Investigation Of Petrous Ridge And Trigeminal Nerve In Trigeminal Neuralgia Without Neurovascular Compression

BackgroundTrigeminal neuralgia(TN)is one of the most common painful diseases in the facial region.Its main clinical manifestations are periodic and recurrent bursts of transient shock pain,which can affect the area innervated by one or several trigeminal nerve branches and seriously affected the daily life and work of patients.Nowadays TN was regarded as a pathological pain caused by demyelination,and a large number of studies focused on the part of the mechanical stimulation/compression and secondary changes of the nerve.In recent years,studies mainly focused on the subarachnoid blood vessels and its influences on the structure of trigeminal nerve.Neurovascular compression or conflict(NVC)was currently the most widely accepted theory,and based on this theory microvascular decompression(MVD)was one of the important surgical operation methods.The prominent advantage was that this kind of surgery can relieve local compression of vessels and keep the integrality of the trigeminal nerve sensory tracts.Some studies showed that the cure rate of MVD could be up to 80%.Besides MVD could represent an immediate relief postoperatively,which made it widely used.However,during the operation there was no responsible vessel for compression in some patients with trigeminal neuralgia.In addition,some patients with postoperative recurrence were with no recurrence of NVC in MRI.Even in some epidemiological investigations,a certain proportion of NVC was found in the normal population.All these suggested that there may be other mechanisms of TN.Few previous studies explored the relationship between the passage of trigeminal nerve with peripheral structures,but with the emergence of new dissection techniques and the development of magnetic resonance neuroimaging technology,it was feasible to study on the trigeminal nerve trunk,ganglions,and the relationship between three main branches with the surrounding soft tissues and bony structures.PurposeThe aim of this study was to study the skeletal structure of petrous bone and the morphological characteristics of trigeminal nerve in patients with non-vascular compression trigeminal neuralgia by using the three-dimensional magnetic resonance imaging.And we meant to study the influences of the structure around porus trigeminus(trigeminal foramen)on trigeminal nerve,and further explored the anatomical factors of the pathogenesis of trigeminal neuralgia.Besides,we meant to use variables of petrous bone and trigeminal nerve to assist the diagnosis of TN.MethodsA prospective study was conducted for 57 patients with TN in Shandong provincial hospital who were documented with complete personal data and negative MRI result from May 2017 through December 2019.52 cases of controls were included as well.3.0 T Siemens and Philips magnetic resonance imaging scanner were used and MRI image data should include three-dimensional high resolution imaging sequences centering on the route of trigeminal nerve,standard T1-weighted and T2-weighted images.We reconstructed the image from the horizontal and sagittal direction and measured the angle of the petrous ridge(APR),the angle of trigeminal nerve(ATN),and the relative depth(RD)of the root of trigeminal nerve in root entry zone(REZ).Receiver operating characteristic(ROC)analysis was performed to examine the diagnostic performances of APR,ATN and RD for differentiating among patients with TN and healthy control subjects.ResultsIn the 57 cases of patients and 52 cases of controls,APR of the affected side in patients was 98.04°±20.10°,the unaffected side was 105.13°±22.94°,and the average APR of two sides in controls was 108.89°±16.33°.APR of the affected side in patients was smaller than that of unaffected side and controls(P<0.038;P<0.003).ATN of the affected side in patients was 143.78°±10.05° and that of the unaffected side was 149.47°±9.31°.The average ATN of two sides in controls was 151.07°±8.30°.The ATN of the affected side in patients was sharper than that of the unaffected side and controls(P<0.001;P<0.001).RD of trigeminal nerve root of the affected side in patients was-2.05 mm±1.58 mm,the unaffected side was-1.58 mm±1.60 mm,and the average RD of two sides in controls was-1.20 mm±1.49 mm.RD of trigeminal nerve root on the affected side in patients was deeper than that of the unaffected side and controls(P=0.001;P<0.05).Areas under ROC curve(AUC)and 95%Cis for APR,ATN,RD were 0.665(0.563-0.767),0.719(0.623-0.815),0.664(0.562-0.766),and ATN was the most valuable marker with regard to the diagnostic performance for TN without NVC.ConclusionsIn TN patients without NVC,the angle of the petrous ridge(APR)was smaller,the angle of trigeminal nerve(ATN)was sharper,and the relative depth(RD)of trigeminal nerve root was lower in REZ.On the one hand,the sharp petrous ridge may produce local mechanical stimulation which may contribute to the pathogenesis of TN;on the other hand,the angulation of trigeminal nerve could reflect the influence of adjacent structures on morphology of the nerve.The anatomical features of the petrous ridge and trigeminal nerve can be used as a reference for comprehensive diagnosis and evaluation.Especially ATN showed a satisfactory diagnostic performance as a reference.