Dyna-CT of the temporal bone for case-specific three-dimensional rendering of the stapedial muscle for planning of electrically evoked stapedius reflex threshold determination during cochlear implantation directly from the stapedius muscle via a retrofacial approach: a pilot study

Purpose Evaluation of 3D Dyna-CTs to improve cochlear implantation (CI) planning and intraoperative electricallyelicited stapedius reflex threshold (ESRT) measurements. Methods A prospective observational cohort study was performed. Anonymized data collection of Dyna-CTs and CI surgeries in which a retrofacial approach was implemented to access the stapedius muscle. 3D Dyna-CTs of 30 patients and the intraoperative confirmation of the predication in 5/30 patients during CI surgery were evaluated. Inter-rater reliability was also analyzed along with the predictive value of this evaluation. Results 36 representative structures of the middle and inner ear and 3D renderings of the Dyna-CTs were evaluated by four otoneurological surgeons. Fleiss' kappa values for the evaluation of the visibility were high (> 0.7) for most of the anatomical structures. The stapedius muscle was visible in 90% of the cases. Using the 3D data, the retrofacial access to the stapedius muscles was estimated as feasible in 86.7%. Fleiss' kappa value of the evaluation of the accessibility was 0.942. The intraoperative exploration of the stapedius muscle confirmed the preoperative prediction in all five selected patients (four patients with predicted accessibility and one patient with predicted inaccessibility). Conclusions The use of Dyna-CT and 3D rendering is a helpful tool for preoperative planning of cochlear implantations and ESRT measurements from the stapedius muscle via the retrofacial approach.