Human round window: morphometry and topographical anatomy and their effect on cochlear implantation

Abstract

Background Renewal interest of round window (RW) approaches necessitates further acquaintance of its complex anatomy and its variations.Aim of work The aim of this work is to study the anatomical characteristics of human RW and the importance of variations in this anatomy to the process of cochlear implantation (CI).Materials and Methods Twenty human temporal bones were obtained from cadavers and preserved in formalin. Microdissection was done in two phases, phase 1 through facial recess approach and phase 2 external auditory canal approach after the tympanic membrane and ear ossicles were removed, the RW and OW areas were exposed, shape, height and width of the RW were noted. Its distances from OW was measured.Results Oval (60%), round (25%) and triangular (15%) shapes of RW were observed. The average height and width of the RW were 1.91 ± 0.78 mm and 1.37 ± 0.43 mm, respectively. There was a statistically significant correlation (r = 0.95, P < 0.001) between the height and width of RW. The distances between the RW and the OW was in the range of 1–3.5 mm. There were no statistically significant differences as regard to gender, or side. Electrode insertion could be challenging in cases where the height and width of the RW are <1 mm.Conclusion This information could be useful for selecting cochlear implant electrodes in order to avoid potential risks to vital neurovascular structures during implant surgery.