Intracranial Segment Imaging Anatomy Of Facial Nerve And MRI Diagnosis On The Hemifacial Spasm

Objective:With high-resolution CT and MR 3D imaging technology,the intracranial segment of facial nerve was displayed and their anatomic data were measured.The relationship with their surrounding blood vessels were analyzed,it is to explore the etiopathogenesis of hemifacial spasm（HFS）and to evaluate the clinical application of MRI.Method:1.to collect the imaging data of 40 subjects who underwent temporal bone high resolution spiral CT scan and brainstem and nerve of MRI with T₁WI-3D-FFE,T₂WI-3D-DRIVE and B-TFE sequence.With the image post-processing,to display and measure the length and diameter of the facial nerve cisternal segment and each segment inside the temporal bone,the angle of facial nerve between transverse axial and oblique sagittal angles were also measured,and statistical analysis was performed.2.The magnetic resonance imaging data of 80 patients with unilateral primary hemifacial spasm were retrospectively analyzed.All the patients underwent T₁WI-3D-FFE,T₂WI-3D-DRIVE and B-TFE scan of the facial nerve.Compared with healthy controls group and hemifacial spasm in patients with symptomatic and non-symptomatic lateral facial nerve and peripheral vascular relationship,facial nerve root to determine whether there is vascular contact or oppression,to identify responsible vessels.3.To compare the positive rates of MRI with T₁WI-3D-FFE,T₂WI-3D-DRIVE and B-TFE in identifying the responsible vessel of primary hemifacial spasm and analyze its clinical value.Results:1.CT scan of temporal bone and MRI of brain stem（T₁WI-3D-FFE,T₂WI-3D-DRIVE and B-TFE sequence）clearly showed the anatomy of facial nerve.The cisternal segment of facial nerve was 13.33±1.46mm,internal auditory canal segment9.98±1.03mm,labyrinth segment 4.97±0.36mm,tympanic segment 10.97±1.53mm,mastoid segment 14.97±1.31mm.The diameters were 1.47±0.35mm for cisternal segment,1.44±0.36mm for internal auditory canal segment,1.16±0.23mm for labyrinth segment,1.28±0.37mm for tympanic segment and 1.39±0.26mm for mastoid segment.There is no significant difference between this study and the statistics of autopsy of domestic and foreign scholars（P﹥0.05）.2.Among the 80 patients with unilateral primary hemifacial spasm,71patients were diagnosed as symptomatic by T₂WI-3D-DRIVE scan,the positive detection rate was88.75%.T₁WI-3D-FFE detection of HFS patients with symptomatic responsibility vessels 77 cases,the positive detection rate was 96.25%.B-TFE detection of HFS patients with symptomatic responsibi-lity vessels 46 cases,the positive detection rate was 57.5%。The distributions of responsible vessels were:49 cases originating from the inferior cerebellar artery,22 cases of the posterior inferior cerebellar artery,10 cases of basilar artery,and 19 cases of vertebral artery.3.There was a statistically significant difference in the diameter of the facial nerve roots between the HFS symptomatic side and the control group（P﹤0.05）,the difference in the length of facial nerve cisternal segment,the angle of horizontal axis and the angle of oblique sagittal plane between the HFS symptomatic side and the control group were not statistically significant（P﹥0.05）.there was significant difference in the root diameter of the facial nerve and the angle horizontal axis between the HFS symptomatic side and the non-symptomatic side（t values were-7.56and-2.03,P﹤0.05）,and no significan difference in the length of facial nerve cisternal segment,the angle of oblique sagittal plane（t=0.79 and0.33,respectively,P﹥0.05）;the degree of symptomatic spasm of HFS and the pressure of the responsible vessels on the facial nerve Degree of correlation（χ²=8.61,P﹤0.05）.Conclusion:1.High resolution spiral CT scan of temporal bone combined with an advanced post-processing workstation for image reconstruction in any orientation and angle can clearly show the morphology and walking of the facial nerve canal,it is good consistency with the autopsy and can conducive the study of facial nerve temporal bone segment.MRI with T₁WI-3D-FFE,T₂WI-3D-DRIVE and B-TFE sequences of brain stem nerve scan can directly show the segment of cisternal and internal auditory canal,the method is reliable.2.With the anatomical observation and measurement of the intracranial segment of facial nerve,the relation between the facial nerve and the surrounding vessels are showed.Abnormal positions of vessels are one of the main causes of primary hemifacial spasm,they provide the anatomical basis for clinical diagnosis,treatment and postoperative curative effect.3.There is a close relationship between the responsibility vessel contact or compression of the root of facial nerve and the occurring of clinically facial spasm symptoms.The B-TFE sequence in showing the facial nerve is better than the other sequences,but it shows a poor ability to display small vessels.T₁WI-3D-FFE imaging can display both of facial nerve and peripheral vessels.It can be used as a standard for diagnosing on the primary hemifacial spasm.The T₂WI-3D-DRIVE can clearly show the facial nerve with cerebrospinal fluid,but it shows a little poor ability of small blood vessels,which can be used as a supplement to T₁WI-3D-FFE;the combination of the two scan sequences helps to increase the credibility of the displayed results.