Introduction:
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.
Methods:
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.
Results:
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.
Conclusion:
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.
