Yellur Kavitha - Department of ENT, SDM College of Medical Sciences and Hospital, SDM University, Dharwad, Karnataka, India.
Upendra Kumar Joish - Department of Radiology, SDM College of Medical Sciences and Hospital, SDM University, Dharwad, Karnataka, India.

Introduction: In morphologically normal-appearing inner ears, measurements of the distance between the round window and carotid canal (RCD), the maximum diameter of the basal turn of the cochlea next to the round window (BD), and the thickness of the promontory (PT) just lateral to the basal turn may be used as guide for safe cochleostomy and implant placement.Materials and Methods:From January to March ۲۰۲۲, a cross-sectional observational study was carried out in a tertiary care hospital. The round window to carotid canal distance (RCD), the largest diameter of the cochlea's basal turn next to the round window (BD), and the thickness of the promontory immediately lateral to the basal turn (PT) were measured using CT temporal bone images of ۱۵۰ persons without cochlear abnormalities. The values obtained were compared using Paired T-test for significance of difference between both genders and sides.Results:A total of ۱۵۰ participants—۷۵ men and ۷۵ women—with a mean age of ۳۷.۵ years were enrolled in the study. With a range of ۷.۱۸ mm to ۱۰.۵۲ mm, the mean RCD was ۸.۸۴ mm (SD ۰.۸ mm). The mean BD was ۲.۲۷ mm (SD ۰.۴ mm), while the mean PT was ۱.۱۵ mm (SD ۰. mm). The values obtained did not differ significantly in both the genders and the right and left sides (p = ۰.۳۷ and ۰.۲۴, respectively).Conclusion: The present study has defined and calculated pertinent measures at cochleostomy site that will aid safe electrode insertion and prevent misplacement.

Basal turn diameter, Cochlear Implantation, cochlear ossification, Round window to carotid canal distance, Promontory thickness