Histopathologic Analysis of Temporal Bones With Otosclerosis Following Cochlear Implantation

Abstract

Objective: Analyze changes in osteoneogenesis and fibrosis following cochlear implant (CI) surgery in patients with otosclerosis and compare differences based on insertion technique.

Background: When advanced otosclerotic disease extends to the otic capsule, severe and profound sensorineural hearing loss necessitates consideration of a cochlear implant. Histopathological analysis of the human temporal bone after implantation in the patient with otosclerosis may reveal important variables that predict CI success.

Methods: Histopathological evaluation of archival human temporal bones from subjects with a history of CI for cochlear otosclerosis. A total of 17 human temporal bones (HTB) were analyzed, 13 implanted, and 4 contralateral non-implanted controls.

Results: Histopathological studies revealed extensive osteoneogenesis and fibrosis which was more prominent at the cochleostomy insertion site in the basal turn of the cochlea often obliterating the scala tympani in the basal turn, and in some cases extending to the scala media and scala vestibuli. Cochlear hydrops was nearly universal in these cases. This contrasted with the round window insertion, which exhibited minimal osteoneogenesis within the cochlear duct. In addition, in the contralateral, unimplanted control ears, there was otosclerosis at the stapes footplate, fissula ante fenestrum but no osteoneogenesis within the cochlear duct.

Conclusion: Cochleostomy approach to CI insertion in otosclerosis patients is associated with significant fibrosis, osteoneogenesis, and cochlear hydrops. A round window insertion technique can be utilized to help minimize these histopathologic findings whenever feasible.

Figure 1:. 1a&b: Right cochlear implant via cochleostomy with a House/3M 6mm single-channel electrode (HTB 3, H&E stain).

67-year-old male with otosclerosis with cochlear implantation 2 years prior via cochleostomy. 1a. Electrode insertion path via cochleostomy (long, thin arrow) with surrounding extensive osteoneogenesis (short, thick arrow) extending throughout the scala tympani, with near obliteration at the basal turn. 1b. Midmodiolar view of same ear showing fibrosis along the path of the electrode in the scala tympani (star) and otoscelorosis plaques along the modiolus (arrow). 1c&d: Cochlear implantation via Round Window Approach with a House/3M 6mm single-channel electrode (HTB 8, H&E stain). 74 year-old male with a long history of otosclerosis who underwent left-sided cochlear implantation via round window approach. 1c. The insertion site of the electrode via the round window (star) shows minimal reactive tissue formation and very little neo-ossification. The crista fenestra is intact and the scala tympani patent despite a thin fibrous capsule along the length of the electrode. There is a small foci of otosclerosis (arrow). 1d. Cross-sectional view of the cochlea with further demonstration of electrode path with some surrounding osteogenesis (arrow). Magnification bar is 500 microns.

Figure 2:. Figure 2a&b: Cochlear implantation via cochleostomy with a House/3M 6mm single-channel electrode (HTB 9, H&E stain):

92 year-old female with a long history of otosclerosis who underwent right-sided cochlear implantation 10 years prior via cochleostomy insertion. 2a. The cochleostomy site shows extensive fibrosis and scarring around a large otosclerosis plaque (short arrow) near the basal turn. Surrounding the path of the electrode (long arrow) is intracochlear new bone formation (star) causing obliteration of the sinus tympani and of the scala media. 2b. Midmodiolar view of same ear showing a patent scala tympani (star) though present otoscelorosis plaques along the modiolus (arrow). 2c&d: Contralateral, non-implanted (HTB 14, H&E stain). 2c. Moderately-severe cochlear otosclerosis, with an intense focus along the basal turn of the cochlea (arrow). However, the scala appear patent throughout and there is no intracochlear new bone formation. 2d. Basal turn of the cochlea showing an intense focus along the basal turn and at the round window (arrow). Magnification bar is 500 microns.

Figure 3:. Cochlear implantation via cochleostomy with a House/3M 6 mm single-channel electrode (HTB 16, H&E stain):

Figure 3a: 58 year-old female with a history of streptomycin ototoxicity. There is mild fibrous tissue throughout the scala tympani (star) with surrounding areas of new bone formation along the periphery. There is additional fibrous tissue extending into the scala media and scala vestibuli. 3b. Cochlear implantation via Round Window Approach with a House/3M 6mm single-channel electrode (HTB 17, H&E stain). 80 year-old male with a previous history of progressive SNHL spanning the previous 40 years who underwent a left-sided cochlear implantation 8 years prior via round window insertion. Mild fibrous tissue around insertion site with some loose areolar fibrous tissue in the scala tympani in the inferior basal turn extending only half way the length of the inferior basal turn. Magnification bars is 500 microns.