A Soft-Surgery Approach to Minimize Hearing Damage Caused by the Insertion of a Cochlear Implant Electrode: A Guinea Pig Animal Model *Pietro Giordano, †Stavros Hatzopoulos, ‡Nadia Giarbini, †Silvano Prosser, §Joseph Petruccelli, *Edi Simoni, kChiara Faccioli, *Laura Astolfi, and kAlessandro Martini *Bioacoustics Research Laboratory, University of Padua, Padua; ÞDepartment of Audiology, University of Ferrara, Ferrara; þDepartment of ENT and Head-Neck Surgery, Meran; §Department of Mathematical Sciences, Worcester Polytechnic Institute, Worcester, Massachusetts, U.S.A.; and kENT Surgery, Department of Neurosciences, University of Padua, Padua, Italy Objective: A ‘‘soft surgery’’ technique was applied, using vari- ous types of specifically designed dummy electrodes, to mimic cochlear implantation in a guinea pig model, and the degree of hearing-preservation/cochlear damage was assessed. Methods: Tricolor guinea pigs were divided into 3 groups: group A were implanted with electrodes without any contacts or wires (soft electrode), group B were implanted with electrodes having a metallic wire inside (stiff electrode), and group C underwent a cochleostomy procedure without implantation. Compound action potentials, in the range of 4 to 32 kHz, were used to assess electrophysiologic changes in the hearing func- tion presurgery and postsurgery. Data were collected before surgery, at times t = 0 (immediately after surgery) and at 3, 7, 14, and 30 days. Results: At low frequencies (4Y8 kHz), an immediate elevation of hearing threshold was observed in all 3 groups. Higher threshold shifts were more consistent for group B implanted with a stiff electrode, in comparison to the other 2 groups. Animals from group C presented a recovery from hearing loss, starting 3 days after surgery. At high frequencies (16Y32 kHz), the elevation of hearing threshold was higher, as compared with the data from the low frequencies. Group C animals presented oscillatory threshold shifts twice, and the recovery to normal threshold values occurred approximately at t = 14 days. Conclusion: The data suggest that cochleostomy is minimally harmful to the inner ear and that a soft electrode might better preserve the inner ear integrity than a rigid electrode. Key Words: Auditory brainstem responseVCochlear implantVCompound action potentialVGuinea pigVResidual hearingVSoft surgery. Otol Neurotol 35:1440Y1445, 2014. Cochlear implantation (CI) has progressed considerably in recent years as highly advanced devices and surgery tech- niques offer a wide range of possibilities for the treatment of deafness. As a result, the criterion for cochlear implantation (CI) has shifted from a pure tone average (PTA) greater than 90 dB HL to a PTA greater than 70 dB HL and a selective loss on mid-to-high frequencies (1); even cases of mild to moderate loss (30Y55 dBHL) associated with auditory neuropathy are considered for CI (2). In these cases, the inner ear presents residual hearing; thus, it is very important to further develop CI techniques and materials that will minimally impact the cochlear mechanical integrity. The preservation of residual hearing is particularly important in cases of young children subjected to CI, and various nov- elties have been proposed in terms of stimulation modalities (3) or even electrode implementations using cochlear cells regeneration promoters (4,5). The mechanical trauma caused by the insertion of a CI electrode into the inner ear has been described with ani- mal models (6Y9). A number of studies on guinea pigs by Eastwood et al. (10), Chang et al. (11), and James et al. (12) have proved that after the placement of a dummy electrode in the basal turn of the scala tympani, the high- frequency hearing (24Y32 kHz) is compromised, with an immediate threshold shift of 40 dB. Ni et al. (13) found that the placement of a shorter electrode in the inner ear of Address correspondence and reprint requests to Nadia Giarbini, M.D., Ph.D., Department of ENT and Head-Neck Surgery, Meran, Italy; E-mail: nadia.giarbini@gmail.com Pietro Giordano, Silvano Prosser, Edi Simoni, Chiara Faccioli, Laura Astolfi, and Alessandro Martini received grants and support for travel from MED-EL and a grant from Cochlear Ltd. Nadia Giarbini served as a consultant for and received support for travel from MED-EL. Supplemental digital content is available in the text. Otology & Neurotology 35:1440Y1445 Ó 2014, Otology & Neurotology, Inc. 1440 Copyright © 2014 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.