynamic pain connectome are slowing of alpha activity and higher regional oscillatory activity in the theta and alpha band, lower low beta and higher high beta band power. Finally, connectivity and coupling findings placed into context how regional abnormalities impact the networks and pathways of the dynamic pain connectome. Overall, functional and structural neuroimaging have the potential to identify predictive biomarkers that can be used to guide development of personalized pain management of neuropathic pain.

Altered Brain Structure in Hemifacial Spasm Patients: A Multimodal Brain Structure Study

Objective

Hemifacial spasm (HFS) is a clinical neurosurgical disease, which brain structural alterations caused by HFS remain a topic of debate. We evaluated changes in brain microstructure associated with HFS and observed their relevance to clinical characteristics.

Methods

We enrolled 72 participants. T1-weighted structural and diffusion tensor images were collected from all participants using 3.0T magnetic resonance equipment. Voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) were used to identify changes in gray matter volume (GMV) and disruptions in white matter (WM) integrity. The severity of the spasms was graded using the Cohn scale.

Results

VBM analysis revealed that the GMV was significantly reduced in the left Thalamus and increased GMV in the right Cerebellum IV-V of the HFS group. TBSS analysis showed that FA in the left superior longitudinal fasciculus (SLF) of the HFS group was significantly increased. GMV in the thalamus showed a negative correlation with disease duration and Cohn grade, while FA in the left SLF had a positive correlation with both the disease duration and Cohn grade.

Conclusion

We identified regions with altered GMV in HFS patients. Additionally, we determined that FA in the left SLF might serve as a significant neural indicator of HFS.

Impact of microvascular decompression on wall shear stress in responsible arteries in trigeminal neuralgia and hemifacial spasm

Microvascular decompression (MVD) has proven efficacy in trigeminal neuralgia (TN) and hemifacial spasm (HFS). This study utilized computational fluid dynamics (CFD) to investigate the impact of MVD on wall shear stress (WSS) of responsible arteries (RAs) at the neurovascular contact (NVC). A total of 21 cases (10 TN, 11 HFS) were analyzed, involving RAs at NVC validated through intraoperative photographs. Hemodynamic parameters (WSS, vessel diameter, flow rate, pressure drop) was calculated using CFD for the RAs based on 3D silent-magnetic resonance angiograms. The NVC was segmented into NVC-proximal, NVC-site, and NVC-distal portions using simulated 3D CFD images that correlated with surgical observations. WSS ratios of NVC-site to NVC-proximal (NVC-site/proximal) was calculated both before and after MVD. Prior to MVD, WSS in the RA at the NVC displayed a peaked curve with a maximum at NVC-site; however, post MVD, it presented a smooth curve without peaks. The WSS ratio exhibited a significant decrease after MVD. The impact of MVD on WSS of RAs at NVC was evaluated in both TN and HFS cases. Analyzing the hemodynamics of RAs through CFD and identifying WSS peaks at NVC portions before MVD provided a more detailed and localized understanding of the morphologically depicted NVC.

Exploring biomarkers in trigeminal neuralgia patients operated with microvascular decompression: A comparison with multiple sclerosis patients and non-neurological controls

BACKGROUND

Trigeminal neuralgia (TN) is a severe facial pain condition often associated with a neurovascular conflict. However, neuroinflammation has also been implicated in TN, as it frequently co-occurs with multiple sclerosis (MS).

METHODS

We analysed protein expression levels of TN patients compared to MS patients and controls. Proximity Extension Assay technology was used to analyse the levels of 92 proteins with the Multiplex Neuro-Exploratory panel provided by SciLifeLab, Uppsala, Sweden. Serum and CSF samples were collected from TN patients before (n = 33 and n = 27, respectively) and after (n = 28 and n = 8, respectively) microvascular decompression surgery. Additionally, we included samples from MS patients (n = 20) and controls (n = 20) for comparison.

RESULTS

In both serum and CSF, several proteins were found increased in TN patients compared to either MS patients, controls, or both, including EIF4B, PTPN1, EREG, TBCB, PMVK, FKBP5, CD63, CRADD, BST2, CD302, CRIP2, CCL27, PPP3R1, WWP2, KLB, PLA2G10, TDGF1, SMOC1, RBKS, LTBP3, CLSTN1, NXPH1, SFRP1, HMOX2, and GGT5. The overall expression of the 92 proteins in postoperative TN samples seems to shift towards the levels of MS patients and controls in both serum and CSF, as compared to preoperative samples. Interestingly, there was no difference in protein levels between MS patients and controls.

CONCLUSIONS

We conclude that TN patients showed increased serum and CSF levels of specific proteins and that successful surgery normalizes these protein levels, highlighting its potential as an effective treatment. However, the similarity between MS and controls challenges the idea of shared pathophysiology with TN, suggesting distinct underlying mechanisms in these conditions.

SIGNIFICANCE

This study advances our understanding of trigeminal neuralgia (TN) and its association with multiple sclerosis (MS). By analysing 92 protein biomarkers, we identified distinctive molecular profiles in TN patients, shedding light on potential pathophysiological mechanisms. The observation that successful surgery normalizes many protein levels suggests a promising avenue for TN treatment. Furthermore, the contrasting protein patterns between TN and MS challenge prevailing assumptions of similarity between the two conditions and point to distinct pathophysiological mechanisms.

Trigeminal neuralgia

Trigeminal neuralgia (TN) is a facial pain disorder characterized by intense and paroxysmal pain that profoundly affects quality of life and presents complex challenges in diagnosis and treatment. TN can be categorized as classical, secondary and idiopathic. Epidemiological studies show variable incidence rates and an increased prevalence in women and in the elderly, with familial cases suggesting genetic factors. The pathophysiology of TN is multifactorial and involves genetic predisposition, anatomical changes, and neurophysiological factors, leading to hyperexcitable neuronal states, central sensitization and widespread neural plasticity changes. Neurovascular compression of the trigeminal root, which undergoes major morphological changes, and focal demyelination of primary trigeminal afferents are key aetiological factors in TN. Structural and functional brain imaging studies in patients with TN demonstrated abnormalities in brain regions responsible for pain modulation and emotional processing of pain. Treatment of TN involves a multifaceted approach that considers patient-specific factors, including the type of TN, with initial pharmacotherapy followed by surgical options if necessary. First-line pharmacological treatments include carbamazepine and oxcarbazepine. Surgical interventions, including microvascular decompression and percutaneous neuroablative procedures, can be considered at an early stage if pharmacotherapy is not sufficient for pain control or has intolerable adverse effects or contraindications.

Altered intra- and inter-network functional activity among migraine, chronic migraine, and trigeminal neuralgia

OBJECTIVE

This study aimed to investigate the specific manifestations and differences in brain network activity and functional connectivity between brain networks in patients with trigeminal neuralgia and migraine, aiming to reveal the neural basis of these two diseases.

BACKGROUND

Head and facial pain, including trigeminal neuralgia and migraine, is prevalent globally. However, the underlying neural mechanisms of these conditions remain unclear. Resting-state functional connectivity studies based on independent component analysis (ICA) may offer new insights into these diseases.

METHODS

The study involved 23 chronic migraine, 37 episodic migraine, 21 trigeminal neuralgia patients, and 33 age- and gender-matched controls. Resting-state functional magnetic resonance imaging was performed, and five sets of brain network components were extracted through ICA. Neuronal activity indicators were calculated for each participant's independent components, including amplitudes of low-frequency fluctuation (ALFF) and regional homogeneity (ReHo). Functional connectivity was also assessed and compared among the four groups.

RESULTS

Trigeminal neuralgia patients showed reduced ALFF in the dorsal attention network versus episodic migraine patients and controls. Both trigeminal neuralgia and chronic migraine patients had decreased ReHo in this network. Migraine patients had weaker connectivity between the default mode and visual networks than controls. Trigeminal neuralgia patients also showed higher connectivity between the somatosensory motor and dorsal attention networks. Compared to episodic migraine, trigeminal neuralgia, and chronic migraine patients had increased connectivity between the visual and dorsal attention networks.

