Investigating Additional Cochlear Parameters: A follow-up systematic review and meta-analysis.

Objectives: The movement towards personalization of cochlear implantation has continued to generate interest about variabilities in cochlear size. In a recent meta-analysis, Atalay et al. (2022) examined organ of corti length, cochlear lateral wall, and "A" value and found that most covariates, other than congenital sensorineural hearing loss, did not impact cochlear size via these measurements. However, no meta-analysis exists on how patient-specific variables could impact other cochlear size measurements, such as cochlear height (CH), and "B" value (defined as the distance between opposite lateral walls and perpendicular to "A" value). The purpose of this systematic review and meta-analysis is to examine how patient-specific variables impact additional cochlear size measurements to assist clinical decision-making. Databases reviewed: A systematic review for cochlear size measurements using PRISMA methodology was performed using PubMed, CINAHL, and MEDLINE from database inception to October 1st, 2022. Methods: Search terms used included English, cochlea, size, histology, anatomy, and human. Inclusion criteria were measurements for human cochlea, full-text articles, and articles in English. Primary measurements were "B" value and CH, as these measurements differ from the recent meta-analysis on this topic. Cochlear duct length (CDL) was also included. A random-effects continuous model for meta-analysis was performed. Measurements were stratified by gender (male/female) and disease type (sensorineural hearing loss (SNHL)/conductive hearing loss (CHL)). Results: A total of 7 articles met final inclusion criteria from a total of 674 articles received on initial search, resulting in 2263 total human cochleae. There was a statistical difference between male CDL (n = 681 cochlea) compared to female CDL (n = 657) from four articles (p < 0.001; Cohen's d effect size (ES):0.421; 95% confidence intervals (CI): 0.171, 0.671). The frequency weighted mean for male CDL was 33.5 mm ± 1.8 mm and the frequency weighted mean for female CDL was 32.4 mm ± 1.5 mm with an unstandardized mean difference of 0.854 mm. There was no statistical difference between male "B" value (n = 329) and female "B" value (n = 349) for cochlea from two studies (p = 0.184; Cohen's d ES: 0.410; 95% CI: 0.194, 1.014). The frequency weighted mean for male "B" value was 6.5 mm ± 0.1 mm and the frequency weighted mean for female "B" value was 6.4 mm ± 0.1 mm with an unstandardized mean difference of 0.126 mm. There was no statistical difference between CH for SNHL (n = 282) and CHL (n = 275) from two studies (p = 0.486; ES: 0.085; 95% CI: 0.323, 0.153, F ig. 3). The frequency weighted mean for SNHL CH was 4.6 mm ± 0.8 mm and the frequency weighted mean for CHL CH was 4.3 mm ± 0.8 mm with an unstandardized mean difference of 0.032 mm. Conclusion: Male CDL is statistically larger than female CDL. There is no statistically significant association between gender or hearing loss type and "B" value or CH. The effect size for all comparisons is small, indicating little practical significance between any existing differences. The results of this study provide two additional cochlear metrics and indicate similar findings to the study by Atalay and colleagues as patient-specific characteristics appear to have no statistically significantly impact on cochlear size.