Round window membrane insertion with perimodiolar cochlear implant electrodes.

Objective: The round window membrane (RWM) approach is designed to provide an atraumatic approach to scala tympani implantation with the goal of enhanced preservation of hearing and vestibular receptor function. Perimodiolar electrode designs offer advantages in electrophysiologic testing. However, perimodiolar arrays have only been investigated in insertion trials using temporal bone material. The aim of the present study was to evaluate perimodiolar electrode placement in a clinical trial.
Materials and Methods: The prospective nonrandomized study included 27 patients (October 2010 to February 2011). Due to the RWM approach, cochlear implantation electrode insertion was performed using a perimodiolar electrode array fitted with a stylet that enables movement through the first cochlear turn by withdrawing the stylet. We judged the feasibility of RWM approaches with perimodiolar electrodes and the electrode placement using flat panel detector radiography. Hearing preservation, vestibular receptor function (vestibular evoked myogenic potentials, subjective haptic vertical, and caloric irrigation), and subjective vertigo were evaluated in all RWM approaches.
Results: For anatomic reasons, RWM insertions were possible in 21 cases (78%). The basilar membrane disruption rate was 19% in RWM insertions using perimodiolar electrodes. In those patients with the electrode position within the scala tympani, vestibular receptor functions and subjective vertigo remained unchanged. The residual hearing preservation was unsatisfactory. The mean pure-tone average loss was 21 dB.
Conclusion: We believe that if performed regularly, the RWM insertion technique has almost no negative effects on vestibular receptor function and produces no vertigo. However, cochlear hair cells may be more sensitive to electrode insertion traumas than vestibular receptor cells. The use of perimodiolar electrodes may require more atraumatic electrodes to achieve hearing preservation.