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.

Morphologic Analysis of the Scala Tympani Using Synchrotron: Implications for Cochlear Implantation

“…The largest available electrodes (0.52 mm diameter), 59 assuming a circular apical tip, would only occupy 27% of the area in the average ST cross section and 43% in the smallest cochlea. The findings from this current study align with previous findings by Biedron et al ., 56 where histological sectioning was used but limited to 45° incremental measurements; findings by Avci et al ., 16 where μCT was used but measurements could not be conducted past 720°; and with Hussain et al ., 60 who found a ST diameter of 0.64 mm at 720° despite the technical limitations of the underlying model beyond the basal turn 24 …”

“…The largest available electrodes (0.52 mm diameter), 59 assuming a circular apical tip, would only occupy 27% of the area in the average ST cross section and 43% in the smallest cochlea. The findings from this current study align with previous findings by Biedron et al, 56 where histological sectioning was used but limited to 45 incremental measurements; findings by Avci et al, 16 where μCT was used but measurements could not be conducted past 720 ; and with Hussain et al, 60 who found a ST diameter of 0.64 mm at 720 despite the technical limitations of the underlying model beyond the basal turn. 24 The typical electrode tip diameters for the major CI electrode manufacturers include Advanced Bionics HiFocus™ Mid-Scala arrays with an apical diameter of 0.52 mm 59 , Cochlear™ Nucleus ® CI422 Slim Straight arrays with an apical diameter of 0.3 mm 29 , MED-EL FLEXSOFT arrays with an apical minor axis of 0.4 mm 30 , and Oticon Medical EVO ® arrays with a 0.4 mm 31 apical diameter.…”

“…Several studies have reported electrode translocation from the ST to the SV at 180° 24,59–61 . Possible explanations in the literature include: (1) the vertical trajectory of the ST in some cochleae may be prone to translocation, as proposed by Avci et al 16 …”

“…15,41,43 Several studies have reported electrode translocation from the ST to the SV at 180 . 24,[59][60][61] Possible explanations in the literature include: (1) the vertical trajectory of the ST in some cochleae may be prone to translocation, as proposed by Avci et al 16 ; (2) the decrease in area of the ST over the course of the cochlea; and (3) the friction forces may increase at 180 until the end of insertion, as proposed by Torres et al 62 The current analysis suggests another potential explanation for an increased risk of translocation at 180 may be the tilt of the ST, and the associated tilt of the BM. The ST tilt undergoes a maximum decrease over the first 180 , from an average of 50.2 at the RW, to an average of 4.7 at 180 .…”

Optimization of pharmacological interventions in the guinea pig animal model—a new approach to calculate the perilymph volume of the scala tympani

“…For comparison with human studies, the relative standard deviation (RSD) was calculated. Our data showed a volume variability of 14.7% RSD with a total mean volume of 5.3 ± 0.78 μL, comparable studies in humans showed a volume variability between 6.3% RSD (Hussain et al, 2023) to 20% RSD (Dhanasingh et al, 2021). To determine the cochlear "footprint, " the parameters A and B were assessed.…”