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.

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Objective: The aim of this study was to evaluate the audiological performance of the ADHEAR system and to compare it with a softband BAHA system in adults with middle ear disease. Study Design: Prospective, single-subject, repeated-measures study Setting: Monocentric study Participants: In 23 patients with mild to moderate isolated conductive or combined hearing loss (CHL) the ADHEAR system was tested, where 12 of them were outside of the ADHEAR indication. In ten patients, testing was performed with the ADHEAR system and a softband BAHA system. A control group consisted of 10 patients with bilateral artificial occluded ear canal. Main outcome measures: Air and bone conduction thresholds and free-field monosyllable speech intelligibility thresholds in quiet and in noise were measured and evaluated in an unaided situation and aided situation. Furthermore, an ADHEAR questionnaire was assessed. Results: In patients with a middle ear disease compared to the unaided situation, the aided situations with the ADHEAR system and the softband BAHA system led to a significant improvement of speech intelligibility in quiet and in noise. In terms of the ADHEAR questionnaire, using the ADHEAR system patients reported about an improvement in sound localization, sound quality and speech intelligibility. Conclusions: The results show that patients with middle ear disease can benefit from the ADHEAR system, even if their hearing loss is outside of its indication. Outside the indication criteria of the ADHEAR system, it can be an option.