The histopathology of revision cochlear implantation

The current study evaluates histopathologic changes in the temporal bones of 4 human subjects who underwent revision cochlear implantation. Specimens were removed at autopsy, fixed and prepared for histological study by standard techniques. Specimens were serially sectioned, reconstructed by two-dimensional methods, and the tracks of the initial and revision cochlear-implant electrodes identified. The tracks were of three types: a 'common track' (shared by the reimplantation electrode and initial electrode), 'two tracks' (where the reimplantation electrode was in a different track than that of the initial electrode) and 'one track' (where the reimplantation electrode extended beyond the initial electrode, forming a single track). Associated histopathologic findings (new bone formation, fibrosis or inflammatory cells, and cochlear fluid) were evaluated for the three types of tracks. In all 4 subjects, the insertion depth of the revision cochlear implant was deeper than that of the initial cochlear implant. The primary track of the initial implantation did not interfere with insertion of a revision cochlear implant, and the trajectory of the revision electrode did not always follow the primary track. In cochlear segments with a common track or two tracks, the mean (across-subject) percent area of the extraelectrode cochlear duct filled with abnormal (new bone or fibrotic) tissue (43.2%) was significantly greater than the mean percent area occupied by fluid (13.4%; t = 3.12, d.f. = 19.9, p = 0.003).