Histopathologic assessment of fibrosis and new bone formation in implanted human temporal bones using 3D reconstruction

Abstract

Objective: To evaluate new bone formation and fibrosis in implanted human temporal bones and relate that to neurosensory elements preservation.

Study design: Human temporal bone histopathology study.

Setting: Temporal bone laboratory.

Subjects and methods: Ten human temporal bones from eight patients with multichannel cochlear implants and one single-electrode implant were examined under light microscopy and reconstructed with AMIRA 4.1 3D reconstruction software. Volumes of new bone formation, fibrosis, and patent area were calculated in each bone.

Results: The amount of fibrosis and new bone formation postimplantation varied among bones. There were no statistically significant relationships between age at implantation or duration of implantation and the overall amount of new tissue in the implanted ear. There was a relationship between total amount of new tissue and preservation of neurosensory elements only in segment I of the cochlea (Rho=-0.75, P<or=0.013). Most of the new tissue was located in segments I and II, segment III had little to no new tissue formation, and segment IV was clear in all of the subjects.

Conclusion: New tissue formation postimplantation was related to preservation of neurosensory elements primarily in segment I of the cochlea. In an era of hearing preservation surgery and hybrid cochlear implants, soft surgical techniques are advocated as a means to decrease surgical trauma.

Fig.1

(A) Segmentation according to Otte and Schuknecht. The midmodiolar line (broken line) is perpendicular to the section plane and divides the spiral ganglion into four segments. (B) Segmentation according to Linthicum. The midmodiolar section (broken line) divides the spiral ganglion into basal and upper turns.

Fig.2

Virtual three-dimensional reconstruction of one subject built using Amira 4.1. (blue) Normal tissue, represented by space filled with fluid. (white) Osteoneogenesis. (orange) Fibrosis. (green) Cochlear implant electrode.

Fig.3

Virtual cochlea sectioned into the four traditional segments of the spiral ganglion. (blue) Normal tissue, represented by space filled with fluid. (white) Osteoneogenesis. (orange) Fibrosis. (green) Cochlear implant electrode. Note that the scala vestibuli is healthy in segment I, yet in segment II it is filled with new tissue. This is due to the electrode being inserted in the scala tympani and breaking through to the scala vestibuli as it was moved into position.

Fig.4

Virtual cochlea sectioned into basal and apical turns. (blue) Normal tissue, represented by space filled with fluid. (white) Osteoneogenesis. (orange) Fibrosis. (green) Cochlear implant electrode. Note that most of the new tissue is located in the basal turn, where the implant is located.