The Estimated Value Of Temporal Bone CT For Complexity And Neurological Injury In Cochlear Implantation

ObjectiveCochlear implantation is an effective way to restore hearing for patients with both sides severe to profound sensorineural hearing loss. But due to individual differences and anatomical variations of the facial nerve, the difficulty of posterior tympanotomy often be encountered with the risk of un-exposure of round window and damage of both chorda tympani nerve and facial nerve. To study the relationship between the most opening wide range of facial nerve recess displayed by temporal bone high resolution CT and the chorda and facial nerve actual distance measured in the surgery, and explore the assessment value of CT in cochlear implantation before surgery, we conducted this study.Methods80cases from national project of cochlear implants had been completed their operation in the first affiliated hospital of Zhengzhou university from September2012to December2012. Among them, there were43male and37female,41on the left ear and39on the right, aged from13months to6years old with the average3.2 ±0.13years old. No middle ear and inner malformation had been found by temporal bone high resolution CT before surgery. To compare the difference, the vertical distance from facial nerve vertical section front to external auditory meatus back wall at the round window niche level of the axial position CT scan of temporal bone were recoded and the distance from outlined facial nerve tube to the outlined chorda tympani nerve tube at the round window niche level were measured during the surgery, repeating three times for averaged measurements. Using SPSS17.0statistical software for statistical analysis. Data were expressed in mean±standard deviation and were going for person linear correlation and regression analysis. Ear and gender were lined for independent sample t test.ResultsIn the round window niche level of axial temporal bone CT in80cases of cochlear implantation children, the average distance (take it as AB) from facial nerve to external auditory meatus back wall was (4.04±0.22) mm. The average measured distance (take it as CD), from vertical section of outlined facial nerve tube to outlined chorda tympani nerve tube corresponding to round window niche level during the operation, was (2.35±0.28) mm. The average distance difference between the two measurement above was (1.70±0.18)mm. The difference between gender, as well as ear side had no statistical significance (p>0.05). The correlation and regression analysis of the two measurement data showed a positive correlation and the correlation coefficient was r=0.791, the simple linear regression equation was AB=0.616*CD+2.595. Accordingly, when the intraoperative measured distance was1.5mm, which means below that the operation will be very difficult according to the measurement and the most surgeon’s experience, the distance from facial nerve to external auditory meatus back wall measured by CT image was3.5mm. ConclusionThe average difference about the distance from facial nerve to chorda tympani nerve at the round window niche level estimated by CT and measured in the surgery was (1.70±0.18)mm in1to6years old children with cochlear implants, which suggests that we should think about the difference before surgery.The two groups data of the distance from facial nerve to chorda tympani nerve at the round window niche level estimated by CT and measured in the surgery are positive correlation. When the distance is less than3.5mm estimated by CT, the actual distance in the surgery will be less than1.5mm, which suggests the difficulty in the operation and the increased risk of nerve injury.