Analysis of Factors Affecting Hearing Preservation after Cochlear Implantation

Abstract

It is generally accepted that cochlear implants (CI) may be offered to individuals who have little potential for speech understanding, due to the limited benefits of acoustic stimulation using a well-fitted HA, although the definition of ‘limited benefits’ has been altered many times over the last twenty years. Originally, only those patients who had very little residual hearing and who showed no demonstration of sound awareness using HAs were considered to be candidates for cochlear implantation. Gradually, the criteria for implantation have been expanded to include patients with residual hearing (Di Nardo et al., 2007). This change in the criteria of qualification was supported by the observation that implanted patients performed better than individuals who used HAs and had comparable hearing loss. The opinion that preservation of any residual hearing must be an aim of all CI surgery has recently been expressed by authors reporting on the use of combined electric acoustic stimulation (EAS) (Skarzynski et al., 2007; James at al., 2005). Although preservation of hearing has been extensively reported, there are large individual differences in the degree of hearing loss after cochlear implantation (Skarzynski et al., 2002; Kiefer et al., 2004; James et al., 2005). Cochlear implantation may introduce damage to functional cochlear structures of inner ear and cause subsequent degeneration of neural tissue. Electrode insertion has the potential to trigger several mechanisms of cell death, including necrosis and different forms of programmed cell death (apoptosis). Therefore hearing preservation achieved after cochlear implantation may be influenced by a number of factors related to the demographic characteristic of the sample, electrode design or surgical technique. Factors influencing the preservation of residual hearing following cochlear implantation or reimplantation are still a matter of debate.