CONCLUSION

The study provides evidence that long-term chronic head and facial pain may contribute to abnormalities in the activation and connectivity of the dorsal attention network. Compared to migraine patients, trigeminal neuralgia patients exhibit abnormal brain network connectivity, particularly within the somatomotor network, which may explain the presence of significant "trigger points." These findings offer new perspectives for understanding the characteristics of different head and facial pain subtypes.

Atlas orthogonal chiropractic management of trigeminal neuralgia: A series of case reports

CONTEXT

Trigeminal neuralgia is a debilitating facial pain condition. Upper cervical chiropractic care has been mentioned as a possible solution OBJECTIVE: To determine the effects of Atlas Orthogonal upper cervical chiropractic technique adjustments on trigeminal neuralgia sufferers DESIGN: Case series SETTING: A private chiropractic practice PARTICIPANTS: Five persons with chronic, severe, daily trigeminal neuralgia pain, radiological findings of significant head tilt, pain upon upper cervical palpation, and supine leg length inequality INTERVENTIONS: Up to two consultations and/or Atlas Orthogonal adjustments a week for eight weeks OUTCOME MEASURES: Self-reported reduction in trigeminal neuralgia pain and changes in radiological findings, sensitivity to upper cervical palpation, and leg length inequality RESULTS: Four participants reported reduced trigeminal neuralgia pain, including two with complete cessation of pain. Three participants reduced medication dosages. One reported no change.

Brain imaging signatures of neuropathic facial pain derived by artificial intelligence

Advances in neuroimaging have permitted the non-invasive examination of the human brain in pain. However, a persisting challenge is in the objective differentiation of neuropathic facial pain subtypes, as diagnosis is based on patients' symptom descriptions. We use artificial intelligence (AI) models with neuroimaging data to distinguish subtypes of neuropathic facial pain and differentiate them from healthy controls. We conducted a retrospective analysis of diffusion tensor and T1-weighted imaging data using random forest and logistic regression AI models on 371 adults with trigeminal pain (265 classical trigeminal neuralgia (CTN), 106 trigeminal neuropathic pain (TNP)) and 108 healthy controls (HC). These models distinguished CTN from HC with up to 95% accuracy, and TNP from HC with up to 91% accuracy. Both classifiers identified gray and white matter-based predictive metrics (gray matter thickness, surface area, and volume; white matter diffusivity metrics) that significantly differed across groups. Classification of TNP and CTN did not show significant accuracy (51%) but highlighted two structures that differed between pain groups-the insula and orbitofrontal cortex. Our work demonstrates that AI models with brain imaging data alone can differentiate neuropathic facial pain subtypes from healthy data and identify regional structural indicates of pain.

Alterations of degree centrality and functional connectivity in classic trigeminal neuralgia

Objectives

Recent neuroimaging studies have indicated a wide range of structural and regional functional alterations in patients with classic trigeminal neuralgia (CTN). However, few studies have focused on the intrinsic functional characteristics of network organization in the whole brain. Therefore, the present study aimed to characterize the potential intrinsic dysconnectivity pattern of the whole brain functional networks at the voxel level using the degree centrality (DC) analysis in CTN patients.

Methods

Thirty-four patients with CTN and twenty-nine well-matched healthy controls (HCs) participated in this study. All subjects underwent resting-state functional magnetic resonance imaging (rs-MRI) examination and clinical and neuropsychologic assessments. DC is a graph theory-based measurement that represents the overall functional connectivity (FC) numbers between one voxel and other brain voxels. We first investigated brain regions exhibiting abnormal DC, and further identified their perturbation on FC with other brain regions using a seed-based FC analysis in patients with CTN. In addition, correlation analyses were performed to evaluate the relationship between the abnormal DC value and clinical variables in CTN patients.

Results

Compared with the HCs, the patients with CTN exhibited significantly greater DC values in the right pallidum and right putamen, and lower DC values in the right lingual gyrus, right calcarine sulcus, left paracentral lobule, and left midcingulate cortex. A further seed-based FC analysis revealed that the right lingual gyrus showed decreased FC within the visual network and with other core brain networks, including the sensorimotor network, default mode network, and salience network, relative to HCs. Additionally, the left midcingulate cortex exhibited decreased FC within the middle cingulate cortex and the visual network in CTN patients. Moreover, the DC value in the left midcingulate cortex was negatively correlated with the illness duration.

Conclusion

The present study shows that CTN patients exhibited specific functional connectivity network alterations in the basal ganglia, visual network, and salience network, which may reflect the aberrant neural network communication in pain processing and modulation. These findings may provide novel insight for understanding the mechanisms of pain chronicity in CTN patients.

Vestibular paroxysmia entails vestibular nerve function, microstructure and endolymphatic space changes linked to root-entry zone neurovascular compression

Combining magnetic resonance imaging (MRI) sequences that permit the determination of vestibular nerve angulation (NA = change of nerve caliber or direction), structural nerve integrity via diffusion tensor imaging (DTI), and exclusion of endolymphatic hydrops (ELH) via delayed gadolinium-enhanced MRI of the inner ear (iMRI) could increase the diagnostic accuracy in patients with vestibular paroxysmia (VP). Thirty-six participants were examined, 18 with VP (52.6 ± 18.1 years) and 18 age-matched with normal vestibulocochlear testing (NP 50.3 ± 16.5 years). This study investigated whether (i) NA, (ii) DTI changes, or (iii) ELH occur in VP, and (iv) to what extent said parameters relate. Methods included vestibulocochlear testing and MRI data analyses for neurovascular compression (NVC) and NA verification, DTI and ELS quantification. As a result, (i) NA increased NVC specificity. (ii) DTI structural integrity was reduced on the side affected by VP (p < 0.05). (iii) 61.1% VP showed mild ELH and higher asymmetry indices than NP (p > 0.05). (iv) "Disease duration" and "total number of attacks" correlated with the decreased structural integrity of the affected nerve in DTI (p < 0.001). NVC distance within the nerve's root-entry zone correlated with nerve function (Roh = 0.72, p < 0.001), nerve integrity loss (Roh = - 0.638, p < 0.001), and ELS volume (Roh = - 0.604, p < 0.001) in VP. In conclusion, this study is the first to link eighth cranial nerve function, microstructure, and ELS changes in VP to clinical features and increased vulnerability of NVC in the root-entry zone. Combined MRI with NVC or NA verification, DTI and ELS quantification increased the diagnostic accuracy at group-level but did not suffice to diagnose VP on a single-subject level due to individual variability and lack of diagnostic specificity.

Altered Structural and Functional Abnormalities of Hippocampus in Classical Trigeminal Neuralgia: A Combination of DTI and fMRI Study

Purpose

Diffusion tensor imaging (DTI) and resting-state functional magnetic resonance imaging (rs-fMRI) were applied to speculate the altered structural and functional abnormalities within the hippocampus in classical trigeminal neuralgia (CTN) patients by detecting the alteration of apparent diffusion coefficient (ADC), fractional anisotropy (FA), and regional homogeneity (ReHo). Patients and Methods. Multimodal MRI dataset (DTI and fMRI) and clinical indices (pain and neuropsychological scores) were collected in 27 CTN patients and 27 age- and gender-matched healthy controls (HC). Two independent-sample t-tests were performed to compare the ADC, FA, and ReHo values in hippocampus areas between CTN patients and HC. Correlation analyses were applied between all the DTI and fMRI parameters within the hippocampus and the VAS (visual analog scale), MoCA (Montreal cognitive assessment), and CDR (clinical dementia rating) scores.

Results

CTN patients showed a significantly increased FA values in the right hippocampus (t = 2.387, P = 0.021) and increased ReHo values in the right hippocampus head (voxel P < 0.001, cluster P < 0.05, FDR correction) compared with HC. A positively significant correlation was observed between the ReHo values and MOCA scores in the right hippocampus head; FA values were also positively correlated with MOCA scores in the right hippocampus.

Conclusion

CTN patients demonstrated an abnormality of structures and functions in the hippocampus, which may help to provide novel insights into the neuropathologic change related to the pain-related dysfunction of CTN.

