Radiological and Histological Evaluation of Perimodular Electrodes: Impact on Cochlear Implant Development

Introduction: Different Perimodiolar electrodes were developed by many cochlear implant (CI) manufacturers in the past few years. Possible advantages are lower stimulation thresholds and a better channel separation. A position close to the modiolus can be facilitated by different means: preformed electrode shape (Nucleus ContourTM electrode, Cochlear Corp., Australia), additional positioning elements like silicon in a space-filling matter (Clarion 1.2® electrode with positioner and HiFocus® electrode with positioner, Advanced Bionics Corp., USA) and additional silicon-covered wires that allow a positioning of the electrode lead by retropositioning after insertion (perimodiolar electrode, MedEl Company, Austria). The Aim of this Work is to: Assess the position of different perimodular electrodes inside the cochlea and their impact on the fine intra-cochlear structure (insertion trauma). Methodology: Different perimodular electrodes (Contour, Med-El, Clarion 1.2 and Clarion HiFocus II with positioner) were implanted in fresh frozen temporal bones. Assessment was carried out radiologically by digital subtraction analysis (rotational tomography) for position of electrode with regard to the modiolus, tympanic and vestibular scale. Histological preparation was focused on possible intracochlear trauma. Results and Conclusion: All different types of electrodes may generate a design-specific kind of intracochlear damage that might be classified into minor or major damage. Major trauma may be responsible for the development of postoperative meningitis that has been recorded lately. Further developments of electrodes have to consider the specific intracochlear geometry to allow ideal positioning of electrodes with minimal intracochlear trauma.