| ObjectiveHemifacial spasm (HFS) is a common functional disorder. The onset is usually in middle or old age. HFS is characterizek bytonic and clonic contractions of the musclesinnervated by the ipsilateral facial nerve. It can potentially lead to social embarrassment and affect quality of life. The patients with HFS frequently complain of involuntary eye closure, which interferes with vision and causes social embarrassment. Injections of botulinum toxin (BTA) and microvascular decompression are two dominating procedures in many treatments for HFS now. But they have some limitations. MVP of the facial nerve at the cerebellopontine angle, 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. And potential complications associated with MVP may be unacceptable to some patients. So it is necessary to seek an ideally procedure for HFS which is minimum invasion, highly precision, safe and effective and low rates of complications of minimum invasive neurosurgery and functional neurosurgery. It is the least invasive treatment option for trigeminal neuralgia (TN), and the complication rate is low, more than 90% of patients maintain normal facial sensation. However until now we haven't seen any research of SRS for HFS printed. Out precious research(partâ… ) had proved according to anatomical, pathological, imaging technology that the histological examinations between trigeminal nerve root and facial nerve root are similar, that the distances between facial nerve root and the crucial structures around it are far more than 1mm, and that facial nerve root can be identified clearly on image using appropriate technology. The accuracy of gamma knife can reach 0.1mm, and it is much fewer than the distances that we have measured between the facial nerve root and crucial structures around it, so we can concluded that HFS can be treated by SRS and the crucial structures such as vestibulocochlear nerve and brain stem will be free of irradiation injury. Out precious research(partâ…¡) had proved according to pathological, electrophysiology that similar histopathological and electrophysiological changes were observed in the large and small nerves, so we believe facial nerve root can tolerate the irradiation dose used in SRS for TN, and SRS for HFS can use the doses of treatment for reference. Our animal experiment was to investigate the pathogenesis in hemifacial spasm by establishing animal models of hemifacial spasm and combining with electrophysiologicaland pathologic technique. And the experiment proved important rationale that SRS is used in treatment of HFS.Methods1 Grouping and establishing animal models: 30 NEW Zealand white rabbits were randomized into four groups: 15 rabbits underwent both artificial demylination and artificial compression (model group). 5 rabbits underwent only arterial compression, 5 rabbits underwent only artificial demyelination and 5 rabbits underwent sham-operation control. Along the underside and back of left ear, the skin is cut. And facial nerves were uncovered with using operating microscope. Pulverized 3-0 catguts of chrome was placed around of facial nerve stem. Then superficial temporal arteries were separated. For arteries impinge on nerve, gelatin sponges were under the arteries, and tunica adventitia vasorum was dangled with 6-0 sutures. It was success that facial nerves stem pulsate with throb of arteries. Facial nerves of the group that only arterial compression were compressed with superficial temporalarteries. To the group that underwent only artificial demyelination, Pulverized 3-0 catguts of chrome was placed around of facial nerve stem just. Superficial temporal arteries of sham-operation control group were separated only. Abnormal muscle response (AMR) changes in all groups were tested and compared at the third or sixth week after operation respectively. 2 Electrophysiology: Abnormal muscle response (AMR) is characteristic for hemifacial spasm that electromyogram can be noted from other ramus of facial nerve when one ramus is excited. It is mean that there is relation between facial nerve fiber and facial motor neuron.3 Analyses with hematoxylin and eosin.4 Ultrastructural studies were also performed.Results1 General observation: The facial nerves of the rabbits underwent only arterial compression and the rabbits underwent sham-operation control were similar with normal rabbits'. The model group and the rabbits underwent only artificial demyelination'facials were redder and more loosen than normal facial nerves.2 Electrophysiology: No AMR was recorded in all four groups at the third week after operation, while a clear AMR was evoked in model group rather than in the other groups at the sixth week after operation.3 Histomorphometry: The facial nerves of the rabbits underwent only arterial compression and the rabbits underwent sham-operation control were no different with normal rabbits'in histopathology studies using light microscopy and electron microscopy. (1) With hematoxylin-and eosin-stain, the model group and the rabbits underwent only artificial demyelination'facial nerves were obvious change, discontinuity and axon swell or disappear and myelin loose or disappear. (2) Ultrastructural studies: the model group and the rabbits underwent only artificial demyelination'facial nerves exhibited plies of myelin separate, curl and myelin disappear partly or entirely. Axon pychosis and degeneration.Conclusions1 A clear AMR was evoked in model group rather than in the other groups at the sixth week after operation, and facial nerves demyelination could be observed using electron microscopy, while no same result was observed in other groups. So we believe the facial nerve demyelination and vascular compression are both needed to induce hemifacial spasm essentially.2 Facial nerve is damnified chronically by artificial compression. The nervous tissue ischemia and anoxia are produced by disturbance of circulation, and blood-nervous tissue barrier is destroyed. Later, endoneurium edema occurs and facial nerve demyelination occurs.3 The study provides credible rationale for the study that HFS is treated by SRS with the HFS animal model. Idiogenetic hemifacial spasm is a common functional disorder. Its aetiology, pathogenesis, histopathology and clinical procedures resemble to those of trigeminal neuralgia. The experiences of SRS for TN are the theory basis of SRS for HFS. SRS for HFS by targeting proximal facial nerve root is feasible.4 It is helpful that SRS become the ideal procedure for HFS because of its minimum invasion, highly precision, safe and effective and lower rates of complications. |
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