Micro-CT scan, electron microscopy and optical microscopy study of insertional traumas of cochlear implants

Knowledge of cochlear trauma resulting from the implantation of electrodes is important for the development of atraumatic surgical techniques. The purpose of this study was to demonstrate the advantages of micro-CT scanning, back-scattered electron microscopy (BSEM) and optical microscopy (OM) in understanding the mechanisms of cochlear trauma due to cochlear implantation.

Our study involved six petrous bones removed from fresh human cadavers: one control specimen plus five other specimens that were surgically implanted with Neurelec Digisonic SP EVO electrode arrays. All six specimens underwent glycol methyl methacrylate embedding, were examined via micro-CT scan and were then sectioned for histological analysis of undecalcified samples via BSEM and OM.

The 2D micro-CT scan reconstructions did not display cochlear microtrauma due to a limited resolution and the loss of information caused by the metallic artifacts of the intracochlear electrodes. The 3D reconstructions displayed the quality of the electrode array positioning in the cochlea and enabled determining the axes on which to section the specimens for histological examination. BSEM afforded a clear view of the damage to the osseous structures of the cochlea, but did not display the soft tissue injuries. OM enabled viewing and grading the histological lesions resulting from insertion.

In our opinion, the combination of 3D micro-CT scan reconstructions and histological analysis using OM appears to be the best method to analyze this type of trauma.