Temporal Bone Histopathology of First-Generation Cochlear Implant Electrode Translocation

To evaluate the histopathology of human temporal bones (HTBs) with cochlear implants (CI).

Understanding CI translocation injuries is critical for improving outcomes.

Thirteen HTBs from 12 CI patients were studied. Six HTBs exhibited translocation with localized injury (Group 1) and seven HTBs exhibited translocation with significant lateral wall injury (Group 2). There were no significant differences between Group 1 and Group 2 for age at death, age at implantation, and years with CI.

Four out of six of Group 1 had round window approach, while all seven of Group 2 had cochleostomy approach. Translocation injuries tended to occur near 180 degrees of angular insertion with a mean of 186.36 ± 51.62 degrees. Average CI insertion length for Group 2 was 21.86 ± 2.55 mm, significantly longer than Group 1 at 18.50 ± 3.33 mm (p = 0.031). Group 1 had an average of 17300 ± 9415 spiral ganglia neurons (SGNs) while Group 2 had significantly fewer SGNs 6714 ± 4269 (p = 0.015). Group 1 average auditory performance of 66.55 ± 27.20% was higher than that of Group 2 of 39.86 ± 15.36%. Group 2 had a high degree of osteoneogenesis and infiltration of cells generally localized to areas of translocation injury and cochleostomy.

Translocation injuries tend to occur at an insertion angle of 180 degrees, at 9 to 10 mm. Lateral wall injury and damage to the organ of Corti incites fibrosis, osteoneogenesis, and infiltration, lower SGN count and poorer auditory performance. Longer electrodes were more prone to translocation and higher chance of significant intracochlear injury.