Structural and Functional Brain Changes in Patients With Classic Trigeminal Neuralgia: A Combination of Voxel-Based Morphometry and Resting-State Functional MRI Study

Objectives

Brain structural and functional abnormalities have been separately reported in patients with classic trigeminal neuralgia (CTN). However, whether and how the functional deficits are related to the structural alterations remains unclear. This study aims to investigate the anatomical and functional deficits in patients with CTN and explore their association.

Methods

A total of 34 patients with CTN and 29 healthy controls (HCs) with age- and gender-matched were recruited. All subjects underwent structural and resting-state functional magnetic resonance imaging (fMRI) scanning and neuropsychological assessments. Voxel-based morphometry (VBM) was applied to characterize the alterations of gray matter volume (GMV). The amplitude of low-frequency fluctuation (ALFF) method was used to evaluate regional intrinsic spontaneous neural activity. Further correlation analyses were performed between the structural and functional changes and neuropsychological assessments.

Results

Compared to the HCs, significantly reduced GMV was revealed in the right hippocampus, right fusiform gyrus (FFG), and temporal-parietal regions (the left superior/middle temporal gyrus, left operculo-insular gyrus, left inferior parietal lobule, and right inferior temporal gyrus) in patients with CTN. Increased functional activity measured by zALFF was observed mainly in the limbic system (the bilateral hippocampus and bilateral parahippocampal gyrus), bilateral FFG, basal ganglia system (the bilateral putamen, bilateral caudate, and right pallidum), left thalamus, left cerebellum, midbrain, and pons. Moreover, the right hippocampus and FFG were the overlapped regions with both functional and anatomical deficits. Furthermore, GMV in the right hippocampus was negatively correlated with pain intensity, anxiety, and depression. GMV in the right FFG was negatively correlated with illness duration. The zALFF value in the right FFG was positively correlated with anxiety.

Conclusion

Our results revealed concurrent structural and functional changes in patients with CTN, indicating that the CTN is a brain disorder with structural and functional abnormalities. Moreover, the overlapping structural and functional changes in the right hippocampus and FFG suggested that anatomical and functional changes might alter dependently in patients with CTN. These findings highlight the vital role of hippocampus and FFG in the pathophysiology of CTN.

White Matter Diffusion Properties in Chronic Temporomandibular Disorders: An Exploratory Analysis

Objective

To determine differences in diffusion metrics in key white matter (WM) tracts between women with chronic temporomandibular disorders (TMDs) and age- and sex-matched healthy controls.

Design

Cross sectional study compared diffusion metrics between groups and explored their associations with clinical variables in subjects with TMDs.

Methods

In a total of 33 subjects with TMDs and 33 healthy controls, we performed tractography to obtain diffusion metrics (fractional anisotropy [FA], mean diffusivity [MD], radial diffusivity [RD], and axial diffusivity [AD]) from the cingulum near the cingulate gyrus (CGC), the cingulum near the hippocampus (CGH), the fornix, the anterior limb of the internal capsule (ALIC), the posterior limb of the internal capsule (PLIC), and the uncinate fasciculus (UF). We compared diffusion metrics across groups and explored the relationships between diffusion metrics and clinical measures (pain chronicity and intensity, central sensitization, somatization, depression, orofacial behavior severity, jaw function limitations, disability, and interference due to pain) in subjects with TMDs.

Results

We observed differences in diffusion metrics between groups, primarily in the right side of the brain, with the right CGC having lower FA and the right UF having lower FA and higher MD and RD in subjects with TMDs compared to healthy controls. No clinical measures were consistently associated with diffusion metrics in subjects with TMDs.

Conclusion

The UF showed potential microstructural damage in subjects with TMDs, but further studies are needed to confirm any associations between diffusion changes and clinical measures.

The application of magnetic resonance imaging (MRI) for the prediction of surgical outcomes in trigeminal neuralgia

Trigeminal neuralgia (TN) is a severe facial pain disorder that often requires surgical treatment. Neurovascular compression (NVC) has been widely accepted as the primary cause of classical TN (cTN). Vascular compression involving the near half of the cisternal segment of trigeminal nerve was the most likely cause of patient's symptoms. And severe NVC was a strong imaging predictor of an optimal surgical outcome. Operative treatments for cTN include microvascular decompression (MVD) and various ablative procedures. However, a significant proportion of cTN patients with significant NVC fail to achieve long-term pain relief after technically successful surgery. Neuroimaging using magnetic resonance imaging (MRI) provides a noninvasive method to generate objective biomarkers of eventual response to TN surgery. This paper reviewed the progress of research on the prediction of surgical outcomes in TN with MRI.

Trigeminal neuropathic pain causes changes in affective processing of pain in rats

Trigeminal neuropathic pain has been modeled in rodents through the constriction of the infraorbital nerve (CCI-ION). Sensory alterations, including spontaneous pain, and thermal and mechanical hyperalgesia are well characterized, but there is a notable lack of evidence about the affective pain component in this model. Evaluation of the emotional component of pain in rats has been proposed as a way to optimize potential translational value of non-clinical studies. In rats, 22 and 50 kHz ultrasonic vocalizations (USVs) are considered well-established measures of negative and positive emotional states, respectively. Thus, this study tested the hypothesis that trigeminal neuropathic pain would result, in addition to the sensory alterations, in a decrease of 50 kHz USV, which may be related to altered function of brain areas involved in emotional pain processing. CCI-ION surgery was performed on 60-day-old male Wistar rats. 15 days after surgery, von Frey filaments were applied to detect mechanical hyperalgesia, and USV was recorded. At the same timepoint, systemic treatment with d,l-amphetamine (1 mg/kg) allowed investigation of the involvement of the dopaminergic system in USV emission. Finally, brain tissue was collected to assess the change in tyrosine hydroxylase (TH) expression in the nucleus accumbens (NAc) and c-Fos expression in brain areas involved in emotional pain processing, including the prefrontal cortex (PFC), amygdala, and NAc. The results showed that CCI-ION rats presented mechanical hyperalgesia and a significant reduction of environmental-induced 50 kHz USV. Amphetamine caused a marked increase in 50 kHz USV emission in CCI-ION rats. In addition, TH expression was lower in constricted animals and c-Fos analysis revealed an increase in neuronal activation. Taken together, these data indicate that CCI-ION causes a reduction in the emission of environmental-induced appetitive calls concomitantly with facial mechanical hyperalgesia and that both changes may be related to a reduction in the mesolimbic dopaminergic activity.

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

OBJECTIVE

Diffusion spectrum imaging (DSI) was used to quantitatively study the changes in the trigeminal cistern segment in patients with trigeminal neuralgia (TN) and to further explore the value of acquiring DSI data from patients with TN.

METHODS

To achieve high-resolution fiber tracking, 60 patients with TN and 35 healthy controls (HCs) were scanned with conventional magnetic resonance imaging (MRI) and DSI. The patients and the members of the control group were compared within and between groups. The correlations between quantitative parameters of DSI and the visual analog scale (VAS), and symptom duration and responsible vessel types were analyzed.

RESULTS

Compared with unaffected side of patients in the TN group, the affected side showed significantly decreased quantitative anisotropy (QA) (p < 0.001), fractional anisotropy (FA) (p = 0.001), and general FA (GFA) (p < 0.001). The unaffected side exhibited significantly decreased QA (p + 0.001), FA (p = 0.001), and GFA (p < 0.001) and significantly increased axial diffusivity (AD) (p = 0.036) compared with the affected side of patients in the TN group and the average values of HCs. There were significantly decreased QA (p = 0.046) and FA (p = 0.008) between the unaffected side of patients and the average values of HCs. GFA can evidently distinguish arteries, veins, and features of unaffected side in TN patients.

CONCLUSION

Using high-resolution fiber tracking technology, DSI can provide quantitative information that can be used to detect the integrity of trigeminal white matter in patients with TN and can improve the understanding of the disease mechanism.

Longitudinal alterations of the cisternal segment of trigeminal nerve and brain pain-matrix regions in patients with trigeminal neuralgia before and after treatment

Background

Trigeminal neuralgia (TN) is the most common type of chronic neuropathic facial pain, but the etiology and pathophysiological mechanisms after treatment are still not well understood. The purpose of this study was to investigate the longitudinal changes of the cisternal segment of the trigeminal nerve and brain pain-related regions in patients with TN before and after treatment using readout segmentation of long variable echo-train (RESOLVE) diffusion tensor imaging (DTI) and transverse relaxation (T2)-weighted sampling perfection with application-optimized contrast at different flip angle evolutions (T2-SPACE).

