Single-incision cochlear implantation and hearing evaluation in piglets and minipigs

Objectives: Various animal models have been established and applied in hearing research. In the explo-ration of novel cochlear implant developments, mainly rodents have been used. Despite their important contribution to the understanding of auditory function, translation of experimental observations from ro-dents to humans is limited due to the size differences and genetic variability. Large animal models with better representation of the human cochlea are sparse. For this reason, we evaluated domestic piglets and Aachen minipigs for the suitability as a cochlear implantation animal model with commercially available cochlear implants.Methods: Four domestic piglets (two male and two female) and six Aachen minipigs were implanted with either MED-EL Flex24 or Flex20 cochlear implants respectively, after a step-by-step surgical approach was trained with pig cadavers. Electrophysiological measurements were performed before, during and after implantation for as long as 56 days after surgery. Auditory brainstem responses, electrocochleography as well as electrically and acoustically evoked compound action potentials were recorded. Selected cochleae were further analyzed histologically or with micro-CT imaging.Results: A surgical approach was established using a retroauricular single incision. Baseline auditory thresholds were 27 +/- 3 dB sound pressure level (SPL; auditory brainstem click responses, mean +/- stan-dard error of the mean) and ranged between 30 and 80 dB SPL in frequency-specific responses (0.5 - 32 kHz). Follow-up measurements revealed deafness within the first two weeks after surgery, but some animals partially recovered to a hearing threshold of 80 dB SPL in certain frequencies as well as in click responses. Electrically evoked compound action potential thresholds increased within the first week after surgery, which led to lower stimulation responses or increase of necessary charge input. Immune re-actions and consecutive scalar fibrosis following implantation were confirmed with histological analysis of implanted cochleae and may result in increased impedances. A three-dimensional minipig micro-CT segmentation revealed cochlear volumetric data similar to human inner ear dimensions.Conclusions: This study underlines the feasibility of cochlear implantation with clinically used cochlear implants in a large animal model with representative inner ear dimensions comparable to humans. To bridge the gap between small animal models and humans in translational research and to account for

Automated summary

This study evaluated the suitability of domestic piglets and Aachen minipigs as a cochlear implantation animal model with commercially available cochlear implants. The results showed that these animal models have inner ear dimensions comparable to humans and can be used for implantation surgery with clinically used cochlear implants.