Temporal bone histopathology study on cochlear otosclerosis: A memoir for the cochlear implant surgeon

The aim of this study was to describe the pathologic changes in temporal bones with cochlear otosclerosis that may have implications for cochlear implantation. Fifteen human temporal bones with otosclerosis were used for this study. In each temporal bone was studied: (1) medial wall of the middle ear and in particular the horizontal segment of the facial nerve canal; (2) the round window niche and the corresponding part of the scala tympani; (3) the area of the labyrinthine segment and first genu of the facial nerve. Six temporal bones revealed otosclerotic pathology spanning the otic capsule between the cochlear endosteum and the facial nerve canal. The labyrinthine facial nerve was enveloped by otosclerosis in two cases, while the horizontal segment was involved in four temporal bones. Complete obstruction of the round window niche was observed in three cases, while round window niche obstruction was observed in four temporal bones. Otosclerosis presents difficulties for implant candidates. These otosclerotic changes with obstruction are usually present at the round window or at the scala tympani. The histology described underpins the need to counsel patients regarding the possibility of facial nerve stimulation and difficult implantation. Key words: Cochlear otosclerosis, histopathology, round window, obstruction.