Methods

Twelve patients with TN and four healthy controls were enrolled in this study. All patients underwent assessment of the visual analog scale (VAS), and acquisition of RESOLVE DTI and T2-SPACE images before and at 1, 6, and 12 months after treatments. Regions-of-interest were placed on the bilateral anterior, middle, and posterior parts of the cisternal segment of the trigeminal nerve, the bilateral root entry zone (REZ), bilateral nuclear zone, and the center of pontocerebellar tracts, respectively. Voxel-based morphometry (VBM) analysis was conducted with T2-SPACE images, and gray matter volumes (GMV) were measured from brain pain-matrix regions.

Results

The results demonstrated that the VAS scores, the axial diffusivity of the middle part of the affected cisternal trigeminal nerve, the fractional anisotropy of the bilateral nuclear zones, and the mean diffusivity of the center of pontocerebellar tract significantly changed over time before and after treatment. The changes of GMV in the pain-matrix regions exhibited similar trends to the VAS before and after treatment.

Conclusion

We conclude that magnetic resonance imaging with RESOLVE DTI and VBM with T2-SPACE images were helpful in the understanding of the pathophysiological mechanisms in patients with TN before and after treatment.

Predictability of Fused 3D-T2-SPACE and 3D-TOF-MRA Images in Identifying Conflict in Trigeminal Neuralgia

Purpose

To evaluate the efficacy of fused three-dimensional T2 sampling perfection with application-optimized contrasts using different flip-angle evolutions (3D-SPACE) and three-dimensional time-of-flight magnetic resonance angiography (3D-TOF-MRA) sequences for detecting neurovascular compression (NVC) in patients presenting with trigeminal neuralgia (TN).

Methods

A prospective study was carried in 33 consecutive patients (m/f: 17/16; mean age, 56.3 ± 10.4 years) with unilateral TN confirmed NVC and consensus by two experienced radiologists on fused 3D-SPACE and 3D-TOF-MRA sequences of 3-tesla (3-T) MRI. All patients underwent microvascular decompression (MVD), using photos and video in surgery as documents compared with MRI. Both the MRI and MVD were reported for three grades (contact, compression, distortion), vessel types (artery or vein), identification of offending vessel, site (juxtapontine, cisternal, and juxtapetrous), and location (cranial, caudal, medial, lateral). Agreement between preoperative MRI visualization and surgical findings was assessed using the kappa (K) statistic.

Results

The k-values for the agreement were excellent for the grade of NVC (k=0.82), vessel types (k=0.78), and location of conflict (k=0.74), and good for identification of the offending vessel (0.65) and the site-affected vessel (k=0.69).

Conclusion

The fused D3-SPACE and 3D-TOF-MRA images are highly effective tools for the evaluation and treatment planning of NVC in TN patients.

Efficacy of medications in adult patients with trigeminal neuralgia compared to placebo intervention: a systematic review with meta-analyses

Background

Trigeminal neuralgia (TN) is characterized by brief, unilateral, sharp, stabbing, and shooting pain of the fifth cranial nerve. The objective of this systematic review with meta-analysis was to determine the effect of medications compared to placebo in adult patients with TN.

Methods

Review authors identified randomized placebo-controlled trials (RCTs) from PubMed, Web of Science, Cochrane, and EMBASE up to February 2021. We assessed the inclusion and exclusion criteria as well as the risk of bias of the studies based on the Cochrane Handbook. A total of 324 unduplicated references were scanned independently and reduced to eight relevant RCTs, with 89 patients included. Medications investigated included oral carbamazepine, subcutaneous sumatriptan, lidocaine (intranasal, 8% spray on the oral mucosa or intravenous), buprenorphine (ganglionic local opioid analgesia), and oral Nav1.7, a selective sodium channel blocker.

Results

Meta-analyses showed that overall patients receiving lidocaine reported a significantly lower post-treatment intensity of pain -3.8 points on a 0-10 scale (95% Cl = -4.653 to -2.873; P < 0.001). Patients who received lidocaine were 8.62 times more likely to have pain improvement than patients on placebo (P < 0.001). In one RCT, patients receiving oral carbamazepine showed a significant improvement in pain intensity of -32% compared to the placebo (P < 0.001). In one trial, patients receiving 3 mg subcutaneous sumatriptan had a significantly lower intensity of pain on average -6.1 points on a scale of 0-10 compared to placebo (P < 0.001) and a significant improvement in pain intensity of -75% compared to the improvement in the placebo group (P < 0.001). Patients who received subcutaneous sumatriptan were 10 times more likely to have pain improvement than those who received placebo (P = 0.001) in one study. Due to the unclear/high risk of bias and small sample size, the quality of the evidence for lidocaine in the treatment of TN was low.

Conclusion

Further studies are needed for carbamazepine, sumatriptan, buprenorphine, and oral Nav1.7 sodium channel blockers, as only one study reported outcomes.

Alterations of brain structural MRI are associated with outcome of surgical treatment in trigeminal neuralgia

BACKGROUND AND PURPOSE

To assess magnetic resonance imaging (MRI) alterations occurring in patients with trigeminal neuralgia (TN) and to explore the predictive ability of MRI for initial surgical outcome and long-term pain relief/recurrence after Gamma Knife radiosurgery (GKS).

METHODS

Thirty patients with idiopathic or classic TN, who underwent GKS and were followed for at least 24 months, were retrospectively included. Pre-treatment structural MRI and pre- and serial, postoperative clinical features were investigated. Fifteen age- and sex-matched healthy controls were also enrolled. Cortical thickness and gray matter (GM) volumes were assessed in TN patients relative to controls, as well as between patient subgroups according to treatment outcomes (initial responders/non-responders, patients with pain recurrence/long-lasting pain relief at the last follow-up). Clinical and MRI predictors of treatment outcomes were explored.

RESULTS

Cortical thinning of temporal, prefrontal, cingulate, somatosensory and occipital areas bilaterally was found in TN patients relative to controls. No cortical thickness and GM volume differences were observed when TN initial responders and non-responders were compared. Patients who experienced TN recurrence after initial pain relief were characterized by thicker parahippocampal and temporal cortices bilaterally and greater volume of right amygdala and hippocampus compared to patients with long-lasting pain relief. In TN patients, disease duration and baseline cortical thinning of right parahippocampal, left fusiform and middle temporal cortices were associated with poor outcome after GKS at the last follow-up (R² =0.57, p<0.001).

CONCLUSION

The study provides novel insights into structural brain alterations of TN patients, which might contribute to disease development and pain maintenance.

Comparison of first-time microvascular decompression with percutaneous surgery for trigeminal neuralgia: long-term outcomes and prognostic factors

Objective

Common surgical treatments for trigeminal neuralgia (TN) include microvascular decompression (MVD) and percutaneous procedures (glycerol rhizolysis; thermocoagulation; and balloon compression). Although the efficacy of each procedure has been documented, direct comparisons of their relative efficacies for TN are lacking. We aimed to directly compare long-term outcomes after first-time MVD with percutaneous surgery in primary (idiopathic and classical) TN and identify predictors of outcome.

Methods

We conducted a retrospective analysis of prospectively collected data on 185 patients undergoing MVD and 129 undergoing percutaneous surgery. Procedures were performed by one of two neurosurgeons in a single centre; an independent observer collected long-term follow-up data by interviews, using the same outcome measures for all procedures.

Results

MVD patients were younger than those undergoing percutaneous surgery (P <.001). MVD provided superior initial pain relief (P <.001): 87.0% had Barrow Neurological Institute class I or II pain scores after MVD compared with 67.2% after percutaneous surgery. The complication rate for percutaneous procedures was 35.7% and for MVDs was 24.9% (P =.04), including minor and transient complications. Kaplan-Meier analysis demonstrated that MVD provided longer pain relief than percutaneous procedures (P <.001); 25% of patients had recurrence at 96 months following MVD compared with 12 months after percutaneous surgery. Subgroup analysis showed that balloon compression provided more durable relief amongst percutaneous procedures. Multivariate analysis revealed that post-operative numbness and age were prognostic factors for percutaneous procedures (P =.03 and .01, respectively).

