Variability of the mental representation of the cochlear anatomy during cochlear implantation

The aim of this study was to assess the mental representation of the insertion axis of surgeons with different degrees of experience, and reproducibility of the insertion axis in repeated measures. A mastoidectomy and a posterior tympanotomy were prepared in five different artificial temporal bones. A cone-beam CT was performed for each temporal bone and the data were registered on a magnetic navigation system. In these five temporal bones, 16 surgeons (3 experts; >50 cochlear implant surgery/year; 7 fellows with few cochlear implant experience, and 6 residents) were asked to determine the optimal insertion axis according to their mental representation. Compared to a planned ideal axis, the insertion axis was better determined by the experts with higher accuracy (axial: 7° ± 1.5°, coronal: 6° ± 1.5°) than fellows (axial: 14° ± 1.7°, coronal: 13° ± 1.7°; p < 0.05), or residents (axial: 15° ± 1.5°; p < 0.001, coronal: 17° ± 1.9°; p < 0.001). This study suggests that mental representation of the cochlea is experience-dependent. A high variation of the insertion axis to the scala tympani can be observed due to the complexity of the temporal bone anatomy and lack of landmarks to determine scala tympani orientation. Navigation systems can be used to evaluate and improve mental representation of the insertion axis to the scala tympani for cochlear implant surgery.