Surgical trauma after sequential insertion of intracochlear catheters and electrode arrays (a histologic study)

To evaluate histologically the risk of trauma to intracochlear structures after sequential insertion of an intracochlear catheter and an electrode array. A previous computed tomographic scan-based study demonstrated that introduction of a flexible disposable intracochlear catheter for drug delivery to a distance of up to 15 mm was feasible and showed no radiologic evidence of basilar membrane trauma. Fifteen fresh human temporal bones were prepared for cochlear implantation. We sequentially performed the introduction of the catheter, the injection of 15 µl of an iodine solution into the scala tympani via the catheter, and the removal of the catheter in 14 temporal bones, and finally, 2 types of electrode array (Flex EAS and Flex Soft) from MED-EL, were inserted into 10 temporal bones. The bones were fixed and embedded in methylmethacrylate to cut the undecalcified temporal bones parallel to the modiolus axis with the electrode array in place, and each histologic section was photographed to document the location and extent of trauma in the cochlea. No specific damage (Grade 0 trauma) to cochlear structures occurred in 12 temporal bones, and elevation of basilar membrane (Grade 1 trauma) occurred in 2 cases. The electrode array was positioned in the scala tympani under the basilar membrane in all temporal bones, with one exception, in which the Flex Soft electrode array deviated behind the spiral ligament and into the scala vestibuli apically (Grade 3 trauma). The infusion of an iodine solution within an intracochlear catheter and the subsequent insertion of an electrode array was shown to be feasible and often atraumatic.