Surgical aspects of cochlear implantation: mechanisms of insertional trauma.

The development of hybrid electroacoustic devices has made conservation of residual hearing an important goal in cochlear implant surgery. Our laboratory has recently conducted anatomical studies directed toward better understanding mechanisms underlying loss of residual hearing associated with electrode insertion. This paper provides an overview of observations based on microdissection, scanning electron microscopy and temporal bone histology relating to inner ear injury that may occur during implant surgery. Trauma to cochlear structures including lateral wall tissues, the basilar membrane, the osseous spiral lamina and the modiolus is considered in relation to the implications of specific types of injury for hearing preservation. These findings are relevant to the design of future implant devices and to various important issues regarding the surgical technique used for implantation, including the possible use of the round window as a portal of entry for electrode insertion.