CT imaging-based approaches to cochlear duct length estimation—a human temporal bone study

Abstract

Objectives Knowledge about cochlear duct length (CDL) may assist electrode choice in cochlear implantation (CI). However, no gold standard for clinical applicable estimation of CDL exists. The aim of this study is (1) to determine the most reliable radiological imaging method and imaging processing software for measuring CDL from clinical routine imaging and (2) to accurately predict the insertion depth of the CI electrode. Methods Twenty human temporal bones were examined using different sectional imaging techniques (high-resolution computed tomography [HRCT] and cone beam computed tomography [CBCT]). CDL was measured using three methods: length estimation using (1) a dedicated preclinical 3D reconstruction software, (2) the established A-value method, and (3) a clinically approved otosurgical planning software. Temporal bones were implanted with a 31.5-mm CI electrode and measurements were compared to a reference based on the CI electrode insertion angle measured by radiographs in Stenvers projection (CDLreference). Results A mean cochlear coverage of 74% (SD 7.4%) was found. The CDLreference showed significant differences to each other method (p < 0.001). The strongest correlation to the CDLreference was found for the otosurgical planning software-based method obtained from HRCT (CDLSW-HRCT; r = 0.87, p < 0.001) and from CBCT (CDLSW-CBCT; r = 0.76, p < 0.001). Overall, CDL was underestimated by each applied method. The inter-rater reliability was fair for the CDL estimation based on 3D reconstruction from CBCT (CDL3D-CBCT; intra-class correlation coefficient [ICC] = 0.43), good for CDL estimation based on 3D reconstruction from HRCT (CDL3D-HRCT; ICC = 0.71), poor for CDL estimation based on the A-value method from HRCT (CDLA-HRCT; ICC = 0.29), and excellent for CDL estimation based on the A-value method from CBCT (CDLA-CBCT; ICC = 0.87) as well as for the CDLSW-HRCT (ICC = 0.94), CDLSW-CBCT (ICC = 0.94) and CDLreference (ICC = 0.87). Conclusions All approaches would have led to an electrode choice of rather too short electrodes. Concerning treatment decisions based on CDL measurements, the otosurgical planning software-based method has to be recommended. The best inter-rater reliability was found for CDLA-CBCT, for CDLSW-HRCT, for CDLSW-CBCT, and for CDLreference. Key Points • Clinically applicable calculations using high-resolution CT and cone beam CT underestimate the cochlear size. • Ten percent of cochlear duct length need to be added to current calculations in order to predict the postoperative CI electrode position. • The clinically approved otosurgical planning software-based method software is the most suitable to estimate the cochlear duct length and shows an excellent inter-rater reliability.

Cochlear and Vestibular Volumes in Inner Ear Malformations

“…The A value (diameter) and B value (width) of the cochlear basal turn were assessed from CT data sets in the oblique coronal view. The H value corresponds to the height of the cochlea, that is, the distance between the apex and the base of the cochlea (20).…”

“…In mild or ambiguous cases of IEM, radiographic measurements may be a crucial diagnostic feature that distinguishes, not only a normal inner ear from an ear exhibiting an IEM, but may also help in differentiating distinct types of IEM from each other. However, currently existing parameters for measuring temporal bone structures are determined in a certain plane of sectional imaging that is chosen individually by each examiner, which significantly contributes to interobserver variability (16,20,21).…”

Vermessung der Cochlea mittels eines Tablet-basierten Softwarepakets: Einfluss der Bildgebungsmodalität und des Untersucherhintergrunds

“…sowie die Nutzung einer otochirurgischen Planungssoftware, und kamen zu dem Ergebnis, dass die Vermessung anhand der Planungssoftware, basierend auf der sog. Elliptic-Circular -Approximation(ECA)-Gleichung, die beste Interraterreliabilität und höchste Korrelation mit den Referenzwerten ergab [ 6 , 11 , 34 ]. Auch Rak et al.…”

“…Bei Breitsprecher et al. ergibt sich in der Ausmessung in der hochauflösenden CT mit der verwendeten Planungssoftware eine mittlere CDL OC von 37,0 ± 1,8 mm, hier wird die CDL OC durch Multiplikation der CDL LW mit 0,9 bestimmt [ 6 ]. Spiegel et al.…”

Systematic Literature Review of Hearing Preservation Rates in Cochlear Implantation Associated With Medium- and Longer-Length Flexible Lateral Wall Electrode Arrays

“…These studies should distinguish between atraumatic and traumatic insertion approaches (RW vs. extended RW/cochleostomy) and factors in cochlear duct length measurements. Current studies report that new otosurgical planning software (Otoplan) is suitable for cochlear size calculations ( 59 ) and cochlear segmentation algorithms will further improve the cochleometric data. As reported in earlier studies ( Figure 1 ), the use of a 28-mm-long electrode can be advocated in the majority of cases.…”