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BACKGROUND

In rare cases, a cochlear implantation can lead to a so-called tip fold-over during insertion of the electrode array. In order to detect or exclude such a misalignment a radiological check of the cochlear implant (CI) electrode array is carried out intra- or often post-operatively (gold standard), thereby exposing the patient to additional radiation. Alternatively, successful electrode insertion can be verified by measuring the spread of excitation (SOE). However, interpretation of the test results requires considerable expertise, and standardized measurement protocols and reference values are also essential. Therefore, the aim of the study is to evaluate an automated screening procedure in order to obtain a reliable statement about the normal tonotopic position of the implanted CI electrode array intraoperatively and with as little effort as possible.

METHODS

For CI surgery with Cochlear™ Nucleus® implants, an intraoperative tip-fold-over (TFO) screening was performed in a bi-centric study in over 100 adult patients: Firstly, threshold measurements for electrically evoked compound action potential (ECAP) using AutoNRT™ were recorded. Subsequently, SOE measurements were carried out on electrodes 13 and 22. The automated evaluation of the SOE data sets then made it possible to make a dichotomous decision about a normal or abnormal test result. The position of the electrode array was checked intra- or post-operatively using conventional transorbital X-ray (reference method).

RESULTS

The intraoperative TFO screening procedure is applicable in around 80% of cases. The accuracy of the screening for measurements via the active stimulation electrodes 13 / 22 is 63.9% / 95.4%. The classification error is 36.1% / 4.6% and the phi coefficient is 0.27 / 0.69. All radiologically proven tip-fold-overs were reliably identified with the intraoperative screening (sensitivity = 100%). A higher specificity (>95%) can be achieved only with measurements via electrode 22.

CONCLUSIONS

The TFO Screening via measurement at electrode 22 can successfully distinguish between a correct and incorrect position of the electrode array due to a tip-fold-over, and the remaining cases would require further imaging.