Variations in microanatomy of the human cochlea

Abstract

The human cochlea shows considerable interindividual variability in size and morphology. In order to develop atraumatic cochlear implant (CI) electrodes, high-precision details of the variability of human anatomy are required. Sixteen human temporal bones were cut around the cochlea in blocks of approximately 3.5 × 3.5 cm. The bones were scanned by using a Skyscan 1173 micro-computed tomography (μCT) device. Mimics software (Materialise, Leuven, Belgium) was used to segment out the scala tympani (ST) from the μCT images. A three-dimensional surface model of the segmented area was generated for each cochlea. Cross-sectional images were taken and analyzed by custom-designed software in MATLAB. Comparison of different STs showed large variability in cross-sectional diameter (CSD), vertical trajectory, and height of the ST. Relative standard deviations of the CSD were between 9 and 15%. Heights measured at the center of the ST exceeded those in the modiolar and lateral regions of the scala. At the lateral region, the height decreased significantly at the beginning of the second turn. In the vertical trajectory, critical anatomic features were observed, such as dips, vertical jumps, and peaks. Rosenthal's canal (RC) extended to between 560 and 650°. We found a correlation between the length of the RC and that of the ST. The ST was segmented and the internal dimensions measured by using μCT. We observed large dimensional variability between different STs. These differences could have considerable implications for approaches to the design of CI arrays, especially in terms of their ability to preserve residual hearing during insertion of the electrode array. J. Comp. Neurol. 522:3245–3261, 2014. © 2014 Wiley Periodicals, Inc.

Automated analysis of human cochlea shape variability from segmented μ CT images

“…In order to evaluate the internal dimensions of the cochlea, cross-section measurements were performed in radial planes (a.k.a mid-modiolar cross-sections) (Zrunek et al, 1980;Zrunek and Lischka, 1981;Erixon et al, 2009), in parallel planes such as histological sections (Biedron et al, 2010) and in planes normal to the centerline (Poznyakovskiy et al, 2011;Avci et al, 2014). This last method does not induce measurement errors (e.g.…”

“…Avci et al (2014) defined categories of the longitudinal component of the tympanic centerline. Among other categories, the "rollercoaster" category was defined as a decreasing longitudinal component from the round window, changing to an increasing curve between 5 and 10 mm.…”

“…As important cochlear anatomical structures such as the basilar membrane are not visible in CT imaging, analyses of the cochlea are commonly performed using µCT images (Verbist et al, 2009;Poznyakovskiy et al, 2011;Gunz et al, 2012;Shin et al, 2013;Avci et al, 2014;Ceresa et al, 2014). In order to improve contrast, temporal bone samples can be fixed and stained before imaging (Poznyakovskiy et al, 2011).…”

“…In order to improve contrast, temporal bone samples can be fixed and stained before imaging (Poznyakovskiy et al, 2011). Cochlear fluids are commonly removed (Postnov et al, 2006;Poznyakovskiy et al, 2011;Avci et al, 2014;Ceresa et al, 2014) but this operation requires to drill through the round and oval windows and to replace the perilymph with air by suction. The influence of this method on the geometry of the membranous structures is unknown (Rau et al, 2013) and µCT scanning with fluid removal cannot be considered as nondestructive.…”

“…Previous analyses include measurements of the length of the cochlea and the number of cochlear turns (Hardy, 1938;Kawano et al, 1996;Skinner et al, 2002;Escudé et al, 2006;Stakhovskaya et al, 2007;Erixon et al, 2009;Gunz et al, 2012;Shin et al, 2013;van der Marel et al, 2014), measurements of the heights, widths and sectional areas of the scala tympani (Zrunek et al, 1980;Zrunek and Lischka, 1981;Hatsushika et al, 1990;Gulya and Steenerson, 1996;Wysocki, 1999;Thorne et al, 1999;Biedron et al, 2010;Avci et al, 2014), the scala vestibuli (Zrunek and Lischka, 1981;Gulya and Steenerson, 1996;Wysocki, 1999;Thorne et al, 1999;Biedron et al, 2010) and the cochlea (Erixon et al, 2009;Shin et al, 2013), measurements of the radial component of the cochlear centerlines (also called cochlear curvature) (Cohen et al, 1996;Baker, 2008;van der Marel et al, 2014), and studies of the longitudinal component of the centerlines of the scala tympani (Avci et al, 2014) and the cochlea itself (Verbist et al, 2009).…”