Morphometric Analysis and Linear Measurements of the Scala Tympani and Implications in Cochlear Implant Electrodes

Abstract

Hypothesis:The objective of this study was to perform detailed height and cross-sectional area measurements of the scala tympani in histologic sections of nondiseased human temporal bones and correlate them with cochlear implant electrode dimensions. Background: Previous investigations in scala tympani dimensions have used microcomputed tomography or casting modalities, which cannot be correlated directly with microanatomy visible on histologic specimens. Methods: Three-dimensional reconstructions of 10 archival human temporal bone specimens with no history of middle or inner ear disease were generated using hematoxylin and eosin histopathologic slides. At 90-degree intervals, the heights of the scala tympani at lateral wall, midscala, and perimodiolar locations were measured, along with cross-sectional area. Results: The vertical height of the scala tympani at its lateral wall significantly decreased from 1.28 to 0.88 mm from 0 to 180 degrees, and the perimodiolar height decreased from 1.20 to 0.85 mm. The cross-sectional area decreased from 2.29 (standard deviation, 0.60) mm 2 to 1.38 (standard deviation, 0.13) mm 2 from 0 to 180 degrees ( p = 0.001). After 360 degrees, the scala tympani shape transitioned from an ovoid to triangular shape, corresponding with a significantly decreased lateral height relative to perimodiolar height. Wide variability was observed among the cochlear implant electrode sizes relative to scala tympani measurements. Conclusion:The present study is the first to conduct detailed measurements of heights and cross-sectional area of the scala tympani and the first to statistically characterize the change in its shape after the basal turn. These measurements have important implications in understanding locations of intracochlear trauma during insertion and electrode design.

Intracochlear Trauma and Local Ossification Patterns Differ Between Straight and Precurved Cochlear Implant Electrodes

“…In the present study, SL perforation was present in 82% of cases with a starting point at an angular insertion depth of 90 to 161 degrees. This angular location is in line with previous studies (29–31) and can be attributed to the changes in ST dimensions along the cochlear duct (32,33).…”

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

“…However, from the current study, the D ST at 180° was 0.88 mm on average, and 0.70 mm in the smallest sample. At deeper insertion depths, the same group found a lateral ST height of 0.53 mm at 630° 26 . Although linear height measurements are of limited value when correlating to 3D electrodes, this measurement would be sufficient to accommodate the longest available electrodes.…”

“…However, all CI electrodes were first generation and these findings may not be relevant to current generation designs. Fujiwara et al 26 . examined the ST in 10 cadaveric temporal bones, although it was not clear if the sample size was sufficient to represent the morphologic variability within the human population 27,28 .…”