Patient specific selection of lateral wall cochlear implant electrodes based on anatomical indication ranges

Objectives
The aim of this study was to identify anatomical indication ranges for different lateral wall cochlear implant electrodes to support surgeons in the preoperative preparation.
Methods
272 patients who were implanted with a FLEX20, FLEX24, FLEX28, or a custom-made device (CMD) were included in this study. The cochlear duct length (CDL) and basal cochlear diameter (length A) were measured within preoperative imaging data. The parameter A was then employed to additionally compute CDL estimates using literature approaches. Moreover, the inserted electrode length (IEL) and insertion angle (IA) were measured in postoperative CT data. By combining the preoperative measurements with the IA data, the covered cochlea length (CCL) and relative cochlear coverage (CC) were determined for each cochlea.
Results
The measurements of the CDL show comparable results to previous studies. While CDL measurements and estimations cover similar ranges overall, severe deviations occur in individual cases. The electrode specific IEL and CCL are fairly consistent and increase with longer electrodes, but relatively wide ranges of electrode specific CC values were found due to the additional dependence on the respective CDL. Using the correlation of IEL and CCL across electrode arrays, CDL ranges for selected arrays were developed (FLEX24: 31.3–34.4, FLEX28: 36.2–40.1, FLEXSoft: 40.6–44.9).
Conclusions
Our analysis shows that electrode specific CC varies due to the CDL variation. Preoperative measurement of the CDL allows for an individualized implant length selection yielding optimized stimulation and a reduced risk of intraoperative trauma. The CDL, as derived from preoperative CT imaging studies, can help the implant surgeon select the appropriate electrode array to maximize the patient’s outcomes.

研究目标
本研究旨在明确不同侧壁式人工耳蜗电极的解剖适配范围，以辅助外科医生开展术前准备工作。

研究方法
本研究共纳入272例接受FLEX20、FLEX24、FLEX28或定制化装置（custom-made device, CMD）植入的患者。基于术前影像学数据，测量受试者的耳蜗导管长度（cochlear duct length, CDL）与耳蜗基底直径（记为长度A）。随后利用参数A，结合已有文献中的计算方法，估算CDL。此外，基于术后CT数据，测量电极植入长度（inserted electrode length, IEL）与植入角度（insertion angle, IA）。将术前测量数据与IA数据相结合，即可计算得到每侧耳蜗的覆盖耳蜗长度（covered cochlea length, CCL）与相对耳蜗覆盖率（relative cochlear coverage, CC）。

研究结果
本次研究测得的CDL结果与既往研究相符。尽管CDL的实测值与估算值整体区间相近，但个别病例存在显著偏差。不同电极型号对应的IEL与CCL均较为稳定，且随电极长度增加而增大；但由于CC同时受个体CDL的影响，不同电极型号对应的CC区间跨度相对较大。基于不同电极阵列的IEL与CCL之间的相关性，我们推导得到了对应电极阵列的CDL适配区间：FLEX24为31.3~34.4、FLEX28为36.2~40.1、FLEXSoft为40.6~44.9。

结论
本研究分析表明，不同电极型号对应的CC会因个体CDL的差异而有所不同。术前测量CDL可实现个体化的电极长度选择，从而优化刺激效果并降低术中创伤风险。基于术前CT影像获取的CDL数据，可辅助人工耳蜗外科医生选择适配的电极阵列，以最大化患者的术后获益。