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Objectives: To test the hypothesis that bipolar electrical impedance measurements in perimodiolar cochlear implants (CIs) may be used to differentiate between perimodiolar insertion technique favoring proximity to the modiolus or lateral wall., Study Design and Methods: Bipolar impedances are a measure of electrical resistance between pairs of electrode contacts in a CI. Stimulation is through biphasic pulses at fixed frequency. Impedance measurements were made in real time through sequential sampling of electrode pairs. Perimodiolar electrodes were inserted in temporal bones using one of two techniques: 1) In the standard insertion technique (SIT), the electrode array slides along the lateral wall during insertion. 2) In the Advance Off Stylet (Cochlear Ltd. Sydney) technique (AOS), the electrode maintains modiolar contact throughout the insertion process. A set of 22 insertions were performed in temporal bone specimens using perimodiolar electrode arrays with both AOS and SIT. Buffered saline was used as a substitute for natural perilymph based on similar electrical conductivity properties. Impedance with and without stylet removal were recorded with a 30-second sampling window at final insertion depth., Results: There is a significant difference in bipolar impedance measures between AOS and SIT, with impedances rising in measurements with stylet removal. Evaluation was based on two-sided analysis of variance considering technique and electrode with P < 0.025., Conclusion: Bipolar electrical impedance can be used to detect relative motion toward the modiolus inside the cochlea. This detection method has the potential to optimize intraoperative placement of perimodiolar electrode arrays during implantation. We anticipate that this will result in lower excitation thresholds and improved hearing outcome., Level of Evidence: NA. Laryngoscope, 127:1413-1419, 2017., (© 2016 The American Laryngological, Rhinological and Otological Society, Inc.)

Objective: Minimally invasive image-guided cochlear implantation (CI) utilizes a patient-customized microstereotactic frame to access the cochlea via a single drill-pass. We investigate the average force and trauma associated with the insertion of lateral wall CI electrodes using this technique., Study Design: Assessment using cadaveric temporal bones., Setting: Laboratory setup., Subjects and Methods: Microstereotactic frames for 6 fresh cadaveric temporal bones were built using CT scans to determine an optimal drill path following which drilling was performed. CI electrodes were inserted using surgical forceps to manually advance the CI electrode array, via the drilled tunnel, into the cochlea. Forces were recorded using a 6-axis load sensor placed under the temporal bone during the insertion of lateral wall electrode arrays (2 each of Nucleus CI422, MED-EL standard, and modified MED-EL electrodes with stiffeners). Tissue histology was performed by microdissection of the otic capsule and apical photo documentation of electrode position and intracochlear tissue., Results: After drilling, CT scanning demonstrated successful access to cochlea in all 6 bones. Average insertion forces ranged from 0.009 to 0.078 N. Peak forces were in the range of 0.056 to 0.469 N. Tissue histology showed complete scala tympani insertion in 5 specimens and scala vestibuli insertion in the remaining specimen with depth of insertion ranging from 360° to 600°. No intracochlear trauma was identified., Conclusion: The use of lateral wall electrodes with the minimally invasive image-guided CI approach was associated with insertion forces comparable to traditional CI surgery. Deep insertions were obtained without identifiable trauma.