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Hypothesis: Image quality of low-dose multi-slice computed tomography (MSCT) after cochlear implantation is comparable to that of cone-beam computed tomography (CBCT)., Background: CBCT has been described as a low-dose alternative with superior image quality to MSCT for postoperative cochlear implant (CI) imaging, but to our knowledge, no dose-matched comparisons of image quality have been published., Materials and Methods: Five human cochleae were implanted with CI electrodes and scanned on two CBCT and two MSCT systems. Four independent observers rated aspects of image quality on a five-point scale. CBCT scans were compared to clinical and dose-matched MSCT scans. Declining-dose MSCT protocols were compared to the clinical protocol. CT phantoms were used to determine effective dose and resolution for each acquisition protocol., Results: Effective dose of the CBCT protocols was 6 to 16% of the clinical MSCT dose. Visibility of cochlear inner and outer walls and overall image quality were positively correlated with radiation dose on MSCT and image quality was better with clinical MSCT than with CBCT protocols. In other comparisons, differences between systems were found, but a distinction between CBCT and MSCT could not be made., Conclusion: CBCT and dose-matched MSCT are both suitable for postoperative CI imaging. Selecting a CT system and radiation dose depends on which cochlear structures need to be visualized.

Objective: To develop a transmastoid-posterior tympanotomy approach for the implantation of a penetrating auditory prosthesis in the most distal portion of the cochlear nerve., Background: Animal studies suggest that penetrating cochlear nerve implants may overcome limitations of current cochlear implant systems. One step toward human implantation is the development of a suitable surgical approach., Methods: In computer-rendered 3-dimensional (3-D) models (based on micro-CT scans of 10 human temporal bones), we simulated trajectories through the most basal part of the cochlea that gave access to the most distal portion of the cochlear nerve with minimal damage to intracochlear structures. We determined their vectors with respect to the mid-modiolar axis and posterior round window edge and assessed if they intersected the chorda tympani nerve., Results: The typical vector obtained with these 3-D models ran in an anterosuperior direction, through the inferior part of the facial recess and anterior round window edge. In 7 of 10 temporal bones, this trajectory intersected the chorda tympani nerve. Based on the vectors, dummy probes were implanted in 3 of 10 temporal bones, and the need for chorda tympani removal was confirmed in accordance with the 3-D models. Postoperative micro-CT scans revealed that all probes were successfully implanted in the cochlear nerve, whereas the osseous spiral lamina and basilar membrane were preserved., Conclusion: The vector for drilling and implantation found in this study can be used as a guideline for real-life surgery and, therefore, is another step toward the clinical implementation of cochlear nerve implants.