Retrospective Evaluation of a Technique for Patient-Customized Placement of Precurved Cochlear Implant Electrode Arrays

Abstract

Objective Precurved electrode arrays (EAs) are commonly used in cochlear implants (CIs). Modiolar placement of such arrays has been shown to lead to better hearing outcomes. In this project, we retrospectively evaluated the modiolar positioning of EAs within a large CI imaging database. We aimed to discover the rate at which perimodiolar placement is successfully achieved and to evaluate a new technique we propose to preoperatively plan patient-customized EA insertion depths to improve perimodiolar placement at the time of surgery. Study Design Retrospective chart review and radiographic analysis. Setting Single tertiary academic referral center. Subjects and Methods Ninety-seven CI ears were evaluated. Perimodiolar positioning of electrodes was quantified using pre- and postimplantation computed tomography scans and automated image analysis techniques. Results Average perimodiolar distance was 0.59 ± 0.18 mm. Disagreement between the actual and our recommended insertion depth was found to be positively correlated with perimodiolar distance ( r = 0.49, P < .0001). Conclusions These results show that the average CI recipient with a precurved EA has a number of electrodes distant to the modiolus where they are not most effective. Our results also indicate the approach we propose for selecting patient-customized EA insertion depth would lead to better perimodiolar placement of precurved EAs.

Keywords: 3D image analysis; cochlear implants; image-guided surgery.

Figure 1

(a) An electrode insertion that is too deep (blue dotted curve). (b) An electrode insertion that is too shallow (blue dotted curve).

Figure 2

Shown are the modiolar curves (green), and the actual electrode positions for each of 3 subjects (blue dotted curves) with increasing average distance between electrodes and modiolus.

Figure 3

The geodesic distance between those two projected points along the modiolar curve is shown as $G(E_d,{\widehat{E}}_d)$.

Figure 4

(a) Histogram of our modiolar distance results $\left\{\overline{M}\right\}$. (b) Histogram of the geodesic distance between recommended and actual insertion depths $\{G(E_d,{\widehat{E}}_d)\}$.

Figure 5

Scatter plot of the relationship between $\overline{M}$ and $|G(E_d,{\widehat{E}}_d)|$ with linear regression line shown in black.