Conclusions

MVD provides better initial pain relief and longer durability of relief than percutaneous surgery, although carrying a small risk of major complications. Amongst percutaneous procedures, balloon compression gave the most durable relief from pain. Older age and post-operative numbness were predictors of good outcome from percutaneous surgery. These results can help clinicians to counsel patients with primary TN on neurosurgical treatment selection for pain relief.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-021-04793-4.

Recent Advances of Magnetic Resonance Neuroimaging in Trigeminal Neuralgia

Trigeminal neuralgia (TN) is a disease of unclear pathogenesis. It has a low incidence and is not fatal, but it can cause afflicted patients' depression or suicide. In the past, neurovascular compression was considered to be the main cause of TN, but recent studies have found that neurovascular contact is also common in asymptomatic patients and the asymptomatic side in symptomatic patients. This indicates that the neurovascular contact is not, or is only to a lesser extent, a factor in the development of TN. Thus, the study of the peripheral branches of the trigeminal nerve is necessary to understand the etiology of TN. With the development of imaging technology and the emergence of various imaging modalities, it is possible to study the etiology of TN and the pathological changes of related structures by magnetic resonance neuroimaging. This article reviews the recent advances in magnetic resonance neuroimaging of the trigeminal nerve.

Preoperative Decision-Making in Microvascular Decompression for Trigeminal Neuralgia: A Survey of Practicing Neurosurgeons

OBJECTIVE

Microvascular decompression (MVD) for trigeminal neuralgia (TN) results in durable pain freedom in a large percentage of appropriately selected patients. The decision to perform MVD is based on a combination of clinical symptomatic presentation and imaging findings demonstrating neurovascular compression (NVC) with surgeons weighting these variables differently. This study sought to determine the relative importance of clinical symptomatic presentation and imaging findings of NVC in decision-making to pursue MVD for TN among North American board-certified neurosurgeons.

METHODS

An online survey detailing the decision-making process involved in the workup and treatment of TN with MVD was distributed to all American Association of Neurological Surgeons registered board-certified neurosurgeons in North America.

RESULTS

From 3010 functional email addresses, there were 309 responses to the survey (10% response rate). The majority of respondents (76%) reported only operating on patients with classic type 1 TN (T1TN) while only 32% chose to operate on patients with imaging findings of vascular compression in the absence of T1TN symptoms. In contrast to low-volume surgeons, high-volume surgeons weighed imaging evidence of vascular compression more heavily into the decision-making process to operate.

CONCLUSIONS

The majority of responding neurosurgeons weigh symptomatic presentation more heavily than imaging evidence of NVC when deciding on whom to perform MVD. High-volume surgeons tend to be more attentive to NVC in their decision-making to perform MVD when compared with low-volume surgeons.

Trigeminal neuralgia: An overview from pathophysiology to pharmacological treatments

The trigeminal nerve (V) is the fifth and largest of all cranial nerves, and it is responsible for detecting sensory stimuli that arise from the craniofacial area. The nerve is divided into three branches: ophthalmic (V1), maxillary (V2), and mandibular (V3); their cell bodies are located in the trigeminal ganglia and they make connections with second-order neurons in the trigeminal brainstem sensory nuclear complex. Ascending projections via the trigeminothalamic tract transmit information to the thalamus and other brain regions responsible for interpreting sensory information. One of the most common forms of craniofacial pain is trigeminal neuralgia. Trigeminal neuralgia is characterized by sudden, brief, and excruciating facial pain attacks in one or more of the V branches, leading to a severe reduction in the quality of life of affected patients. Trigeminal neuralgia etiology can be classified into idiopathic, classic, and secondary. Classic trigeminal neuralgia is associated with neurovascular compression in the trigeminal root entry zone, which can lead to demyelination and a dysregulation of voltage-gated sodium channel expression in the membrane. These alterations may be responsible for pain attacks in trigeminal neuralgia patients. The antiepileptic drugs carbamazepine and oxcarbazepine are the first-line pharmacological treatment for trigeminal neuralgia. Their mechanism of action is a modulation of voltage-gated sodium channels, leading to a decrease in neuronal activity. Although carbamazepine and oxcarbazepine are the first-line treatment, other drugs may be useful for pain control in trigeminal neuralgia. Among them, the anticonvulsants gabapentin, pregabalin, lamotrigine and phenytoin, baclofen, and botulinum toxin type A can be coadministered with carbamazepine or oxcarbazepine for a synergistic approach. New pharmacological alternatives are being explored such as the active metabolite of oxcarbazepine, eslicarbazepine, and the new Nav1.7 blocker vixotrigine. The pharmacological profiles of these drugs are addressed in this review.

Molecular mechanisms of trigeminal neuralgia: A systematic review

OBJECTIVE

To conduct a systematic review of the available literature for primary research articles identifying potential gene mutations, polymorphisms and other molecular regulatory mechanisms related to trigeminal neuralgia in order to identify the genetic and molecular models of primary trigeminal neuralgia currently being investigated.

METHODS

PubMed and Web of Science were systematically searched to identify primary research articles discussing genetic predictors of trigeminal neuralgia and neuropathic pain that were published prior to July 2020. This review was conducted according to PRISMA guidelines.

RESULTS

Out of the 333 articles originally identified, a total of 14 papers were selected for study inclusion. These articles included 5 human studies, 6 mouse studies and 3 rat studies. Four articles investigated sodium channels, 1 investigated a sodium channel and nerve growth factor receptor, 2 investigated potassium channels, 1 investigated calcium channels, 1 investigated the downstream regulatory element antagonist modulator protein, 1 investigated the dynorphin-kappa opioid receptor system, 1 investigated TRPA1, 1 investigated the Nrg1/ErbB3/ErbB2 signaling complex, 1 investigated a serotonin transporter and 1 investigated potassium channels, sodium channels, calcium channels, chloride channels, TRP channels and gap junctions.

CONCLUSION

Researchers have identified multiple genetic and molecular targets involved with potential pathophysiologies that have a relationship to the creation of trigeminal neuralgia. At this time, there does not seem to be clear causal frontrunner, demonstrating the possibility that genetic predisposition to trigeminal neuralgia may involve multiple genes and/or downstream products, such as ion channels.

The Use of MRI in Preoperative Decision-Making for Trigeminal Neuralgia: A Single-Center Study

OBJECTIVE

Few studies have examined associations between vascular compression and postoperative pain relief in patients undergoing microvascular decompression (MVD) for treatment of medically refractory type 1 trigeminal neuralgia (TN). The authors sought to examine for associations between vascular compression and postoperative pain relief to determine the utility of preoperative magnetic resonance imaging (MRI) in surgical decision-making for TN.

METHODS

The charts of 59 patients who underwent 60 MVDs for TN between 2007 and 2017 at a single academic institution were reviewed. Patient demographics, the presence of compressing vessel on preoperative MRI and intraoperatively, complications, follow-up time, performance of a partial sensory rhizotomy, and pain resolution at most recent follow-up were recorded. Sensitivity and specificity of MRI for detecting vascular compression were calculated and associations between preoperative and intraoperative evidence of vascular compression with postoperative pain relief were examined.

RESULTS

Sensitivity and specificity of preoperative MRI determined through blinded reads by the senior author were 65.3% (95% confidence interval, 13.5-32.0) and 90.9% (95% confidence interval, 86.1-100.0), respectively. Overall, 76.3% of patients were pain free at most recent follow-up. Preoperative MRI and intraoperative evidence of vascular compression were not associated with postoperative pain relief at most recent follow-up (P = 0.47 and 0.43, respectively).

CONCLUSIONS

The findings of lower sensitivity and poor interrater reliability of MRI, as well as a lack of association between compressive vessel and postoperative pain relief reported in this study, suggest the decision to pursue MVD for TN should be based more heavily on classic symptomatic presentation over preoperative evidence of vascular compression.

