A Micro-Computed Tomography Study of Round Window Anatomy and Implications for Atraumatic Cochlear Implant Insertion.

Abstract

The goal of this study was to interrogate high-resolution three-dimensional reconstructions of round window anatomy to illustrate and characterize structural variability with implications for atraumatic cochlear implant insertion. Cochlear implants are increasingly used to improve sound detection in patients with substantial residual hearing. However, traumatic cochlear implant insertion through the round window involving upward deviation of the electrode into the spiral ligament, basilar membrane, and osseous spiral lamina, medial impaction on the modiolus, or interscalar excursion into the scala vestibuli are associated with lower rates of hearing preservation and poorer speech perception.Successful atraumatic insertion is dependent on an anatomical understanding of the middle and inner ear. The round window bony niche lacks distinct demonstrable anatomical landmarks for the position of the round window membrane, and there is limited guidance on the amount of bony overhang that can be safely drilled away. A greater understanding of the anatomical variation around the round window could enhance treatment efficacy. Fourteen human cadaver temporal bones were imaged using microcomputed tomography. Resulting scans were digitally reconstructed, segmented, and measured. Round window niche walls vary substantially in size and projection. Round window average short diameter measured 1.30 mm (range 1.07-1.44), and is limited by the crista fenestrae at the inferoanterior margin of the round window. Crista fenestrae size and morphology varied considerably. Reconstructions with solid and translucent panels are presented. Anatomical heterogeneity should be considered in cochlear implant selection, drilling, and choice of insertion vector.