Digital live imaging of intraoperative electrocochleography during cochlear implantation: the first 50 patients

Abstract

Introduction: Real-time visualization of intraoperative electrocochleography (ECochG) potentials via a digital microscope during cochlear implantation can provide direct feedback during electrode insertion. The aim of this prospective, randomized study of 50 patients was to obtain long-term data with a focus on residual hearing preservation and speech understanding.

Material and methods: Cochlear implantations were performed in 50 patients (26 female, 24 male) with residual hearing using a digital microscope. Patients were randomized into two groups. Intraoperative ECochG potentials were either displayed directly in the surgeon's field of view (picture-in-picture display, PiP) or not directly in the field of view (without picture-in-picture display, without PiP). Residual hearing preservation and speech comprehension were recorded within a 1-year follow-up period, compared between groups (PiP versus without PiP) and to a control group of 26 patients implanted without ECochG.

Results: Mean insertion time was significantly longer in the picture-in-picture group (p = 0.025). Residual hearing preservation after 6 weeks at 250 Hz was significantly better in the picture-in-picture group (p = 0.017). After one year, 76% of patients showed residual hearing in the picture-in-picture group (62% without picture-in-picture technique, p = n.s.). Use of the picture-in-picture technique resulted in better long-term pure tone residual hearing preservation at 250, 500, and 1000 Hz. Speech intelligibility improved by 46% in the picture-in-picture group (38% without picture-in-picture).

Discussion: This study is the first to describe long-term results in a large cohort of cochlear implant patients in whom digital visualization of intraoperative ECochG was used. Our results show that visualization of intraoperative ECochG has a positive effect on residual hearing preservation.

Keywords: Cochlear implantation; Digital microscopic imaging; Hearing preservation; Intraoperative electrocochleography.

Fig. 1

Intraoperative setting. Center of the intraoperative setting is the digital microscope. During electrode insertion, residual hearing is monitored by ECochG potentials measured as Cochlear microphonics which are transferred via a video converter from a laptop to the digital microscope and visualized in the top right corner in the surgeon’s field of view. Patients´ CT scans are displayed in the top left corner. Postoperative control for correct intracochlear positioning of the electrode is performed with C-arm X-ray-unit (left side)

Fig. 2

Residual hearing preservation over a 1-year follow-up-period. In the picture-in-picture group, the percentage of patients with residual hearing ranged from 96% 6 weeks postoperatively to 76% at the end of the follow-up period. In the without picture-in-picture group, 62% of patients showed residual hearing at the end of the follow-up period. Differences between groups were significant 6 weeks postoperatively (Chi-Square test, p = 0.017, chi = 8.08). At 3 months (p = 0.64, chi = 0.21), 6 months (p = 0.69, chi = 0.15) and 12 months (p = 0.46, chi = 0.52) postoperatively, no significant differences between groups were detected

Fig. 3

Results of AGF over a 1-year follow-up period. In the tested frequencies (250, 500 and 1000 Hz), AGF-results of the PiP-group showed a slightly better hearing threshold than the without PiP-group without reaching statistical significance (intraoperative: 250 Hz: p = 0.46, z = 0.74; 500 Hz: p = 0.83, z =  − 0,21; 1000 Hz: p = 0.27, z = 1.09, 6 weeks: 250 Hz: p = 0.55, z = 0.59; 500 Hz: p = 0.35, z = 0.93; 1000 Hz: p = 0.43, z = 0.78, 3 months: 250 Hz: p = 0.83, z = 0.21; 500 Hz: p = 0.18, z = 0.32; 1000 Hz: p = 0.31, z = 1.01, 6 months: 250 Hz: p = 0.29, z = 1.05; 500 Hz: p = 0.45, z = 0.75; 1000 Hz: p = 0.16, z = 1.39, 12 months: 250 Hz: p = 0.35, z = 0.93; 500 Hz: p = 0.39, z = 0.84; 1000 Hz: p = 0.24, z = 1.16)

Fig. 4

Pure tone thresholds and AGF over a 1-year follow-up period in patients with intraoperative ECochG- and without (regular implantation). At 250 Hz, AGF results differ significantly from pure tone thresholds over the follow-up period (6 weeks: p < 0.01, z = 3.61; 3 months: p < 0.01, z = 3.72; 6 months: p < 0.01, z = 5.4; 12 months: p = 0.04, z = 2.04). At 500 Hz (6 weeks: p = 1, z = 0; 3 months: p < 0.1, z = 1.61; 6 months: p = 0.01, z = 2.5; 12 months: p = 0.32, z = 0.97) and 1000 Hz (6 weeks: p = 0.5, z = 0.6; 3 months: p < 0.24, z =  − 1.1; 6 months: p = 0.05, z = 1.9; 12 months: p = 0.76, z = 0.29), a significant difference was detected only after 6 months. Residual hearing preservation is non-significantly better in patients implanted with intraoperative ECochG compared to the control group of patients implanted regularly without ECochG, especially at 1000 Hz (pre/intraoperative: 250 Hz: p = 0.53, z =  − 0.62; 500 Hz: p < 0.77, z =  − 0.29; 1000 Hz: p = 0.4, z = 0.83; 3 months: 250 Hz: p = 0.23, z =  − 1.19; 500 Hz: p = 0.69, z = 0.39; 1000 Hz: p = 0.59, z = 0.53)

Fig. 5

Speech understanding tested with Freiburger monosyllables before (best-aided condition) and after implantation. A significant improvement in speech understanding after one year compared to preoperative results was detected in both groups (PiP: p < 0.01, z =  − 3.72; wPiP: p = 0.017, z =  − 2.39) without a significant difference between groups