Advances in diagnosis, classification, pathophysiology, and management of trigeminal neuralgia

Trigeminal neuralgia is a very painful neurological condition with severe, stimulus-evoked, short-lasting stabbing pain attacks in the face. The past decade has offered new insights into trigeminal neuralgia symptomatology, pathophysiology, and treatment, leading to a change in the classification of the condition. An accurate diagnosis is crucial because neuroimaging interpretation and clinical management differ among the various forms of facial pain. MRI using specific sequences should be a part of the diagnostic workup to detect a possible neurovascular contact and exclude secondary causes. Demonstration of a neurovascular contact should not be used to confirm a diagnosis but rather to facilitate surgical decision making. Carbamazepine and oxcarbazepine are drugs of first choice for long-term treatment, whereas microvascular decompression is the first-line surgery in medically refractory patients. Advances in neuroimaging techniques and animal models will provide further insight into the causes of trigeminal neuralgia and its pathophysiology. Development of more efficacious treatment options is highly warranted.

Increased CSF Levels of Apolipoproteins and Complement Factors in Trigeminal Neuralgia Patients-In Depth Proteomic Analysis Using Mass Spectrometry

The main cause of trigeminal neuralgia (TN) is compression of a blood vessel at the root entry zone of the trigeminal nerve. However, a neurovascular conflict does not seem to be the only etiology and other mechanisms are implicated in the development of the disease. We hypothesized that TN patients may have distinct protein expression in the CSF. In this study, lumbar CSF from TN patients (n = 17), scheduled to undergo microvascular decompression, and from controls (n = 20) was analyzed and compared with in depth mass spectrometry TMTbased quantitative proteomics. We identified 2552 unique proteins, of which 46 were significantly altered (26 increased, and 20 decreased, q-value < .05) in TN patients compared with controls. An over-representation analysis showed proteins involved in high-density lipoprotein, such as Apolipoprotein A4, Apolipoprotein M, and Apolipoprotein A1, and the extracellular region, including proteins involved in the complement cascade to be over-represented. We conclude that TN patients have distinct protein expression in the CSF compared to controls. The pathophysiological background of the protein alterations found in this study warrants further investigation in future studies. PERSPECTIVE: In this article, cerebrospinal fluid from patients with trigeminal neuralgia was analyzed using in depth shotgun proteomics, revealing 46 differentially expressed proteins compared to controls. Among these, apolipoproteins and proteins involved in the complement system were elevated and significantly over-represented, implying an inflammatory component in the pathophysiology of the disease.

Diffusivity parameters of diffusion tensor imaging and apparent diffusion coefficient as imaging markers for predicting the treatment response of patients with trigeminal neuralgia

OBJECTIVE

Trigeminal neuralgia (TN) is facial pain that is usually caused by neurovascular compression syndrome and is characterized by suddenly intense and paroxysmal pain. Radiofrequency lesioning (RFL) is one of the major treatments for TN, but the treatment response for RFL is sometimes inconsistent, and the recurrence of TN is not uncommon. This study aimed to estimate the outcome predictors of TN treated with RFL by using the parameters of diffusion tensor imaging (DTI).

METHODS

Fifty-one patients with TN who were treated with RFL were enrolled in the study. MRI was performed in all patients within 1 week before surgery. The visual analog scale was used to evaluate symptom severity at three time points: before, 1 week after, and 3 months after RFL. The involved cisternal segment of the trigeminal nerves was manually selected, and the histograms of each of the diffusivity metrics-including the apparent diffusion coefficient (ADC), fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD)-were measured. The differences in the means, as well as the kurtosis and skewness of each of the diffusivity metrics between the nonrecurrent and recurrent groups, were then analyzed using the Mann-Whitney U-test.

RESULTS

There were significantly lower kurtosis values (a broader peak of the distributional curves) for both FA and ADC in the recurrent group (p = 0.0004 and 0.015, respectively), compared to the nonrecurrent group. The kurtoses of AD and RD, as well as the mean and skewness of all other diffusivity metrics, did not show significant differences between the two groups.

CONCLUSIONS

The pretreatment diffusivity metrics of DTI and ADC may be feasible imaging biomarkers for predicting the outcome of TN after RFL. A clarification of the kurtosis value of FA and ADC is helpful for determining the prognosis of patients after RFL.

Imaging vs quantitative sensory testing to predict chronic pain treatment outcomes

In this article, I review the concept of personalized pain management and consider how brain imaging and quantitative sensory testing can be used to derive biomarkers of chronic pain treatment outcome. I review how different modalities of brain imaging can be used to acquire information about brain structure and function and how this information can be linked to individual measures of pain.

Biomarkers in Temporomandibular Disorder and Trigeminal Neuralgia: A Conceptual Framework for Understanding Chronic Pain

In this review, we will explore the use of biomarkers in chronic pain, using the examples of two prototypical facial pain conditions: trigeminal neuralgia and temporomandibular disorder. We will discuss the main categories of biomarkers and identify various genetic/genomic, molecular, neuroradiological, and psychophysical biomarkers in both facial pain conditions, using them to compare and contrast features of neuropathic, nonneuropathic, and mixed pain. By using two distinct model facial pain conditions to explore pain biomarkers, we aim to familiarize readers with different types of biomarkers currently being studied in chronic pain and explore how these biomarkers may be used to develop new precision medicine approaches to pain diagnosis, prognosis, and management.

Trigeminal Nerve Compression Without Trigeminal Neuralgia: Intraoperative vs Imaging Evidence

BACKGROUND

While high-resolution imaging is increasingly used in guiding decisions about surgical interventions for the treatment of trigeminal neuralgia, direct assessment of the extent of vascular contact of the trigeminal nerve is still considered the gold standard for the determination of whether nerve decompression is warranted.

OBJECTIVE

To compare intraoperative and magnetic resonance imaging (MRI) findings of the prevalence and severity of vascular compression of the trigeminal nerve in patients without classical trigeminal neuralgia.

METHODS

We prospectively recruited 27 patients without facial pain who were undergoing microvascular decompression for hemifacial spasm and had undergone high-resolution preoperative MRI. Neurovascular contact/compression (NVC/C) by artery or vein was assessed both intraoperatively and by MRI, and was stratified into 3 types: simple contact, compression (indentation of the surface of the nerve), and deformity (deviation or distortion of the nerve).

RESULTS

Intraoperative evidence of NVC/C was detected in 23 patients. MRI evidence of NVC/C was detected in 18 patients, all of whom had intraoperative evidence of NVC/C. Thus, there were 5, or 28% more patients in whom NVC/C was detected intraoperatively than with MRI (Kappa = 0.52); contact was observed in 4 of these patients and compression in 1 patient. In patients where NVC/C was observed by both methods, there was agreement regarding the severity of contact/compression in 83% (15/18) of patients (Kappa = 0.47). No patients exhibited deformity of the nerve by imaging or intraoperatively.

CONCLUSION

There was moderate agreement between imaging and operative findings with respect to both the presence and severity of NVC/C.

Correlations between the trigeminal nerve microstructural changes and the trigeminal-pontine angle features

BACKGROUND

Morphological and microstructural changes of the trigeminal nerve due to neurovascular compression (NVC) have been reported in primary trigeminal neuralgia (PTN) patients. This investigation was to examine the relationship between the trigeminal-pontine angle and nerve microstructural changes.

METHODS

Twenty-five patients underwent microvascular decompression (MVD) for trigeminal neuralgia, and 25 age- and sex-matched controls were studied. The two groups underwent high-resolution three-dimensional MRI and diffusion tensor imaging (DTI). Bilateral trigeminal-pontine angle, cross-sectional area of cerebellopontine angle (CPA) cistern, and the length of trigeminal nerve were evaluated. The mean values of fractional anisotropy and apparent diffusion coefficient at the site of NVC were also measured. Correlation analyses were performed for the trigeminal-pontine angle and the diffusion metrics (FA and ADC) in PTN patients.

RESULTS

The mean trigeminal-pontine angle and FA value on the affected side was significantly smaller than the unaffected side and the control group (p < 0.001), while the mean ADC value was significantly increased (p < 0.01). When taking the conflicting vessel types into consideration, the angle affected by the superior cerebellar artery (SCA) was statistically sharper than when affected by other vessels (p < 0.01). However, there were no significant changes in the area of the CPA cistern or the length of the trigeminal nerve between the groups. Correlation analyses showed that the trigeminal-pontine angle was positively correlated with FA and negatively correlated with ADC.

