Time course of transimpedances is affected by cochlea implant surgical technique.

Abstract

Background: For cochlear implant (CI) users after subtotal cochlectomy for removal of intracochlear schwannomas, significantly different intracochlear potentials can be observed compared with cochleae of CI patients after round window electrode insertion. The time course of this difference after surgery is so far unknown.

Purpose: The change of intracochlear potentials over time and differences between surgical approaches are investigated.

Methods: In a retrospective study of cochlear implant recipients, the electrode transimpedances were measured and compared between 19 patients after subtotal cochlectomy and 20 patients after round window insertion. Transimpedances were measured with pulse widths of 37 µs and current units of 100 CL to 110 CL using a monopolar stimulation and recording mode (MP2). For each patient, at least three time points over a period of up to four years were used for time course analysis.

Results: The transimpedances of patients after subtotal cochlectomy were significantly smaller than those of the round window group. The largest transimpedance changes over time were observed for basal electrode contacts in patients after round window insertion.

Conclusions: For the interpretation of transimpedances, it is relevant to consider the time since surgery and the CI insertion technique. The width of the electric field may be related to loss of intracochlear conductive fluid due to surgical trauma and fibrotic processes.