Optimal Cochlear Implant Insertion Vectors

Hypothesis: An optimal insertion trajectory during cochlear implantation may be determined from the anatomic relationship between the facial nerve and round window. Background: Cochlear implantation functional outcomes improve with insertion of the implant into the scala tympani. This depends on creating a cochleostomy in the proper position and inserting the electrode along a trajectory coaxial with the centerline of the scala tympani. The anatomic landmarks for this insertion trajectory have not been described. Methods: Clinical computed tomography and micro-computed tomographic analysis of 8 cadaveric temporal bones. Results: Appropriate insertion vectors pass inferior or anteroinferior to the round window membrane. In many individuals, the facial nerve interrupts all or most of the insertion vectors coaxial to the centerline of the scala tympani. Conclusion: A cochleostomy placed inferior or anteroinferior to the round window membrane may facilitate atraumatic insertion of a cochlear implant along the centerline of the scala tympani. The lateral and anterior wall of the fallopian canal must be adequately thinned to achieve an optimal insertion trajectory. This is particularly true when inserting through cochleostomies placed away from the round window along the basal turn of the cochlea.