CONCLUSIONS

A sharp trigeminal-pontine angle may increase the chance of NVC and exacerbate nerve degeneration, which may be one of the supplementary factors that contribute to the pathogenesis of trigeminal neuralgia.

The Value of Three-Dimensional Brain Volume Combined with Time-of-Flight MRA in Microvascular Decompression

OBJECTIVES

To explore the guidance value of preoperative 3-dimensional brain volume (3D-BRAVO) and 3-dimensional time-of-flight (3D-TOF) MRA scanning for microvascular decompression.

METHODS

One hundred thirteen patients treated with microvascular decompression from February 2016 to February 2018 in the First Affiliated Hospital of Dalian Medical University were retrospectively analyzed. All patients received 3D-BRAVO combined with 3D-TOF MRA sequence reconstruction before the operation. The anatomical relationship of neurovascular tissues was analyzed and compared with the results of intraoperative exploration.

RESULTS

The results of MVD showed that the number of positive cases was 108 (95.6%) on the diseased side. 3D-BRAVO combined with 3D-TOF sequence reconstruction resulted in 106 positive cases (93.8%), with a 98.1% positive coincidence rate and a 13.2% false positive rate (p < 0.05). 3D-BRAVO-TOF sequence reconstruction of trigeminal neuralgia showed a positive coincidence in 78 cases (92.8%) and for hemifacial spasm a positive coincidence was found in 27 cases (93.1%).

CONCLUSION

3D-BRAVO combined with 3D-TOF sequence reconstruction before microvascular decompression can fully evaluate the morphology, location, and anatomical relationship of lesions, which is of guidance value for clinical diagnosis and treatment.

Diffusion tensor imaging of microstructural alterations in the trigeminal nerve due to neurovascular contact/compression

BACKGROUND

Several recent studies have focused on microstructural changes in the trigeminal nerve in trigeminal neuralgia using diffusion tensor imaging (DTI). However, alterations after microvascular decompression (MVD) have rarely been investigated. Furthermore, the trigeminal nerve of asymptomatic individuals also presenting with neurovascular contact/compression (NVC) has not yet been studied.

METHODS

Thirty-four patients suffering from trigeminal neuralgia and 34 healthy age-matched controls, who were identified as having unilateral NVC signs, underwent both DTI and high-resolution magnetic resonance imaging (MRI) for comparison. All trigeminal neuralgia patients underwent a post-surgical MRI scan after 7 days and a follow-up MRI scan within 6-8 months after surgery. The apparent diffusion coefficients (ADCs) and fractional anisotropy (FA) values were measured from coronal images in which the nerves from the root exit point to the distal segment were clearly shown.

RESULTS

In 34 trigeminal neuralgia patients, the absolute FA value was significantly lower on the affected side (mean FA, 0.34 ± 0.03) than on the unaffected side (mean FA, 0.37 ± 0.05, p < 0.001). The FA ratio was also significantly different between the trigeminal neuralgia group (Rs_FA, 0.92 ± 0.06) and the control group (Rs_FA, 0.99 ± 0.09) (p = 0.001). The absolute ADC value between the two sides in patients and the ratios of ADC between the trigeminal neuralgia and control groups did not show any significant differences (p = 0.21 and 0.29, respectively). However, in 34 healthy subjects presenting with signs of NVC, neither the FA value nor the ADC showed a difference between sides (p > 0.05). The FA ratio of patients showed a significant increase on two follow-up MRI scans compared to the preoperative FA (p = 0.02 and 0.002, respectively), while the ADC ratio showed a significant decrease at 6 months after MVD (p = 0.004).

CONCLUSION

This study of trigeminal neuralgia due to NVC found that DTI indexes could reflect alterations in the affected trigeminal nerve. Furthermore, a reversible change after MVD surgery could be potentially valuable for monitoring the change in white matter of the trigeminal nerve.

Hemodynamic features of offending vessels at neurovascular contact in patients with trigeminal neuralgia and hemifacial spasm

OBJECTIVE

Offending vessels at the site of neurovascular contact (NVC) in patients with trigeminal neuralgia (TN) and hemifacial spasm (HFS) may have specific hemodynamic features. The purpose of this study was to investigate the wall shear stress (WSS) of offending vessels at NVCs by conducting a computational fluid dynamics (CFD) analysis.

METHODS

The authors retrospectively analyzed the cases of 20 patients (10 with TN and 10 with HFS) evaluated by 3D CT angiography and used the imaging findings for analysis of the hemodynamic parameters. The 3D CFD images were directly compared with the NVCs determined by simulated multifusion images of CT angiogram and MR cisternogram, and operative photos. The magnitudes of the WSS (WSSm) at the proximal (WSSm-p), just-beginning (WSSm-j), contact site (WSSm-s), and distal (WSSm-d) areas of each NVC were analyzed. The ratios of the WSSm-j, WSSm-s, and WSSm-d areas to the WSSm-p area were calculated individually. The direction of the WSS (WSSv) and its temporal variation (WSSvV) were depicted and morphologically compared with the NVC confirmed by simulated images and operative findings.

RESULTS

The ratios of WSSm at the just-beginning and the contact site to the proximal area of the NVCs (WSSm-j/WSSm-p and WSSm-s/WSSm-p) were both significantly higher than that at the distal area (WSSm-d/WSSm-p) (p < 0.05). The WSSv and WSSvV at the NVCs showed small variation in a single cardiac cycle, especially along the areas that were in contact with the affected nerve.

CONCLUSIONS

Areas of relatively high WSSm and temporal variation of WSSm (WSSmV) were observed at the NVCs. Less mobility of the WSSv and WSSvV was detected along the side of the vessels in contact with the nerves. These findings may be consistent with the actual area of the NVC. Hemodynamic features of the site of NVC can be added to the preoperative simulation for MVD surgery, which may be useful for the diagnosis and treatment planning of TN and HFS.

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

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.

Vascular Offenders in Trigeminal Neuralgia: A Unified Classification and Assessment of the Outcome of Microvascular Decompression

BACKGROUND

Vascular loop compression remains the most accepted theory for trigeminal neuralgia (TN). Apart from the normal adjoining vascular loops, certain unusual vascular loops incriminated in TN such as vertebrobasilar dolichoectasia and pure venous compressions do not truly fit into the traditional classification. Moreover, vascular diseases such as cavernoma and aneurysms causing TN are considered as secondary TNs. There is a lack of unified classification for TN with underlying vascular offenders, otherwise amenable to microvascular decompression.

METHODS

We classified vascular offenders in TN (n = 53) into the usual offenders such as superior cerebellar artery or anterior inferior cerebellar artery loop with (n = 4) or without (n = 34) superior petrosal vein loop (n = 38, group I). The unusual vascular offenders (n = 15, group II) comprised unusual arterial loops (n = 4, IIa), pure venous compressions (n = 8, IIb) and vascular diseases (n = 3, IIc). The clinical symptoms, pain severity scores, and surgical outcomes were compared.

RESULTS

A right-sided preference and male predominance typified the unusual group. The incidence of atypical pain and sensory impairment was higher in group II. Group II also showed a less favorable immediate pain outcome, particularly the patients in group IIb. Group IIb also showed a higher incidence of postoperative hemorrhagic complications. However, long-term outcomes did not differ significantly.

CONCLUSIONS

Unusual vascular offenders in TN do constitute a significant population. They differ from the usual group with respect to the type of pain, gender, and side of involvement and tend to have more complications with similar pain outcomes after microvascular decompression.

The Tethered Effect of Vestibular Schwannoma Tumor Shrinkage Following Stereotactic Radiosurgery in Secondary Trigeminal Neuralgia

BACKGROUND

Compression of the trigeminal nerve by vessels and tumors causes trigeminal neuralgia. However, a tethering effect, provoking an abnormal root-stretching force, has been previously reported to play a role in trigeminal nerve hyperexcitability. We report 2 patients with vestibular schwannomas treated by stereotactic radiosurgery (SRS) who presented with typical manifestations of trigeminal neuralgia after tumor shrinkage. Furthermore, we discuss the mechanisms of trigeminal neuralgia.

