Migration of the ball electrode after cochlear implantation.

OBJECTIVE: To review the postoperative radiographic investigations of patients implanted with a cochlear implant. STUDY DESIGN: Retrospective case series. PATIENTS: Thirty-nine patients (22-77 yrs old) implanted for sensorineural deafness in the cochlear implants program of the Academic Medical Center of Amsterdam. INTERVENTION: Cochlear implantation with Cochlear Nucleus 24 Contour and Cochlear Nucleus Freedom (Cochlear Corp., Lane Cove, New South Wales, Australia) implant. RESULTS: This retrospective analysis of the postoperative computed tomographic scans showed that, in a large number of the implantations, the external ball electrode of the cochlear implant migrated from the insertion place toward the magnet of the receiver/stimulator unit of the implant. It seems that this migration of the external ball electrode does not influence the function of the cochlear implant and the result of the hearing rehabilitation in the short term. CONCLUSION: Because of the magnetic field of the receiver/stimulator unit of the cochlear implant and the magnet of the external transmitting coil of the speech processor, it seems to be possible that the extracochlear ball electrode can migrate in the space between the temporal bone and the temporal muscle during the postoperative healing phase. The importance of our observation is still not clear.