[Surgery and electroneurophysiological evaluation for CI case with modiolus ossification]

The purpose of this study is to report surgical skills for CI cases with modiolus ossification and to investigate the relation between post-operational electroneurophysilogical test result and speech recognition result. Further more, we also attempt to confirm indications for CI in this specific population.

Based on temporal bone HRCT, 7 subjects were identified as modiolus ossification from 101 cases with cochlear ossification. Modiolus ossification is confirmed by CT scan if CT value in modiolus reaches or exceeds 900 HU with the exception of congenital modiolus ossification or modiolus seal off. Electroneurophysiological test was conducted intra- and pos-operationally speech tests were applied for 7 subjects.

Normal impedance value was observed by intro-operational measurement in 7 subjects. EABR test was conducted and negtive response was observed in only 1 subject, while other 6 subjects were confirmed with atypical EABR waves which were observed in apical and middle turn region. Hearing threshold test (in sound field) was applied, no auditory response was recorded for the subject without EABR waveform, while hearing threshold in average for the other 6 subjects was 75 dB. Results of speech tests (Mandarin) were followed as 0 for the one without EABR wave, while 100% (simple finals test) and 30% (simple initials test) for the other 6 subjects.

Optimal multichannel CI surgery that inserting and locating electrode array spirally is very frequently interrupted by ossification,which was indentified with atypical EABR wave and relative poor speech recognition results, especially in modiolus ossification case. A post-operative negative EABR response may indicate surgical failure following cochlear implantation.