Cochlear implantation (CI) is a major treatment for inner ear deafness. We have recently performed the procedure in cases with labyrinthitis or ossified cochleas, which were previously considered as contraindications, because it is now possible to assess cochlear ossification by high-performance CT and also assess the cavities of the cochlea by three-dimensional MRI. We encountered 9 adult cases of ossified cochleas detected intraoperatively, and assessed the auditory thresholds and speech recognition scores (word and sentence) according to the grades and causes of ossification in these cases.
We performed CI surgery in 370 adult cases from 1985 to 2014, and found ossified cochleas in 9 of the 370 patients (2.4%; male:female, 4:5). We classified the 9 cases into grade I or grade II, depending on the extent of ossification of the cochlea, and into a group with deafness caused by meningitis or another with deafness of other causes, depending on the cause of the deafness. We compared speech recognition among all the groups. In the comparisons in the groups classified by the extent of ossification, the mean auditory threshold was 35.0 dB in the grade I group, and 33.6 dB in the grade II group; the mean word recognition score (WRS) was 38.0% in the grade I group, and 71.0% in the grade II group; the mean sentence recognition score (SRS) was 35.0% in the grade I group, while it was 72.4% in the grade II group. While no significant difference was apparent in the auditory threshold between the two groups, the WRS and SRS were better in the grade II group than in the grade I group. In the comparison of the groups classified according to the cause of ossification, the mean auditory threshold in the group with deafness secondary to meningitis was 44.5 dB, while that in the group with deafness secondary to other causes was 26.0 dB. The mean WRS/SRS in the two groups were 18.8%/19.5% and 86.4%/84.8%, respectively. Thus, all of the auditory threshold, WRS and SRS were significantly better in the group with deafness secondary to other causes than in the group with deafness secondary to meningitis. These results may be attributable to the small number of residual spinal ganglion cells in the cochleas in cases of deafness associated with meningitis or labyrinthitis. We expect good speech recognition after CI in cases with suspected cochlear ossification, based on the imaging findings, without meningitis or otitis interna.
