Clinical values and advances in computed tomography evaluation after cochlear implantation
GU Wenxi,1,2,3, JIA Huan1,2,3, WU Hao,1,2,3
1.Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
2.Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai 200125, China
3.Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200125, China
Cochlear implantation has been a standard rehabilitation for children and adult patients with severe to profound sensorineural deafness. The intracochlear localization of the electrode array is one of the key factors related to the postoperative auditory and speech outcomes. Preservation of the residual hearing is related to the trauma to the inner ear structures caused in the insertion process. Optimal insertion depth and positioning of the electrode array is important for frequency discrimination. The post-operative position of the electrode array is evaluated by using plain X ray or computed tomography (CT). Compared to the plain X ray, CT produces three-dimensional (3D) imaging. With the application of post-operative CT evaluation, the integrity of the electrode array can be verified for surgical safety and improving programming accuracy. Different 3D reconstruction techniques and methods based on the post-operative CT imaging have been proposed to facilitate the precise recognition of position of each electrode, thus helpful to evaluate the possible insertion trauma to inner ear structures and the potential effect on auditory and speech outcomes. The post-operative CT evaluation has helped the electrode array design, brought progress to the soft surgery procedure and promoted new technologies such as robotic surgery and navigation. Therefore, it is getting more and more attention. This article reviews the clinical application values and the progress of techniques in post-operative CT evaluation of cochlear implantation.
对于内耳解剖结构正常的植入者，将电极正确植入耳蜗内并不十分困难。但患者存在内耳解剖结构畸形的情况时，可能会影响电极的正常植入，需要完善术后CT影像学检查，判断电极与耳蜗的位置。据报道［9］，植入人工耳蜗电极的儿童患者中有近1/3存在不同程度的内耳畸形。例如CHARGE综合征的患儿由于常存在中耳解剖异常，导致人工耳蜗植入术中解剖标志辨认欠清；BIRMAN等［10］对该类患儿进行人工耳蜗植入术后的CT影像显示，电极未能植入耳蜗底圈，停留在圆窗龛附近，还在鼓室腔里未进入内耳。耳蜗分隔不全Ⅲ型（incomplet partition type Ⅲ，IP-Ⅲ）的患者耳蜗和内听道没有骨性分隔，导致电极可能从耳蜗滑入内听道［11］。此外，即使内耳形态正常，当耳蜗开窗角度不正确时，电极也可能误入前庭或半规管［12］；亦有由于术中下鼓室气房影响圆窗辨认，进而导致电极植入颈动脉管或咽鼓管［13］的报道。诸如此类的错误植入位置导致人工耳蜗无法发挥作用，甚至可能危害患者的健康。因此有必要完善术后CT影像学分析判断电极是否植入耳蜗，为必要时取出电极、重新植入提供临床依据，并预防严重并发症的出现。
Note： A. Sagittal view; the blue line passing the cochlear turn at 90° and 270°. B. Axial view; the blue line passing the center of round window (0˚) and cochlear turn at 180˚; an extra-cochlear electrode (red arrow). C. Coronal view showing the full length of the electrode array; insertion depth angle of the electrode array was 348˚ with the center of the axes at the center of the cochlea modiolus. Black arrow—the most apical electrode; RW—round window.
Fig 1
Insertion depth angle determined by the 3D MPR mode in medical image viewers
Note： A. Electrodes in the scala tympani. B. Electrodes in the scala vestibuli. C. Unable to determine the electrode array positioning. The red dotted lines mark the basal turns of cochlea and the blue dotted lines mark the middle of the basilar turns, i.e., the basal membranes. When the electrodes were above the blue line, they were supposed to be in the scala vestibuli; when they were below the blue line, they were supposed to be in the scala tympani.
Fig 2
Analysis of the electrode arrays positioning relative to the basilar membrane in medical image viewers
Note：3D model of the electrode array and basilar membrane constructed by using a reconstruction fusion software is shown in the right below part. The electrode array (in blue) was fully under the basilar membrane (in red), suggesting a complete scala tympani insertion.
Fig 3
Analysis of the electrode array positioning relative to the basilar membrane by the self-created 3D reconstruction fusion software
GU Wenxi participated in the conception and drafted the original manuscript; JIA Huan participated in the review and editing; WU Hao conceived the idea and participated in the review and editing. All the authors have read the last version of paper and consented for submission.
利益冲突声明
所有作者声明不存在利益冲突。
COMPETING INTERESTS
All authors disclose no relevant conflict of interests.
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