Evaluation of a Radiological Tool for Semiautomatic Scalar Translocation Detection After Cochlear Implantation.

OBJECTIVE: To evaluate the clinical applicability of a semiautomatic radiological tool for scalar translocation detection. STUDY DESIGN: Retrospective study. SETTING: Tertiary care academic center. PATIENTS: We included 104 patients implanted with 116 HiFocus Mid-Scala electrode arrays between January 2013 and September 2016. INTERVENTION: Cochlear implantation. MAIN OUTCOME MEASURES: The tool's scalar position assessments were compared with manual ones by calculating intraclass coefficient (ICC) for individual contacts and sensitivity and specificity for translocation detection of the whole array. In addition, ICC was calculated for diameters A and B, ratio A/B, and angular insertion depth (AID). RESULTS: Nine-one percent of cases could be processed, which took 5 to 10 minutes per case. Comparison of manual and semiautomatic scalar position showed for individual contacts an ICC of 0.89 and for the whole array a sensitivity of 97% and a specificity of 96%. ICCs for A, B, and A/B were 0.82, 0.74, and 0.39 respectively. For AID, ICC of each of the 16 contacts was 0.95 or higher. CONCLUSIONS: The semiautomatic radiological tool could analyze most cases and showed good to excellent agreement with manual assessments for translocation detection, diameter A, diameter B, and AID. The variability between semiautomatic and manual measurements is comparable to interobserver variability, indicating that clinical implementation of the tool is feasible.

Three-Dimensional Force Profile During Cochlear Implantation Depends on Individual Geometry and Insertion Trauma.

OBJECTIVES: To preserve the acoustic hearing, cochlear implantation has to be as atraumatic as possible. Therefore, understanding the impact of the cochlear geometry on insertion forces and intracochlear trauma might help to adapt and improve the electrode insertion and reduce the probability of intracochlear trauma. DESIGN: The study was conducted on 10 fresh-frozen human temporal bones. The inner ear was removed from the temporal bone. The bony capsule covering the scala vestibuli was removed and the dissected inner ear was mounted on the three-dimensional (3D) force measurement system (Agilent technologies, Nano UTM, Santa Clare, CA). A lateral wall electrode array was inserted, and the forces were recorded in three dimensions with a sensitivity of 2 µN. Afterwards, the bones were scanned using a Skyscan 1173 micro-computed tomography (micro-CT). The obtained 3D force profiles were correlated with the videos of the insertions recorded through the microscope, and the micro-CT images. RESULTS: A correlation was found between intracochlear force profiles measured in three different directions with intracochlear trauma detected with micro-CT imaging. The angle of insertion and the cochlear geometry had a significant impact on the electrode array insertion forces and possible insertion trauma. Intracochlear trauma occurred frequently within the first 180° from the round window, where buckling of the proximal part of the electrode carrier inside the cochlea, and rupturing of the spiral ligament was observed. CONCLUSIONS: The combination of the 3D force measurement system and micro-CT can be used to characterize the mechanical behavior of a CI electrode array and some forms of insertion trauma. Intracochlear trauma does not always correlate with higher force amplitudes, but rather with an abrupt change of force directions.

Variations in microanatomy of the human cochlea.

The human cochlea shows considerable interindividual variability in size and morphology. In order to develop atraumatic cochlear implant (CI) electrodes, high-precision details of the variability of human anatomy are required. Sixteen human temporal bones were cut around the cochlea in blocks of approximately 3.5 × 3.5 cm. The bones were scanned by using a Skyscan 1173 micro-computed tomography (µCT) device. Mimics software (Materialise, Leuven, Belgium) was used to segment out the scala tympani (ST) from the µCT images. A three-dimensional surface model of the segmented area was generated for each cochlea. Cross-sectional images were taken and analyzed by custom-designed software in MATLAB. Comparison of different STs showed large variability in cross-sectional diameter (CSD), vertical trajectory, and height of the ST. Relative standard deviations of the CSD were between 9 and 15%. Heights measured at the center of the ST exceeded those in the modiolar and lateral regions of the scala. At the lateral region, the height decreased significantly at the beginning of the second turn. In the vertical trajectory, critical anatomic features were observed, such as dips, vertical jumps, and peaks. Rosenthal's canal (RC) extended to between 560 and 650°. We found a correlation between the length of the RC and that of the ST. The ST was segmented and the internal dimensions measured by using µCT. We observed large dimensional variability between different STs. These differences could have considerable implications for approaches to the design of CI arrays, especially in terms of their ability to preserve residual hearing during insertion of the electrode array.