Into and out of the cochlea: A re-implantation saga.

Introduction: In patients with normal inner ear architecture at imaging and who received a prior cochlear implant (CI) without difficulty, the expectation is that replacing a failed CI should be straightforward. Here, we present a patient in whom an unusual complication (to our knowledge, not reported) was encountered. Methods: Review of audiological and medical and surgical records and imaging data. Results: Re-implantation went well except no electrically elicited compound action potential could be elicited via any electrode. The replacement CI did not provide any auditory perception. CT showed the electrode array to enter the cochlea with three electrodes, but all other electrodes extended toward the Eustachian tube. Subsequent re-implantation into the scala vestibuli yielded excellent performance with the CI. Conclusion: Mechanical forces, such as from a CI array, can erode the hardest bone over time. This possibility should be a consideration in patients who are undergoing CI device replacement.

Implanting straight into cochlea risks the facial nerve: a Cartesian coordinate study.

PURPOSE: To describe the straight-into-cochlea line that affords the best access for an electrode array to enter via the round window, and how this line relates to the facial nerve, the incus, and mastoid size. The straight-into-cochlea line is important to minimize the cochlear trauma and maximize the likelihood of placement into the scala tympani. METHODS: High-resolution CT scans were obtained for ten craniums with the extremes of large (N = 5) and small (N = 5) mastoid pneumatization; the specimens were from a series of 41 ear normal craniums. Using FIJI, a publicly available software program, the straight-into-cochlea insertion line was determined by defining the x-y-z coordinates of the middle of the round window and a point 6.0 mm into the cochlea on its centrifugal wall. Then, from the extended straight-into-cochlea insertion line, we determined the shortest perpendicular distance to the middle of the fallopian canal, and from that "fallopian point" to the apex of the posterior process of the incus. RESULTS: We found good repeatability of measurements. We found the extended straight-into-cochlea insertion lines routinely close to or in the midst of the fallopian canal (50 % ≤ 1.0 mm). We found the lines 4.7-7.8 mm from the apex of the posterior process of the incus. Line positions relative to "fallopian point" and incus showed no relation to mastoid pneumatization. For the distance "fallopian point" to incus, bilateral symmetry was suggested. CONCLUSIONS: Using landmarks registered in an x-y-z coordinate system, straight-into-cochlea insertion via the round window puts the facial nerve at risk.