| Background:Cochlear implantation(CI) is the most effective treatment of severe and profound sensorineural hearing loss, more and more deaf patients benefit from it. High-resolution temporal bone CT (HRCT) can clearly show the bone structure of the temporal bone and cochlear morphology, it is an important assessment tool before cochlear implantation, it is significant for evaluation of surgery preoperatively, decising of surgical plan and improving postoperative rehabilitation.With the of development of cochlear implant,temporal bone CT examination has been developed rapidly, from a simple and intuitive two-dimensional image to Multiplanar reconstruction(MPR), cueved reconstruction, volume rendering technique (VRT), three-dimensional reconstruction (3-D reconstruction), CT virtual endoscopy reconstruction (CTVE), maximum intensity projection reconstruction (MIP), minimum intensity projection reconstruction (MinP) and so on, and from observing the inner ear morphology to more accurate measuring morphology in perioperative period, it help surgeons to understand the morphology and anatomy of the cochlea, assess the difficulty of the surgery and provide an objective basis for understanding the situation of electrod after implantation. The principle of cochlear implantation is to convert acoustic signals into electrical signals, using implant electrodes inside the cochlea to provide stimulation to remaining auditory nerve. The frequency of human cochlea exponentially distributed along the basement membrane:high-frequency area is located in the bottom turn and the low-frequency is targeted at the top turn. Cochlear frequency characteristic associate with the cochlea length, although there are differences between the length of the cochlea in different individuals, the same percentage of lengthown the maximum sensitive frequency. It has been reported that if the frequency of implantation electrode matched the corresponding acoustic nerve,the speech discrimination score will be improved; It can broaden the field of pure tone average and improve sensibility of tonal language when the implanted electrodes laid in the cochlea is increased;When the distance of electrode between the bottom and the top in cochlea is broaden, the interference betwwen the signal of adjacent electrode will be reduced in result of impovement of speech discrimination score in noise by using language processors; Through implanting electrodes deeply, it can stimulate and sustain more spiral nerve cells’activity, and a wider range of auditory will be activating, which provide development conditions for the children’s auditory center. On the other hand, Therefore, how to get the exactly length of the cochlea is critical. However, the cochlea is deeply located in the temporal bone with the character of complex structure,tilted position and large variation, the measurement of cochlear morphology is difficulty in directly. So far, many researchers are dedicated to investigate the structure of labyrinth in histology and iconography for seeking a non-invasive method to mearsue the cochlear morphology, and have obtained some results at present. Because of the lack of uniform measurement standard, different Research Unit adopt different tomography equipment and methods, and the majority of the measurement method are complicated and time-consuming in result of limiting the measurement to popularize in the clinical;In domestic,the cochlear electrode length is designed based on the data of Westerners, and the length of the cochlea there are differences between different ethnic, foreign scholars’measurement data is not suitable for the Chinese people. Therefore,it is necessary to focus on choosing appropriate method to measure the length of the cochlear duct in large-scale and design appropriate electrode.The classical surgery of cochlear implantation is implanting the electrode through the facial nerve recess,it contains opening the facial recess and exposing the round window niche or round window membrane, implanting the electrode into the cochlear scala tympani. The preoperative HRCT temporal bone helps surgeon to understand the facial nerve recess, by locating the vertical segment of the facial nerve, external auditory canal latter wall, round window and other cochlear structures, as a reference to guide clinical surgery. Research showed that there is no significant difference between the adults and children in width of facial recess, children can be performed the cochothlear implantation as well. In the case of fully exposing facial nerve recess and the round window niche or round window membrane, how to choose the suitable location to implant electrode is crucial, and the orientation of the cochlea may affect the degree of exposuring surrounding structures. Traditionally,although the width of facial recess don’t change with age,and there is no significant difference between the adults and children in width of facial recess, in fact,the orientation of cochlea and semicircular canals can be changed with age, some researcher believed that the angle of cochlea basal turn was gradually decreasing with growth, which the most variation was in the11-15group, and women might had been completed the of development