Investigations on the clinical significance of cochlear implantation in the modiolus

Abstract

Problem: The purpose of this study was to disclose the possibilities for implantation of an electrode in the modiolus for stimulation of auditory nerve in cases of severe hearing loss. Methods: Our methods consisted of the dissection of human temporal bones, and histological investigation of modiolar structure before and after the insertion of an electrode. Results: Ten dissections of human temporal bones were carried out. A plastic copy of an electrode was implanted in the modiolus. Histological investigations were made in order to clarify the anatomic variations of modiolus and the eventual destructive changes that may occur during the implantation. Conclusion: It was found that the best surgical approach to the modiolus is through middle cranial fossa. The cupula of the cochlea is located medially and anteriorly to ganglion geniculi. The greater petrosal nerve serves as a landmark. The nerve is elevated, the bone is drilled from its sulcus to the cupula cochleae, which is found at about 2 mm depth. After entering the cupula, the top of the modiolus is visualized. A canal should be made by a special probe, which should be introduced without any pressure along canalis longitudinalis modioli, due to the very soft modiolar tissue. Invasion of the electrode into the first 2 mm of internal auditory canal does not harm the hearing nerve fibers, which are still not fused to form the auditory nerve. Histological studies did not show injury of modiolar structures. Significance: We believe that the implantation of an electrode in the modiolus could be an alternative to standard cochlear implantation and may even be preferable in cases with chronic middle ear inflammation and cochlear ossification. Support: None reported.