| Objective: Hemifacial spasm (HFS) is a common functionaldisorder. The onset is usually in middle or old age. Hemifacialspasm (HFS) is characterized bytonic and clonic contractions ofthe musclesinnervated by the ipsilateral facial nerve. It canpotentially lead to social embarrassment and affect quality oflife. The patients with HFS frequently complain of involuntaryeye closure, which interferes with vision and causes socialembarrassment. Injection of botulinum toxin(BTA) andmicrovascular decompression are two dominating proceduresin many treatments for HFS now. But they have somelimitations. MVP of the facial nerve at the cerebellopontineangle, the most common surgical procedure carried out today,results in markedly improved HFS in the majority of patients.However, a recurrence rate of up to 20% has been reported. Andpotential complications associated with MVP may beunacceptable to some patients. So it is necessary to seek anideally procedure for HFS which is minimum invasion, highlyprecision, safe and effective and low rates of complications.Now stereotactic radiosurgery(SRS) is the preferred procedureof minimum invasive neurosurgery and functional neurosurgery.It is the least invasive treatment option for trigeminalneuralgia(TN), and the complication rate is low, more than 90%of patients maintain normal facial sensation. However until nowwe haven't seen any research of SRS for HFS printed. Ourprevious reseach has proved according to anatomical,pathological, imaging technology that the histologicalexaminations between trigeminal nerve root and facial nerveroot are similar, that the distances between facial nerve root andthe crucial structures around it are far more than 1mm, and thatfacial nerve root can be identified clearly on image usingappropriate technology. The accuracy of gamma knife can reach0.1mm, and it is much fewer than the distances that we havemeasured between the facial nerve root and the crucialstructures around it, so we can concluded that HFS can betreated by SRS and the crucial structures such asvestibulocochlear nerve and brain stem will be free ofirradiation injury. Our animal experiments were performedusing single high-dose photon beam irradiation simulating SRSto rat peripheral nerve of different diameter, to confirm whetherthe radiopathological alterations are similar between large andsmall nerve which have been received same irradiation dose.Our hypothesis was that if the pathological alterations of largeand small nerve of equal length are similar which had beenreceived same dose radiation, we can conclude that the facialnerve(small nerve) should have the same effects to thetrigeminal nerve(large nerve) radiosurgery, and it could toleratethe dose of TN radiosurgery. And we also can conclude that SRScould be used in treatment of HFS.Methods: 36 Sprague-Dawley rats were randomized into 2groups of 18 rats each. The 2 groups are large nerve(sciaticnerve) group and small nerve(posterior tibial nerve) group. Eachrat's nerve was single-dose irradiated with 20, 40, 70Gy ofphonton beam. Each animal's contralateral nerve consisted ofnormal control group. Neurologic and electrophysiologicexaminations were done 1 month and 2 months after treatment.For grading of neurological complications, two different testwere used. Primarily, hind limb motor function was graded.Second, the landing reflex for spread of the toes elicited bylifting the rat by the tail was scored. Electrophysiologic studieswere done under anesthesia using sodium thiopental. Thenhistopathological examinations were performed. Histologicalsections were obtained in both the transverse and longitudinalplanes. Histopathological examinations included: (1)Analyseswith hematoxylin and eosin. (2) Confocal Laser ScanningMicroscopy examination: We used immunoflurescencedouble-labelling technique and confocal laser scanning andpolyclonal antibody S-100 as Schwann cell marker andmonoclonal antibody neurofilament (NF) as axonal marker.(3)Ultrastructural studies were also performed.Results: 1.General observation: Two groups of animals werenot different in general observation. The skin of exposure fieldwas normal in rats received 20Gy dose, and depilation in ratsreceived 40 and 70Gy doses 3 weeks after irradiation, and focalulceration can be observed in 70Gy dose group. But all animalsremained free of neuropathy. Functional evaluation did notdemonstrate a difference between the irradiated limb and thenormal limb. Each sciatic nerve and posterior tibial nerve andmuscles of exposure field were not abnormal in generealobservation. 2. Electrophysiology: The amplitude of actionpotential decreased after irradiation, P<0.05 in 70Gy doseirradiation group, while conduction velocity between controlgroup and irradiation group was not statistical significance. Andthe alterations of both conduction velocity and amplitude ofaction potential were not statistical significance(P>0.05)between large nerve and small nerve in all irradiation group. 3.Histomorphometry: There were not obvious differences betweenlarge nerve and small nerve after irradiation in histopathologystudies using light microscopy, confocal laser scanningmicroscopy and electron microscopy. (1) With hematoxylin-andeosin-stain, nerves that had received 20Gy irradiation doseswere not obvious abnormal, nerves that had received 40Gyirradiation doses exhibited focal myelin pallor, some swellingand vacuolation, microvessels slightly dilatation andproliferation of connective tissue were noted, nerves that hadreceived 70Gy irradiation doses exhibited axonal degenerationand loss, myelin vacuolation, obvious dilatation of endoneuralmicrovessels and epineural vessels were noted. (2) Confocallaser scanning microscopy: using immunofluorescencedouble-labeled identification the immunactivities of antibodyS-100 and antibody of neurofilament decreased in 40Gy and70Gy groups, loss of axon and demyelination can be observed.A significant decrease in axon and myelin were dose related. (3)Ultrastructral studies also exhibited focal demyelination andaxons degeneration related with irradiation doses. Butunmyelinated axons in all groups kept intact.Conclusions: 1. Idiogenetic hemifacial spasm is a commonfunctional disorder. Its aetiology, pathogenesis, histopathologyand clinical procedures resemble to those of trigeminalneuralgia. The experiences of SRS for TN are the theory basis ofSRS for HFS. SRS for HFS by targeting proximal facial nerveroot is feasible. 2. Irradiation-induced injuries are similar inperipheral nerves including cranial nerve. The histologicaleffects are dose related. The peripheral nerves after irradiationdemonstrated axonal degeneration, demyelination and changesof microvaculature. 3. Similar histopathological and electro-physiological changes were observed in the large and smallnerves, so we believe facial nerve root can tolerate theirradiation dose used in SRS for TN, and SRS for HFS can usethe doses of TN treatment for reference. 4. It is hopeful that SRSbecome the ideal procedure for HFS because of its minimum... |
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