Cochlear implantation via the round window membrane minimizes trauma to cochlear structures: A histologically controlled insertion study

TLDR

The study aimed to assess cochlear implant trauma to intracochlear structures when inserting the electrode via the round window membrane. Eight fresh human temporal bones were histologically examined after electrode insertion using two array types, with a special fixation and embedding protocol allowing undecalcified bone sectioning and radiologic and histologic depth assessment. All arrays resided in the scala tympani, with basal trauma avoided in all but one specimen, a mean insertion depth of 382.5°, and only one case of apical trauma; thus round‑window insertion proved atraumatic and suitable for combined electric and acoustic stimulation.

Abstract

Objective To evaluate cochlear implant trauma to intracochlear structures when inserting the electrode via the round window membrane. Material and methods Eight fresh human temporal bones were evaluated histologically after insertion using two types of cochlear implant array. Bones underwent a special fixation and embedding procedure that allowed sectioning of undecalcified bone with the electrode in situ. Insertions depths were evaluated radiologically and histologically. Results All arrays were found in the scala tympani of the cochlea. Basal trauma could be avoided in all but one specimen. The mean depth of insertion was 382.5°. Apically, only one implanted bone showed cochlear trauma exceeding lifting of the basilar membrane. Conclusion Insertions through the round window membrane were shown to be atraumatic, even in basal cochlear regions. This route of insertion might be very effective for combined electric and acoustic stimulation of the auditory system.