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Keywords:

  • Cochlear implant;
  • perimodiolar electrode;
  • intraoperative electrical auditory brainstem response

Abstract

Objective/Hypothesis Positioning intracochlear electrodes adjacent to the modiolus would lead to a reduction in threshold levels and latencies, as measured with electrically evoked auditory brainstems responses. Recently, Cochlear Corporation introduced a new perimodiolar array (Contour electrode) characterized by a platinum stylet inserted into the array's silicone carrier that keeps the electrode in a straightened configuration before insertion. After completion of the insertion, the withdrawal of the stylet allows the array to coil within the cochlea positioning electrodes closer to the modiolus. The purpose of the study was to analyze the stimulation properties of the Contour electrode by evaluating the effects of the withdrawal of the stylet on electrical auditory brainstem response (EABR) characteristics.

Methods Electrical auditory brainstem response registrations were performed intraoperatively on three electrodes (1 apical, 1 medial, 1 basal) before and after the removal of the stylet in 10 patients implanted with the Nucleus 24 Contour device. A within-patient comparison of EABR characteristics was performed. The Student t test was used to assess differences in EABR measures obtained before and after the stylet removal.

Results Mean EABR thresholds were significantly lower after the removal of the stylet than with the stylet in situ for all three electrodes tested. After the removal of the stylet, latencies of waves III and V significantly decreased, whereas amplitudes significantly increased.

Conclusion Reduction in EABR threshold levels and latencies as well as an increase in waves III and V amplitudes after the stylet removal all demonstrate the effectiveness of the Contour system in positioning intracochlear electrodes closer to auditory neurons.