Hypothesis:Suboptimal cochlear implant (CI) electrode array placement may reduce presentation of coded information to the central nervous system and, consequently, limit speech recognition.Background:Generally, mean speech reception scores for CI recipients are similar across different CI systems, y

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Role of electrode placement as a contributor to variability in cochlear implant outcomes.

The cochlear implant is the most successful of all neural prostheses developed to date. It is the most effective prosthesis in terms of restoration of function, and the people who have received a cochlear implant outnumber the recipients of other types of neural prostheses by orders of magnitude. The primary purpose of this article is to provide an overview of contemporary cochlear implants from the perspective of two designers of implant systems. That perspective includes the anatomical situation presented by the deaf cochlea and how the different parts of an implant system (including the user's brain) must work together to produce the best results. In particular, we present the design considerations just mentioned and then describe in detail how the current levels of performance have been achieved. We also describe two recent advances in implant design and performance. In concluding sections, we first present strengths and limitations of present systems and then offer some possibilities for further improvements in this technology. In all, remarkable progress has been made in the development of cochlear implants but much room still remains for improvements, especially for patients presently at the low end of the performance spectrum.

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Cochlear implants: current designs and future possibilities.

There are numerous advantages for patients who can add residual acoustic hearing to the electric stimulation of a cochlear implant. When cochlear implantation was first becoming accepted, patients were typically profoundly deaf in both ears, so any possible advantages of also using acoustic hearing were non-existent. However, as time progressed and the range of patients considered for implantation was expanded to include those with more and more residual hearing, this remaining acoustic hearing became a factor to consider. The residual acoustic hearing was at first most often located in the non-implanted ear, especially since the trend has been to place the implant in the poorer ear if there was any aidable hearing. In recent years, residual acoustic hearing has been preserved even in the implanted ear, whereby acoustic and electric hearing are combined in the same ear. It turns out that the acoustic hearing that remains in either ear after cochlear implantation can still contribute to overall performance in some very significant ways, including cases where, by itself, the acoustic hearing produces only minimal or no word recognition.

Combining acoustic and electrical hearing

Aims: To establish normative data on the size of the basal turn of the cochlea using high-resolution computed tomography of the temporal bone in adults and children. To determine wh

The size of the cochlea and predictions of insertion depth angles for cochlear implant electrodes.

Objective:To assess the conservation of residual hearing in recipients of the Nucleus 24 Contour Advance cochlear implant (CI) and the benefits of combined electrical and acoustic stimulation.Study Design:Prospective multicenter study.Setting:CI clinics in Western Europe.Patients:Adult candidates fo

Residual hearing conservation and electroacoustic stimulation with the nucleus 24 contour advance cochlear implant.

CONCLUSIONS: Hearing may be conserved in adults after implantation with the Nucleus Contour Advance perimodiolar electrode array. The degree of hearing preservation and the maximum insertion depth of the electrode array can vary considerably despite a defined surgical protocol. Residual hearing combined with electrical stimulation in the same ear can provide additional benefits even for conventional candidates for cochlear implantation. OBJECTIVES: We present preliminary results from a prospective multicentre study investigating the conservation of residual hearing after implantation with a standard-length Nucleus Contour Advance perimodiolar electrode array and the benefits of combined electrical and acoustic stimulation. MATERIAL AND METHODS: The subjects were 12 adult candidates for cochlear implantation recruited according to national selection criteria. A "soft" surgery protocol was defined, as follows: 1-1.2-mm cochleostomy hole anterior and inferior to the round window; Nucleus Contour Advance electrode array inserted using the "Advance-off-stylet" technique; and insertion depth controlled by means of three square marker ribs left outside the cochleostomy hole. These procedures had been shown to reduce insertion forces in temporal bone preparations. Variations in surgical techniques were monitored using a questionnaire. Pure-tone thresholds were measured pre- and postoperatively. Patients who still retained thresholds <90 dB HL for frequencies up to 500 Hz were re-fitted with an in-the-ear (ITE) hearing aid. Word recognition was tested in quiet and sentence perception in noise for the cochlear implant alone and in combination with an ipsilateral hearing aid. RESULTS: Hearing threshold level data were available for 12 patients recruited from 6 of the centres. Median increases in hearing threshold levels were 23, 27 and 33 dB for the frequencies 125, 250 and 500 Hz, respectively. These median increases include the data for two patients who had total loss of residual hearing due to difficulties encountered during surgery. "Cochlear view" X-ray images indicated that the depth of insertion varied between 300 and 430 degrees, despite modest variations in the length of the electrode inserted (17-19 mm). The insertion angle had some influence on the preservation of residual hearing at frequencies of 250-500 Hz. Six of the 12 patients retained sufficient hearing for effective use of an ipsilateral ITE hearing aid (< or = 80 dB HL at 125 and 250 Hz; < or = 90 dB HL at 500 Hz). Word recognition scores in quiet were improved from 10% to 30% with the cochlear implant plus ipsilateral hearing aid in 3 patients who had at least 3 months postoperative experience. Signal:noise ratio thresholds for sentence recognition were improved by up to 3 dB. Patients reported that they experienced greatly improved sound quality and preferred to use the two devices together.

Angel Ramos Macías

Papers

Preservation of residual hearing with cochlear implantation: how and why.