| BackgroundTrigeminal neuralgia(TN)is a common neurogenic pain disorder characterized by severe,paroxysmal,electric shock-like or stabbing pain in the distribution of the trigeminal nerve on one side of the face.The intense pain significantly impacts the quality of life of affected individuals.Primary trigeminal neuralgia(PTN)can be divided into typical trigeminal neuralgia(CTN)and idiopathic trigeminal neuralgia(ITN).according to the definition of the third Edition of the International Classification of Headache,Classical trigeminal neuralgia(CTN)is trigeminal neuralgia caused by neurovascular compression(NVC).Idiopathic trigeminal neuralgia(ITN)hasn’t a known cause,including NVC.The surgical procedures used for the two types of pain are also different.Microvascular decompression(MVD)is a surgical procedure used to treat CTN by removing the blood vessels that compress the trigeminal nerve,allowing for nerve reconstruction.It is currently the most effective way to cure CTN.In contrast,ITN is typically treated with internal neurolysis(IN)which involves the longitudinal dissection of the intracranial nerve roots to achieve micro-nerve destruction.Although both CTN and ITN belong to primary trigeminal neuralgia,which is a peripheral chronic pain,their pathophysiological basis and pathogenesis are different.It is generally believed that the pathophysiological basis of CTN is related to the compression of the trigeminal nerve in the intracranial segment by blood vessels,leading to secondary demyelination of the nerve.The peripheral pathogenesis includes the "ignition" theory,"short circuit" theory and "sympathetic excitation" theory,etc.,In contrast,the pathophysiological basis and pathogenesis of ITN are still not fully clear.However,studies have shown that ITN may be associated with central sensitization of neuropathic pain,which can exacerbate and prolong neuropathic pain.In addition,research has also suggested a relationship between ITN and inflammatory responses in the trigeminal ganglion.Current research has demonstrated that the onset of CTN is closely related to abnormalities in brain structure and function,and there may be extensive changes in brain network structure.However,unlike CTN,there have been no studies investigating the functional connectivity abnormalities in the brains of ITN patients,nor have there been studies exploring the differences between CTN and ITN.Furthermore,the relationship between clinical symptom improvement and changes in brain functional network connectivity after surgical intervention remains unclear for both CTN and ITN patients.The resting-state functional magnetic resonance imaging studies of CTN and ITN provide neuroimaging evidence for revealing the functional and structural characteristics of the neural networks associated with these two neurological disorders.Resting-state functional network graph theory methods can analyze the topology and characteristics of the brain’s neural network,and reveal the function and dynamic changes of the neural network by measuring different network indicators such as node degree centrality and small-worldness,thereby enhancing understanding of brain function and its abnormalities,and achieving the goal of brain function research.Graph theory-based Degree centrality(DC)is a measurement method that calculates the number of edges connected between a node and other nodes.The greater the degree of a node,the higher its centrality in the network,indicating its importance.Betweenness centrality(BC)is another important concept in graph theory,which calculates the ratio between the number of shortest paths passing through a node and the total number of shortest paths between two nodes in a network.If a node connects many other nodes in the network,its betweenness centrality will be higher,indicating that it has a more important position and role in the network.ObjectiveBased on resting state functional magnetic resonance(fMRI),this study used graph theory analysis to explore the differences in the topological properties of the brain functional networks of CTN and ITN patients,observe and evaluate the level of information transmission and processing of the brain networks of CTN and ITN and their changes before and after surgical intervention,and help to understand the degree of influence of two different types of trigeminal neuralgia on pain centers.In order to further understand the neurophysiological mechanism of CTN and ITN,neuroimaging evidence at the network level is provided.MethodsThis study recruited 26 patients with CTN and 10 patients with ITN from the First Affiliated Hospital of the University of Science and Technology of China(Anhui Provincial Hospital)and matched them according to age and gender.magnetic resonance imaging(MRI)data,including 3D T1 structural images and resting state data,were collected for all patients before and after surgery.After that,the whole brain was divided into 90 brain regions according to the AAL template,and the average temporal activation levels of all voxels in each brain region were extracted to construct pair-to-pair correlation maps of the 90 brain regions,and then the topological characteristics of each brain region for each patient were analyzed,including degree centrality and intermediate centrality.Then,we compared the differences in the preoperative topological structure characteristics of the CTN and ITN groups,as well as the changes in resting-state topological characteristics before and after surgery between the CTN and the ITN group.Results1.A total of 36 TN patients,including 26 CTN patients and 10 ITN patients were enrolled.There were no significant differences in age,gender and course of disease between the two groups(P>0.05).There was no significant difference in preoperative pain scores between the two groups(P>0.05),however postoperative pain scores in each group were significantly decreased compared with preoperative pain scores(P<0.001).2.Degree centrality(DC):CTN group was significantly lower than ITN group in right middle orbitofrontal gyrus(P<0.005),right parahippocampal gyrus(P<0.005)and right cerebellum(P<0.05).What we found interesting was that the brain regions with preoperative and postoperative degree of central change in each group were exactly the brain regions with preoperative differences between the two groups.In CTN group,degree centrality had an increase after right middle orbitofrontal gyrus operation(P<0.05).In ITN group,degree centrality showed a decrease in right parahippocampal gyrus and right cerebellum after operation(P<0.05).3.Betweenness centrality(BC):The betweenness centrality(BC)in the right parahippocampal gyrus was significantly lower in the CTN group compared to the ITN group(P<0.005).Conclusion1.The brain regions with shared degree centrality and betweenness centrality between ITN and CTN are the right middle orbitofrontal gyrus,right parahippocampal gyrus,and right cerebellum.This suggests that these regions may be common painrelated brain areas in both types of trigeminal neuralgia.2.In the intergroup comparison before surgery,the DC values in three brain regions were significantly higher in the ITN group than in the CTN group,indicating significant differences between the two types of pain in terms of their impact on brain connectivity.In these regions,ITN exhibited higher centrality and/or functional connectivity than CTN.3.Although the right middle orbitofrontal gyrus,parahippocampal gyrus,and cerebellum are common brain regions for both CTN and ITN,the BC value in the right parahippocampal gyrus was significantly higher in the ITN group than in the CTN group.This indicates that in these three common brain regions,the parahippocampal gyrus node is more important in the ITN pain network,which may be related to its neural activity and transmission of information.4.Both CTN and ITN patients achieved satisfactory results after surgery,which involved microvascular decompression and nerve combing,respectively.The brain regions with topological changes after surgery were exactly the differential brain regions between the two types of trigeminal neuralgia before surgery,suggesting that the centrality of these brain regions may be the neural basis for this type of pain.Effective surgical procedures may involve changing the centrality of certain brain regions to regulate the neural mechanisms underlying pain perception.In this study,it is found that CTN and ITN have opposite topological changes of neural network,and the reduced efficiency of signal transmission caused by the decreased information concentration in these brain regions,or the decreased adaptability caused by the increased information concentration,will bring adverse(painful)stimuli,and also provide biomarkers for predicting the prognosis of CTN and ITN in the future. |
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