of skull in earlier age. The study showed that comparing with adults, the angle of external auditory canal and cochlear basal turn is narrow in children, and the age of direction of cochlear basal turn and ideal cochlear implant path is wide, with a more obtusely angled basal turn, the electrode will tend to abut against the anterior wall of the basal turn as it passes through the cochleostomy, making insertion potentially more difficult, resulting in much more significant cochlear damage.However, in domestic, the most research remains focusing on the anatomy of facial nerve recess and scala tympani regions, there is few literature about the morphology of cochlear, which is necessary for understanding relative anatomy and assessment of surgery systematically.Objective:To explore the value of High-resolution temporal bone CT (HRCT) multi-planar reconstruction technique for measuring the relative parameter of cochlear morpholog in the standard cochlear view and preoperative assessment of cochlear implantation.Method:We retrospectively collected80cochlear implant patients’data in our hospital.The groups were investigated in our reserch according to the patient’s sex, age and whether the inner ear is malformation or not. Temporal bone HRCT multi-planar reconstruction (MPR) was applied to analyze the measurement parameter in the standard orientation of the cochlea image:the largest distance from the round window to the lateral wall (distance A), the perpendicular distance (B) and angle of the basal turn of the cochlea relative to the midsagittal plane(y).Evaluating the reproducibility of the measured data and comparing the results between the different groups. In normal inner ear, the cochlea under standardized orientation map for each measured parameter values in gender, age group comparison and correlation analysis between; between the parameter values under standardized orientation chart compares the cochlea of the inner ear and the inner ear malformation normal group; using the measured cochlear parameter values and formulas applied mathematical model to calculate the length of the cochlear duct, and the measurement results of related studies abroad were analyzed and compared.Results:1.The measurements of A, B and γ LOA value was0.32mm,0.27mm and4.3°in different observe; the A, B and y LOA value was0.25mm,0.25mm,3.3°bewteen intraobserver, Bland-Altman analysis showed that the majority of the measured values were in the95%confidence interval.2.1n the normal cochlea group, the overall cochlear A, B, and y value was8.69×0.41mm,6.44±0.38mm and59.97±4.16°; males’A, B and γ values was8.79±0.34mm,6.58±0.28mm and59.82±3.92°; females’A, B, and γ values was8.53±0.47mm,6.22±0.43mm,60.22±4.60°. Males’cochlear distance A (8.79±0.34mm) and perpendicular distance B (6.58±0.28mm) were significantly larger than A (8.53±0.47mm) and B (6.22±0.43mm) in females’(P<0.05), but the angle y was no significant difference between two groups(P>0.05).3. The Cochlear distance A and perpendicular distance B was compared between the different age groups, there was no significant difference between the different age groups about A and B(P=0.509, P=0.419). Analysis of the values and different age groups, a positive correlation between the A and B values (r=0.43, P<0.01),y was negatively correlated with age.The results showed the basal turn angle y was gradually decreasing with the age increases(r=-0.25, P<0.05), and in the2-4and5-10years’group,the angle changed obviously, and the basal turn angley’standard deviation was larger in the2-4years’group.4. The result showed that the cochlear distance A and the angle y both were no statistically different between the normal and malformation group(P=0.58, P=0.56), there was significant difference between between two groups when compared with B (P=0.01), the perpendicular distance B was smaller in malformation group than normal group5. The Cohlear distance A value was smaller than the results of foreigner in Standard Cochlear View; Through the calculation formula:2TL=3.65×A-3.63, it showed that the measured value was similar with Chinese research results.Conclusion1、The use of High-resolution temporal bone CT, multi-planar reconstruction technique (MPR) and minimum intensity projection (Minp) technology for geting the Standard Cochlear View was viable, it could accurately measure the morphological parameters of cochlea, the method was simple and had good reproducibility and deserved the clinical application.2、To analysis of the measurement results of the length of cochlea, males’ cochlear length was more longer than females’,and Chinese people’length of the cochlea was shorter than Westerners, this was valuable for designing personal electrode for Chinese.3、By compariing with studies in china,the multi-planar reconstruction technique (MPR) technology and the computational formulation were comparable exact.4、The results showed the basal turn angle y was gradually decreasing with the age increases, and in the2-4and5-10years’group,the angle changed obviously, and the basal turn angley’standard deviation was larger in the2-4years’group, this trend can provide some help to guide clinical work. |
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