Abstract
Although the spiral anatomy of the human cochlea seems evident, measuring the highly inter-variable true dimensions is still challenging. Today, only a few three-dimensional reconstruction models of the inner ear are available. Previously, spiral equations were applied to two-dimensional computed tomography (CT) images to predict the electrode insertion depth prior to cochlear implantation. The study aimed primarily to compare the clinical applicability of two analytical cochlear models using a recently introduced planning software to predict the insertion depth of the electrode array of 46 cochlear implant recipients. One was based upon the Escudé formula, which relies only on the basal turn diameter, and another based upon the Elliptic-Circular Approximation (ECA), using the diameter and width. Each case was measured twice by two ENT surgeons. Secondly, in order to measure the benefit of the new planning software over the use of the existing clinical routine method, the results were compared to the prediction based upon a two-dimensional CT image. The intra -and inter-observer agreement using the planning software was significantly better when the ECA was applied, compared to the Escudé formula (p < 0.01). As a reference, the predicted insertion depth was compared to the actual insertion depth measured on post-operative images. The mean absolute error was |2.36| (|1.11|) mm in case of the Escudé approach and |1.19| (|0.92|) mm in case of the ECA. The use of a new planning software that allows three-dimensional handling, integrating the diameter and width of the basal turn (ECA formula), resulted in the most accurate predictions of the electrode insertion depths.
Highlights
Www.nature.com/scientificreports insertion angles produce greater degrees of cochlear coverage in the apical regions and better tonotopic place representation for stimulation[9]
To be able to investigate these analytical cochlear models, there is a need for a planning software that allows three-dimensional handling to provide a quick individualized oblique view of the cochlea based on clinically available computed tomography (CT) images
The standard deviation of the differences between the two observations reduced significantly (Wilcoxon Signed Rank test, p < 0.01) when Elliptic-Circular Approximation (ECA) was used (SDOBSERVER_1 42.06°, SDOBSERVER_2 47.41°) for the prediction of the electrode insertion depth at C1 compared to the Escudé approach (SDOBSERVER_1 65.06°, SDOBSERVER_2 68.69°)
Summary
Www.nature.com/scientificreports insertion angles produce greater degrees of cochlear coverage in the apical regions and better tonotopic place representation for stimulation[9]. Consistent protocols were developed to graphically represent the CDL by using landmarks from histological sections or plastic casts[12,13,14] This indirect method has some major drawbacks. Three-dimensional reconstructions on the other hand, consider the entire three-dimensional shape of the cochlea Since they are not susceptible to the viewing angle effects, they are the most accurate models to measure the CDL10,16–18. Escudé et al defined a logarithmic equation to determine the CDL at the level of the lateral wall at each cochlear angle θ using a single linear measurement of basal turn diameter A21. The primary aim of the retrospective single-centre study was to investigate the clinical applicability of two analytical cochlear models using a recently introduced planning software that allows three-dimensional handling to predict the electrode insertion depth prior to cochlear implantation. The predicted electrode insertion depths were validated by comparing them to the post-operative actual insertion depth
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