RE: REIMPLANTATION OF HYBRID COCHLEAR IMPLANT USERS WITH A FULL-LENGTH ELECTRODE AFTER LOSS OF RESIDUAL HEARING

Abstract

To the Editor: We read with great interest the recent article by Fitzgerald et al. (1) entitled "Reimplantation of Hybrid Cochlear Implant Users With a Full-Length Electrode After Loss of Residual Hearing." In this report, 2 patients with residual hearing were first implanted with a Nucleus 10-mm hybrid electrode array and then reimplanted with a full-length Nucleus Freedom array after loss of residual hearing. As expected, speech understanding and pitch scaling improved considerably after reimplantation. These improvements were attributed to the deeper insertion depth rather than to the additional experience of the patients. We want to express our appreciation to the authors for their interesting report, and because one of our former studies (2) on this topic was cited in the article, we would like to comment on our actual strategy concerning cochlear implantation for electric acoustic stimulation (EAS). Despite all efforts to preserve hearing after cochlear implantation, a small group of patients who do lose their residual hearing remain and are then completely dependent on their implant. We believe that providing best possible conditions for these patients is one of the major concerns in EAS surgery. Hereby, the crucial point is to find the trade-off between a shallow insertion depth to reduce the risk of damage to apical cochlear structures (3) and a sufficiently deep insertion of the array to guarantee satisfying performance with the cochlear implant alone in case of loss of residual hearing (4). Shallow implantation of a very short array and reimplantation of a full-length array in case of loss of residual hearing is 1 possible approach, as described by Fitzgerald et al. In our experience, a 360-degree insertion of the array (corresponding to 18-24 mm 5,6) so that it enters the 1,000-Hz region, which defines the end of electric stimulation and beginning of acoustic stimulation, sufficiently complies with the requirements mentioned, without the need for reimplantation. Because considerable anatomic variations of cochlear diameters exist, we found significant variations of insertion degrees at constant surgical depths. Therefore, we developed a radiologic method to preoperatively predict the required insertion depth to achieve a 360-degree insertion (5). This protocol is based on a high-resolution computer tomography and a 3-dimensional placement of referral points. The method achieved fairly good accuracies if measurements included the basal and first part of the middle cochlear turn only (6). In an unpublished series of EAS patients using a new atraumatic electrode array, we could achieve, so far, an unattained high rate of hearing preservation. Nevertheless, until now, not all factors leading to hearing loss after electrode insertion are known, and there remains a small subgroup of patients who experience complete deafness after implantation. Therefore, we think that the protocol described is most accurate to provide good cochlear implant performance for both combined EAS and electrical stimulation alone in case of loss of residual hearing. Wolfgang Gstoettner, M.D., Ph.D. Christoph Arnoldner, M.D. Department of Otorhinolaryngology Johann Wolfgang Goethe University Frankfurt am Main, Germany