The Use of Clinically Measurable Cochlear Parameters in Cochlear Implant Surgery as Indicators for Size, Shape, and Orientation of the Scala Tympani

Abstract

Objectives: (1) To assess variations of the human intracochlear anatomy and quantify factors which might be relevant for cochlear implantation (CI) regarding surgical technique and electrode design. (2) Search for correlations of these factors with clinically assessable measurements. Design: Human temporal bone study with micro computed tomography (μCT) data and analysis of intracochlear geometrical variations: μCT data of 15 fresh human temporal bones was generated, and the intracochlear lumina scala tympani (ST) and scala vestibuli were manually segmented using custom software specifically designed for accurate cochlear segmentation. The corresponding datasets were processed yielding 15 detailed, three-dimensional cochlear models which were investigated in terms of the scalae height, cross-sectional size, and rotation as well as the interrelation of these factors and correlations to others. Results: The greatest anatomical variability was observed within the round window region of the cochlea (basal 45°), especially regarding the cross-sectional size of the ST and its orientation relative to the scala vestibuli, which were found to be correlated (p < 0.001). The cross-sectional height of the ST changes substantially for both increasing cochlear angles and lateral wall distances. Even small cochleae were found to contain enough space for all commercially available CI arrays. Significant correlations of individual intracochlear parameters to clinically assessable ones were found despite the small sample size. Conclusion: While there is generally enough space within the ST for CI, strong intracochlear anatomical variations could be observed highlighting the relevance of both soft surgical technique as well as a highly flexible and self-adapting cochlear implant electrode array design. Cochlear dimensions (especially at the round window) could potentially be used to indicate surgically challenging anatomies.

Uncoiling the Human Cochlea—Physical Scala Tympani Models to Study Pharmacokinetics Inside the Inner Ear

“…The fundamental data used for the investigation was previously presented in two earlier studies from our group [6,15]. It consists of 15 micro CT datasets in which cross sections of scala tympani (ST), scala vestibuli (SV), basilar membrane (BM) and helicotrema (HT) region were manually segmented using a custom software tool specifically designed for this task [32].…”

“…An equally important factor to be considered is the rotation of the cross sections [6]. Figure 1D shows two qualitatively identical cross sections of different size and with a different angular orientation.…”

“…In contrast, thereto, neglecting the different angular orientations yields a shape falsification when averaging. That is why all shapes were rotated to the cochlear angle dependent average orientation of the BM [6] prior to point redistribution and averaging.…”

“…To begin with, the anatomy of the ST is highly variable [3][4][5][6]. Experimental findings derived with a model which is founded on one specific ST shape [7] may hence not hold true in general but be specific to that ST [8,9].…”

“…Experimental findings derived with a model which is founded on one specific ST shape [7] may hence not hold true in general but be specific to that ST [8,9]. It may therefore be advisable to create an average model of a ST [10], but it is not clear how the known variations of the ST shape (e.g., crosssectional profile [11] and size [3,6,12]) should be averaged without losing fundamental anatomical features of the ST [13,14]. On the other hand, certain simplifications of the ST may be tolerable if they are unlikely to influence the parameters of interest of a specific study.…”