Evaluation of Electrode-modiolus Distance and Cochlear Fibrosis Using Depth Sounding and Spectroscopy Tools

Evaluation of Electrode-modiolus Distance and Cochlear Fibrosis Using Depth Sounding and Spectroscopy Tools: Comparison With Postoperative Cone Beam CT

Cochlear fibrosis development can compromise the success and the outcomes of the cochlear implantation (CI) thus affecting the quality of life of the implanted patient. Correlating the results of the Transimpedance Matrix (TIM) measurements to the implant electrode location determined by the Cone Beam Computer Tomography (CBCT), this study aims to identify a range of TIM profiles within the implanted population, certain profiles suggesting the growth of the fibrosis tissue in cochlea

Fibrosis tissue growth after the CI is an inflammatory reaction to a foreign body occurring around the electrode array. It is considered responsible for a larger current diffusion, less precise stimulation of auditory nerve fibres and elevated electrical impedances thus affecting the functioning and the battery life of an implant. Fibrosis has been also proposed as a factor reducing residual hearing. Hence, its early detection and prevention can significantly improve the outcomes of CI.

To date, no reliable technique to visualise cochlear fibrosis in vivo exists. However, the TIM measurement developed by Cochlear® including depth sounding and spectroscopy tools could possibly provide a better "view" of the fibrosis apparition after CI. This approach has been already successfully applied in the University Hospital of Montpellier, France, to the patients-users of the Advanced Bionics cochlear implants.

One of the factors provoking the fibrosis tissue development is an electrode positioning into the scala vestibule (SV) versus scala tympani (ST). CBCT will be used to visualise the electrode location as well as possible damages of the inner ear caused by CI. The imaging data will be then linked to the TIM measurements results.

Potential participants will be recruited from the French population of the Cochlear® implant users either coming for their regular checks-up at the ENT service of the University Hospital of Montpellier and implanted for more than 6 month (time necessary for the fibrosis tissue to develop) or recently implanted at the same hospital.

For the patients with long-term implantation (160 participants planned) the TIM measurements will be performed only once whereas the newly implanted group (20 participants planned) will require these measurements to be repeated several times: on the day of the surgery as well as 15 days, 1 month, 2 months, 3 months and 6 months after it. For the first group the post operational CBCT imaging file will be extracted from the patient medical record; for the second group CBCT will be performed during the surgery.

The main objective of this study is:

For the group with long-term implantation - to show the difference in TIM profiles according to the electrode scala position (ST or SV) determined by CBCT 6 months or more after the implantation For the group with recent implantation - to evaluate the changes in TIM profiles with time according to the electrode scala position (ST or SV) determined by CBCT

The secondary objectives are common for both groups:

• To analyse various patient subgroups defined by the electrode type (Contour Advanced - only for long-term implantation, Slim Straight, Slim Modiolar) and the inner ear access (round window, enlarged round window or cochleostomy)
• To identify the TIM profile threshold values, potential indicators of the cochlear fibrosis apparition, depending on the electrode type
• To evaluate the depth sounding tool accuracy for the measurement of the distance between the electrode and the spiral ganglion in comparison to CBCT depending on the type of the electrode array.
• To evaluate the spectroscopy tool accuracy for fibrosis detection in specific cochlear areas (around electrodes dislocated to SV or basal electrodes in case of cohleostomy)

Inclusion Criteria:

Group with long-term implantation:

• Age18 years or older
• Affiliation to the French social security
• Signed and dated informed consent form
• Users of uni or bilateral cochlear implants for more than 6 months (CI24CA, CI422, CI512, CI522, CI532, CI612; CI622; CI632), in primo-implantation or reimplantation, with more than 18 electrodes active
• Postoperation CBCT imaging results available

Recently-implanted group:

• Age18 years or older
• Affiliation to the French social security
• Signed and dated informed consent form
• Indication for CI622 or CI632 cochlear implants
• Postoperation CBCT imaging results available

Exclusion Criteria:

• Vulnerable individuals (minors, adults protected in accordance to the French Public Health code, patients deprived of liberty by court decision)
• Daily usage of the cochlear implant for less than 4 hours or weekly usage for less than 5 days
• Failure or disfunction of the cochlear implant