Round Window Insertion of Precurved Electrodes Is Traumatic

Objective: Assess endocochlear trauma by adjusting: 1) location of cochleostomy or round window insertion, and 2) size of precontoured electrode array. Study Design: Cadaveric temporal bone study. Methods: Locations of electrode placement into the cochlea were as follows: 1) round window, 2) anterior inferior to the round window, 3) anterior inferior to the round window niche, 4) superior to the round window niche. Two types of electrode arrays were used: a larger precontoured electrode and thinner pre-curved research electrode. Histologic sections were made by a blinded third party. Results: Fourteen bones were included in the study. Six (42.8%) of the bones were right ears. Seven bones had no endocochlear trauma. Seven bones have intracochlear trauma. Round window insertions had a high incidence of intracochlear trauma with precontoured electrodes (3/4 bones). Superior cochleostomies with electrode placement had significant intracochlear trauma (2/2 bones). Insertions made anterior inferior to the round window annulus had a 50% incidence of intracochlear trauma (2/4 bones). No endocochlear trauma observed for insertions through traditional cochleostomies (4/4 bones). Less endocochlear trauma was observed with the thinner electrode: 57% versus 42% in the larger electrode array. A higher incidence of tip fold-over was observed with the thinner electrode array (2/7 electrodes). No tip fold-over was noted in the larger electrode. Conclusion: The traditional cochleostomy had the least incidence of endocochlear trauma. The smaller electrode array did not significantly affect the incidence of endocochlear trauma, but the thinner array had a higher incidence of tip fold-over, which caused trauma distally.