Anatomical Variations of the Human Cochlea Using an Image Analysis Tool

Abstract

Understanding cochlear anatomy is crucial for developing less traumatic electrode arrays and insertion guidance for cochlear implantation. The human cochlea shows considerable variability in size and morphology. This study analyses 1000+ clinical temporal bone CT images using a web-based image analysis tool. Cochlear size and shape parameters were obtained to determine population statistics and perform regression and correlation analysis. The analysis revealed that cochlear morphology follows Gaussian distribution, while cochlear dimensions A and B are not well-correlated to each other. Additionally, dimension B is more correlated to duct lengths, the wrapping factor and volume than dimension A. The scala tympani size varies considerably among the population, with the size generally decreasing along insertion depth with dimensional jumps through the trajectory. The mean scala tympani radius was 0.32 mm near the 720° insertion angle. Inter-individual variability was four times that of intra-individual variation. On average, the dimensions of both ears are similar. However, statistically significant differences in clinical dimensions were observed between ears of the same patient, suggesting that size and shape are not the same. Harnessing deep learning-based, automated image analysis tools, our results yielded important insights into cochlear morphology and implant development, helping to reduce insertion trauma and preserving residual hearing.

Keywords: cochlear implantation; cochlear morphology; statistical analysis.

Figure 1

Description of clinical metrics computed by Nautilus. A: maximum length between round window and lateral wall; B: maximum perpendicular length to A. h: height of cochlea; h: maximum vertical ST height; r: radius of maximum circle that can fit in ST; ST: scala tympani; SV: scala vestibuli; BM: basilar membrane; OC: organ of corti; LW: lateral wall; MW: modiolar wall.

Figure 2

Population statistics and correlation plots between anatomical features of the cochlea. Histograms of the parameters with fitted Gaussian curves are shown in the diagonal of the matrix. Scatter plots show the correlation between the parameter indicated in the column titles and the parameter in the row titles. A strong correlation (ρ > |0.50|) between parameters is represented by scatter plots with filled circles and a weak correlation is shown by empty circles. Solid lines indicate the linear regression curves. Note that the scales of the y-axes do not apply to the histograms. ρ: Pearson correlation coefficient; µ: mean; σ: standard deviation; * depicts a significant correlation (p-value < 0.05).

Figure 3

Correlation plots between cochlear duct lengths and cochlear size. A strong correlation (ρ > |0.50|) between parameters is represented by scatter plots with filled circles and a weak correlation is shown by empty circles. Solid lines indicate the linear regression curves. ρ: Pearson correlation coefficient, * depicts significant correlation (p-value < 0.05).

Figure 4

Scala tympani maximum vertical height (A), area (B) and radius of largest fitted circle (C) as a function of the angular distance. Dots represent individual measurement points. Error bars represent the mean and ±1 standard deviation; dotted lines show the 10th and 90th percentiles. Vertical dotted grid lines indicate the angular distance bands that were used to select the N measurement points indicated at the top of panel A to calculate the statistics.

Figure 5

Inter-sex population comparison depicting that female ears are generally smaller and more tightly wound than male ears. CDL (LW): lateral wall cochlear duct length.

Figure 6

Intra-patient population and comparative correlation plots for imaging and clinical parameters. Strong correlations (ρ > |0.50|) between parameters are represented by scatter plots with filled circles and weak correlations are shown by empty circles. Ρ: Pearson correlation coefficient; µ: mean; σ: standard deviation; * depicts significant relation (p-value < 0.05).