Using OTOPLAN to estimate the angular insertion depth for patients with a FLEXsoft electrode array from MED-EL

Introduction OTOPLAN uses radiological images to estimate the length of the cochlear duct (estCDL) and the insertion depth preoperatively. Based on these calculations surgeons can choose the appropriate length of the electrode array before implantation. In our clinic nearly every patient, who received a cochlear implant (CI) from MED-EL, got the FLEXsoft (which was the longest electrode array at the time of our study), as long as their radiological images didn't show any cochlear malformation. This study aims to examine, whether OTOPLAN can predict the maximum angular insertion depth (maxAID) of the electrode array correctly for patients with FLEXsoft.

Material and methods Seventy-two ears, who underwent a CI implantation with MED-EL FLEXsoft, were included in this study. Preoperative CT images were used to estimate the estCDL and maxAID with OTOPLAN. Afterwards the actual maxAID was defined on the basis of the postoperative X-ray image (Stenvers).

Results Although a statistical correlation between the with OTOPLAN preoperatively predicted maxAID and the actual postoperative maxAID was found (R=0.43, p=0.004), there is still a difference of 46.9±9.1°. For ears with a rather small cochlear (estCDL<35 mm) and thereby predicted maxAID>720° OTOPLAN seems to overestimate the maxAID systematically.

Discussion A potential explanation for the overestimation of the maxAID by OTOPLAN could ascribe to the fact that the diameter of the round window (RW) in a rather small cochlear is less than the diameter around the end ring of the electrode array, which could lead to a systemic offset between the end ring and RW. Taking this in consideration for ears with a predicted estCDL<35 mm an offset of 2.5 mm would compensate the overestimation.

Publication History

Article published online:
19 April 2024