The Nucleus 532 Electrode: Intracochlear Position and Preservation of Residual Hearing

The Cochlear Nucleus 532 is a cochlear implant system with a potentially less traumatic electrode design because of its’ dimensions and perimodiolar position further away from the basilar membrane than midscalar or lateral wall electrodes. The manufacturer stated this electrode may be inserted through a cochleostomy, round window, or extended round window approach. We evaluated potential tip fold-over, electrode position within the cochlea with a per-operative Cone Beam CT-scan, and investigated the influence of electrode position on electrophysiological and audiometric outcomes.

Participants were 25 adults, unilaterally implanted with the CI532 electrode. One surgeon implanted all participant; 23 using the cochleostomy technique, and two participants using the extended round window approach. Electrode position was per-operatively visualised with fluoroscopy using flatpanel rotational CBCT scanner (Artis Zeego, Siemens). The high resolution images were analyzed post-operatively, for the exact position of the electrode contacts. Impedances, voltage distribution measurements, neural response telemetry and pre- and postoperative hearing thresholds were evaluated.

Preliminary results show that in one participant a tip fold-over occurred and in eight participants a translocation to the scala vestibuli occurred immediately distal to the cochleostomy. Average loss of residual hearing was significantly greater in participants with translocation than in participants without translocation. Respectively, average loss of three-frequency pure tone average (500, 1000 and 2000Hz) was 20.74dB and 5.33dB (p=0.016) and average loss of four-frequency pure tone average (500, 1000, 2000 and 4000Hz) was 19.72dB and 4.92dB (p=0.015). Further analysis of electrodes’ positions, and correlation with the electrophysiological and audiometric outcomes will be presented.