Early Elevation and Normalization of Electrode Impedance in Patients with Enlarged Vestibular Aqueduct Undergoing Cochlear Implantation.

OBJECTIVE:To characterize early changes in impedance in patients undergoing cochlear implantation with and without enlarged vestibular aqueducts (EVA).METHODS:Case-control retrospective study of patients undergoing cochlear implantation with and without EVA. Impedance was measured across all channels intraoperatively and within 24 hours of surgery. All patients received the same electrode array.RESULTS:Ten patients with EVA (and matched controls were identified). The average intraoperative impedance across all electrodes was significantly higher in patients with EVA (13.1 ± 1.4 kΩ) than in controls (9.6 ± 2.5 kΩ, p  < 0.001). At 24-hour activation, the average impedance across all electrodes was roughly equal in both groups (6.8 ± 2.7 kΩ versus 6.5 ± 2.1 kΩ, p  = 0.72).CONCLUSIONS:This study is the first identify differences in intraoperative impedance between patients with and without EVA. In addition, these data demonstrate rapid normalization within 24 hours of surgery. Such findings can give a window of insight into both the intracochlear microenvironment of patients with EVA and the important early electrode-fluid-tissue interface changes that occur within hours of surgery for all patients.