variability of the cochlea & implant position

The knowledge of cochlear microanatomy is essential for atraumatic cochlear implantation. One recent focus of our laboratory is the analysis of the microanatomy of the human cochlea, particularly in relation to the position of the cochlear implant. Functional studies with investigation of the consequences of cochlear implantation are performed in animals.

A project in collaboration with the Advanced Bionics European Research Center investigated the variability of the human cochlea using µCT and 3D reconstruction using custom made MatLab procedures (Avci et al., 2014). This approach revealed an extensive variability of the microanatomy of the human cochlea in the range of ~ 25%. We have suggested a method to derive the length of the cochlea from clinical CT images obtained in patients. This may in the future lead to an individualized cochlear implantation, where the size of the implant is selected based on the individual size of the cochlea.

In a follow-up study, we could demonstrate that individual shape of the cochlea affects forces exerted on the cochlea during cochlear implantation (Avci et al., 2017). Furthermore, we observed a relation of these forces with cochlear trauma. While both these relations have been assumed in the past, in collaboration with the Advanced Bionics European Research Center, Hannover, we could provide evidence base for this theory. Given these circumstances it appears essential to image the cochlea of the subject prior cochlear implantation. The ENT clinics in Hannover adopted this approach for some time already, and we hope that other centers will follow to provide optimal outcomes, particularly in residually-hearing ears. Using the recently developed analytical models of the human cochlea (Pietsch et al., 2017 and Schurzig et al., 2021) should further improve the outcomes.

In studies in animals we investigated the reaction of the tissue to the cochlear implant and how much is this related to hearing loss and cochlear trauma. We could demonstrate that the sealing technique around the cochlear implant may significantly influence the tissue reaction and residual hearing (Burghard et al., 2014). Implantation through the round window and soft sealing techniques lead to best results.

Other histological techniques at our institute allow to investigate the microanatomy of the implanted cochlea: Peter Erfurt established and further developed a grinding technique that allows to visualize the location of the implant within the cochlea at a microscopic dimension (see figure below) and use of confocal laser scanning microscopy in the lab of Prof. G. Reuter at our institute, allows to visualize the guinea pig cochlea in 3D in excellent condition (Wrseszcz et al, 2013, see figure right).


Guinea pig cochlea in the confocal laser scanning microscopic analysis, taken from Wrseszcz et al., 2013.

Left: The largest and the smallest human scala tympani of our sample.  Both the length as well as the width/height of the cochleae are very different. Taken from Avci et al., 2014.  Right: 3D reconstruction of an implanted guinea pig cochlea using the grinding technique. Scala tympani is shown in red, implant in blue. The implant is located in the   basalmost halfturn of the cochlea. Data from Burghard et al., 2014, 3D reconstruction by Dr. Peter Baumhoff.

Different force profiles during cochlear implantation depending on the insertion direction. Insertion along the lateral wall generated smoother force increase during implantation. Figure from Avci et al., 2017.

Examples of the grinding technique refined by P. Erfurt at the Institute of AudioNeuro-Technology. The figures show the microstructure of the human cochlea and the location of the implanted electrode.