CASE DESCRIPTION

Two patients without a history of trigeminal dysfunction, including trigeminal neuralgia, underwent SRS for vestibular schwannomas. Both patients demonstrated tumor shrinkage after transient tumor expansion following SRS. Neither patient presented with facial pain or dysesthesia at the time of peak tumor volume. However, trigeminal neuralgia occurred after tumor shrinkage. One patient underwent surgery, as the neuralgia was refractory to medical treatment; although the trigeminal nerve was adhered and tethered to the tumor, no neurovascular conflict was identified between the tumor and the nerve. We removed the tumor partially, dissecting between the nerve and the tumor, and relieved the tethered effect. Trigeminal neuralgia was relieved without medication after surgery.

CONCLUSIONS

The present cases demonstrate a tethered effect of tumor shrinkage after SRS, which was considered to play a role in trigeminal neuralgia. Surgical dissection surrounding the nerve root is effective for medically resistant neuralgia, even if the tumor shrinks. Partial tumor removal is adequate in such cases, as the tumor has been controlled by radiosurgery.

Volume Gain of Brainstem on Medication-Overuse Headache Using Voxel-Based Morphometry

Background:

Histopathology identified the anatomical and molecular abnormalities of brainstem nuclei in migraine patients. However, the exact whole brainstem structural changes in vivo have not yet been identified in medication-overuse headache (MOH) transformed from migraine. The aim of this study was to investigate the regional volume changes over the whole brainstem in the MOH patients using voxel-based morphometry (VBM) in vivo.

Methods:

High-resolution three-dimensional structural images were obtained using a 3.0-Tesla magnetic resonance system from 36 MOH patients and 32 normal controls (NCs) who were consecutively recruited from the International Headache Center, Chinese People's Liberation Army General Hospital, from March 2013 to June 2016. VBM was used to assess the brainstem structural alteration in the MOH patients, and voxel-wise correlation was performed to evaluate the relationship with the clinical characteristics.

Results:

The brainstem region with increased volume located in the left ventrolateral periaqueductal gray (MNI coordinate: -1, -33, -8), ventral tegmental area (MNI coordinate: 0, -22, -12), bilateral substantia nigra (MNI coordinate: -8, -16, -12, 9, -16, -12), and trigeminal root entry zone (MNI coordinate: -19, -29, -31; 19, -32, -29) in MOH patients compared with NCs. The headache visual analog scale score was positively related with the left rostral ventromedial medulla (RVM) (MNI coordinate: -1, -37, -56; cluster size: 20; r = 0.602) in the MOH patients.

Conclusions:

The regional volume gain of brainstem could underlie the neuromechanism of impaired ascending and descending pathway in the MOH patients, and the left RVM volume alteration could imply the impaired tolerance of nociceptive pain input and could be used to assess the headache disability in the MOH patients.

Mapping fine-scale anatomy of gray matter, white matter, and trigeminal-root region applying spherical deconvolution to high-resolution 7-T diffusion MRI

OBJECTIVES

We assessed the use of high-resolution ultra-high-field diffusion magnetic resonance imaging (dMRI) to determine neuronal fiber orientation density functions (fODFs) throughout the human brain, including gray matter (GM), white matter (WM), and small intertwined structures in the cerebellopontine region.

MATERIALS AND METHODS

We acquired 7-T whole-brain dMRI data of 23 volunteers with 1.4-mm isotropic resolution; fODFs were estimated using constrained spherical deconvolution.

RESULTS

High-resolution fODFs enabled a detailed view of the intravoxel distributions of fiber populations in the whole brain. In the brainstem region, the fODF of the extra- and intrapontine parts of the trigeminus could be resolved. Intrapontine trigeminal fiber populations were crossed in a network-like fashion by fiber populations of the surrounding cerebellopontine tracts. In cortical GM, additional evidence was found that in parts of primary somatosensory cortex, fODFs seem to be oriented less perpendicular to the cortical surface than in GM of motor, premotor, and secondary somatosensory cortices.

CONCLUSION

With 7-T MRI being introduced into clinical routine, high-resolution dMRI and derived measures such as fODFs can serve to characterize fine-scale anatomic structures as a prerequisite to detecting pathologies in GM and small or intertwined WM tracts.

Reliability of MRI for predicting characteristics of neurovascular conflicts in trigeminal neuralgia: implications for surgical decision making

OBJECTIVE

The choice of microvascular decompression (MVD), among the several other surgical options, for treating refractory classical trigeminal neuralgia (TN) relies mostly on preoperative imaging, but the degree of reliability of MRI remains a matter of debate. The authors approached the question of predictability of neurovascular conflict (NVC) in a series of 100 protocolized MRI studies from patients with TN who underwent MVD, by reexamination of MR images, blinded to the clinical data and surgical findings, including the side of the neuralgia.

METHODS

Patients included in the study were those who underwent MVD after surgical indication had been determined based on a protocolized imagery workup (3D high-resolution T2-weighted cisternography centered on the trigeminal nerve, 3D time-of-flight angiography, and 3D gadolinium-enhanced T1-weighted imaging) performed at our institution. All MR images were blindly reexamined, and neurovascular relationships were described on both sides, noting the existence of compression, vessels involved, situation along the root, and degree of compression. The results of MRI evaluation were then compared with actual surgical findings. The extent of agreement and quality of the prediction were expressed with Cohen's kappa coefficient (κ) and receiver operating characteristic (ROC) statistics.

RESULTS

A conflict had actually been found during surgery in 94 of 100 patients. The sensitivity of MRI to detect a conflict was 97% and the specificity was 50%. Vessel type was identified with high reliability (κ = 0.80), while the grade of the conflict and its situation along the root showed poor to average reliability (κ = 0.38 and κ = 0.40, respectively). The area under the ROC curve for predicting the presence of a conflict according to the grades of conflict seen on MRI was 0.93, which is considered very good. The positive predictive value was differentiated according to the grade of conflict, with a very high value for high grades of vascular conflict.

CONCLUSIONS

This study shows an overall good reliability of MRI to predict the existence of an NVC. The prediction value is excellent for high grades of compression. Some apparent low-grade compressions on MRI may be revealed as false positives in surgical exploration. This raises the question of what other imaging methods might be used to determine not only the existence of a conflict but also its degree of compression. The degree of compression is of paramount importance to predict the probability of long-term pain relief, and therefore in the decision to propose MVD as the first choice of surgical treatment.

Diffusion Tensor Imaging of Axonal and Myelin Changes in Classical Trigeminal Neuralgia

OBJECTIVE

Trigeminal neuralgia (TN) is commonly associated with pathologic factors of axonopathy and demyelination resulting from neurovascular compression at the trigeminal root entry zone (REZ). Decompression surgery can relieve TN pain, likely by resolving such structural abnormalities. To test this hypothesis, we used diffusion tensor imaging (DTI) to capture the full extent of trigeminal microarchitecture changes in vivo in patients with TN.

METHODS

Twenty-four patients with TN were compared with 28 controls. DTI metrics of fractional anisotropy (FA) and mean, parallel, and perpendicular diffusivities (MD, λ_||, and λ_⊥, respectively) were calculated in isolation at each trigeminal REZ. In 6 patients with pain relief following decompression surgery, repeated studies were performed 2 times (1 week and 4-6 months) after surgery to detect dynamic changes in FA, MD, λ_||, and λ_⊥.

RESULTS

We observed significant FA reductions and increased diffusivity at the affected trigeminal REZ, corresponding to known underlying pathologic changes, including axonal edema and demyelination. Specifically, our results showed that these DTI-derived metrics are discriminating features for patients with TN according to the support vector machine approach. After effective treatment, diffusion recovery at 1 week was mainly due to the decrease in λ_|| (consistent with axonal membrane stabilization), whereas at 4-6 months it was due to the predominant reduction in λ_⊥ (consistent with remyelination).

CONCLUSIONS

Together, these results support that DTI permits the noninvasive detection of the trigeminal microstructural abnormalities underlying TN in vivo, and DTI-derived metrics could be considered surrogate markers of the axonal and myelin states for monitoring patients.