MSc SS Thesis Presentation

Detecting Electrode Array Tip Fold-over in Cochlear Implantation

Juriaan van der Graaf

In cochlear implantation surgery, the appropriate placement of the electrode array into the cochlea is vital. Suboptimal placement of the electrode array may lead to reduced hearing performance and speech recognition after the surgery. Currently, there are methods to confirm the electrode position post-operatively (e.g. through a CT scan), but it is not possible to monitor the insertion intra-operatively. This, combined with the fact that there is difference in surgical precision and insertion technique between surgeons, leads to great variability in electrode placement and in some cases to electrode malpositioning issues. One of the more problematic issues that may arise is folding of the electrode tip. Folding of the tip causes the electrode array to not reach deep enough into the cochlea, and it is likely to cause trauma due to the increased pressure on cochlear walls and membranes. On top of that, you effectively have “less” contacts to work with because contacts can be positioned very close to eachother due to the folding. Folding of the electrode array also disrupts the tonotopic organization of the cochlear implant (the contacts near the end of the array no longer correspond to the lowest frequencies). The effectivity of the treatment is thus reduced in patients with tip fold-overs. However, many modern day cochlear implants possess telemetry features. These are primarily used to check the implant’s proper functioning, but may also be helpful in monitoring the insertion of the electrode array. The telemetry features of a cochlear implant make it possible to measure the intracochlear electrical potential. The measured current spread is related to the electrode array’s shape and position, and thus may provide a way to detect folding of the tip. This can be done post-operatively, but can possibly also be done intra-operatively to monitor the insertion in real time. This application could be a useful tool to aid surgeons and clinicians. When used post-operatively, it may provide a cost-free method to detect tip fold-over. When used intra-operatively, it may provide a way to detect and prevent both fold-over and trauma to the cochlea.

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