Progressive malfunction of hearing performance by CI electrode dislocation
23 April 2019 (online)
In case of complications after CI surgery a distinction is made between device errors and medical errors. Device errors are subclassified into 'hard failure' and 'soft failure'. A 'hard failure' is an explicit device defect, e.g. rupture of electrode. These kinds of errors can be diagnosed by an abnormal integrity test. 'Soft failure' is rare, here a device malfunction is suspected, which, however, cannot be detected with in vivo methods currently available.
A 60-year-old patient presented to us with progressive malfunction of speech understanding with her CI. In 2014 she was supplied with a MedEl® Concerto (Flex28) CI after sudden hearing loss. The postoperative control of the electrode position by rotation tomography showed a correct position. Since April 2018, the hearing performance with the CI decreased significantly.
The technical review showed slightly increasing impedances of the basal electrodes. Due to the integrity test, it was assumed that the electrodes 8 – 12 were outside the cochlea. Imaging by rotation tomography confirmed the suspected reason of the decreasing hearing performance. Five electrodes were dislocated from the cochlea. In revision surgery, the electrode carrier could be completely reinserted and fixed into the cochlea.
In progressive malfunction of the hearing performance, imaging should be performed to check the electrode position, especially with increasing impedances of the basal electrodes. In CI implantation with straight electrode carriers attention should be taken to ensure reliable fixation. This can be done with cement, for example. In curved near-modiolus electrodes, the risk of extracochlear electrode migration seems to be significantly lower.