Measuring cochlear duct length in North Indian population: a detailed study

Abstract

Background: The cochlea is a shell-like structure of the inner ear which is comprised of two canals (the Scala vestibule and the Scala tympani) and the Organ of Corti. Cochlear duct length is defined as the length of the scala media as measured from the middle of the round window to the helicotrema. Preoperative measurement of CDL is significantly important if the desired intracochlear electrode array placement is required. Methods: This retrospective study was done in Mehrotra ENT Hospital, Kanpur, India, which is a tertiary care hospital and referral centre for cochlear implants. We included 800 patients (400 males and 400 females) in the study with bilateral hearing loss who were evaluated for cochlear implantation. HRCT temporal bone of these patients were analyzed and a variable A was measured. Results: Our study included 800 patients, Mean of distance A value for male children is 7.94mm (range 7.0-9.2mm). Mean of distance A value for female children is 7.72mm (range 6.95-8.8mm). So the overall average is 7.83mm. We calculated cochlear duct length using the formula, CDL=4.16A-3.98. The mean cochlear duct length was 28.6mm with a range from 24.9-34.3mm. Conclusions: Our study is one of the most detailed large (800 cases) study of cochlear duct length in the North Indian population. Our results suggest that an average smaller cochlear duct length in our geographical area is a significant finding in the understanding of cochlear anatomy and physiology. It will have great importance on the insertion depth in cochlear implantation.