Background: Cochlear implant (CI) electrode insertion can change the mechanical state of the ear whereby wideband tympanometry absorbance (WBTA) may serve as a sensitive tool to monitor these mechanical changes of the peripheral auditory pathway after CI surgery. In WBTA, the amount of acoustic energy reflected by the tympanic membrane is assessed over a wide frequency range from 226 Hz to 8000 Hz. The objective of this study was to monitor changes in WBTA in CI recipients before and after surgery. Methods: Following otoscopy, WBTA measurements were conducted twice in both ears of 38 standard CI recipients before and in the range of 4 to 15 weeks after CI implantation. Changes from pre- to postoperative absorbance patterns were compared for the implanted as well as the contralateral control ear for six different frequencies (500 Hz, 750 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz). Furthermore, the influence of the time point of the measurement, surgical access, electrode type, sex and side of the implantation were assessed for the implanted and the control ear in a linear mixed model. Results: A significant decrease in WBTA could be observed in the implanted ear when compared with the contralateral control ear for 750 Hz (p < 0.01) and 1000 Hz (p < 0.05). The typical two-peak pattern of WBTA measurements was seen in both ears preoperatively but changed to a one-peak pattern in the newly implanted ear. The linear mixed model showed that not only the cochlear implantation in general but also the insertion through the round window compared to the cochleostomy leads to a decreased absorbance at 750 and 1000 Hz. Conclusions: With WBTA, we were able to detect mechanical changes of the acoustical pathway after CI surgery. The implantation of a CI led to decreased absorbance in the lower frequencies and the two-peak pattern was shifted to a one-peak pattern. The result of the linear mixed model indicates that WBTA can detect mechanical changes due to cochlear implantation not only in the middle ear but also in the inner ear.

Background/Objectives: Electrocochleography (ECochG) is a promising tool to monitor preservation of cochlear structures and function during cochlear implant (CI) surgery. However, the interpretation of ECochG signal changes during insertion of the CI electrode array remains controversial. This study investigates the influence of the degree and localization of cochlear trauma on ECochG signal changes using a mouse model. Methods: C57BL/6J-Crl1 mice underwent intracochlear ECochG recordings during the insertion of a platinum–iridium electrode. Results: In case of grade 1 and 2 cochlear trauma, as determined by post-mortem histological analysis, we found that a reduction in intracochlear cochlear microphonic (CM) amplitude correlates more significantly with the location of the trauma than with its severity. The more basally a trauma is located, the larger the CM amplitude drop. Furthermore, the results revealed that grade 1 or 2 trauma was detectable through ECochG before more severe trauma developed. Conclusions: These findings suggest that intracochlear ECochG can serve as a reliable intraoperative tool for detecting early and possibly reversible cochlear trauma, preventing more severe damage and aiding hearing preservation. The results emphasize the need for a nuanced interpretation of CM signal drops, considering trauma location and cochlear structure integrity at the site of trauma and apical to it.

Introduction: Recent advancements toward minimizing surgical trauma and preserving residual hearing during cochlear implantation have promoted the use of intracochlear electrocochleography (ECochG) for intraoperative surveillance. However, variations in the distribution of response generators throughout the cochlea complicate the interpretation of signal changes during electrode array insertion. This exploratory study aimed to investigate whether simultaneous recordings from 2 locations within the cochlea could address this issue. This was done by (1) comparing recordings acquired simultaneously from an apical and a more basal electrode contact during atraumatic electrode array insertions; and (2) comparing these response patterns with preoperative pure-tone audiograms. Materials and methods: In 10 standard CI recipients, ECochG recordings were obtained during stepwise insertion of a short-temporary electrode array. Simultaneous intracochlear recordings were acquired from 2 contacts separated by 4.2 mm in response to 500 Hz tone bursts. For both electrode contacts, the differences between responses to alternating-polarity stimuli, hereafter named “ECochG responses,” were derived. After completion of the recordings, the temporary electrode array was removed and a standard CI electrode array inserted. Results: In 6 of 10 participants, ECochG response amplitude decreases of ≥3 dB were recorded at the more basal electrode contact. In 4 cases, these amplitude drops were preceded by amplitude drops recorded at the apical electrode contact, with both occurring no more than 1.7 mm apart along the cochlear duct. Trauma would be expected to produce a simultaneous amplitude drop—at different recording locations—for both electrodes. In contrast, a drop at the basal electrode that is preceded by a drop in the ECochG recording at the apical electrode, with both drops occurring at approximately the same location, is likely atraumatic. These atraumatic drops may also be associated with large phase shifts. Overall, the ECochG response tracks recorded at the apical and more basal contact were similar, while the ECochG response patterns and audiogram did not show a strong resemblance. Conclusion: The proposed approach could facilitate the detection of ECochG response changes relevant for predicting hearing preservation during cochlear implantation. By distinguishing between simultaneous and sequential amplitude drops, this method could provide additional insights into the atraumatic nature of certain ECochG response changes.