Abstract
ObjectivesThe aim of this study was to identify anatomical indication ranges for different lateral wall cochlear implant electrodes to support surgeons in the preoperative preparation.Methods272 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.ResultsThe 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).ConclusionsOur 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.
Highlights
Cochlear implantation is a technology for patients with total, severe or frequency specific hearing loss which can restore the patient’s ability to understand speech [1,2]
While cochlear duct length (CDL) measurements and estimations cover similar ranges overall, severe deviations occur in individual cases
Using the correlation of inserted electrode length (IEL) and cochlea length (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)
Summary
Cochlear implantation is a technology for patients with total, severe or frequency specific hearing loss which can restore the patient’s ability to understand speech [1,2]. The cochlear implant (CI) works by directly stimulating the auditory nerve This is accomplished by inserting a cochlear implant electrode array into the patient’s cochlea. Various types of electrode arrays from different manufacturers are available These electrode arrays differ in size, length, number of electrode contacts and material characteristics [3]. Previous studies have shown that for patients who only hear with their CI, improved outcomes after CI surgery can be expected with longer electrode arrays and deeper insertion angles [23,24,25]. Other studies have shown that the insertion angle depends on the electrode array type and on the length of the cochlea [26,27]. Dysplasia and other syndromes exist which have an effect on cochlear geometry, especially regarding the length, shape and number of turns (e.g. Mondini dysplasia) [28]
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