Assessment of the contralateral routing of signal system in unilateral cochlear implantation

The purpose of this study was to evaluate the contribution of a contralateral routing of signal (CROS) system in unilateral cochlear implants (CI) users.

Single-centre prospective interventional study.

Tertiary referral centre.

Eight unilateral cochlear implants patients with >30% speech perception in silence and >6 months' implantation.

Free-field speech perception assessed by 'vowel-consonant-vowel' pseudoword test and free-field spatial localisation by Fournier lists on five loudspeakers (in silence and in noise). Subjective benefit assessed on the abbreviated profile of hearing aid benefit (APHAB) questionnaire. These tests were performed on the 1st and 15th day of the trial (denoted by D1 and D15, respectively).

Contralateral routing of signal-cochlear implants provided significant improvement in speech perception at D1 and D15 in silence (P, respectively, 0.03 and 0.025) and in noise (P 0.012 and 0.036). No improvement in spatial localisation was demonstrated. The abbreviated profile of hearing aid benefit quality of life questionnaire administered at D15 showed overall benefit and a significant difference in ease of communication with versus without contralateral routing of signal. By 6 months, however, 75% of the patients (6/8) had abandoned the system due to trouble in noise (5/6), trouble with the device's wiring (3/6) and onset of headache (4/6).

Contralateral routing of signal-cochlear implants is an interesting novel option, restoring a binaural effect and providing improved speech perception and non-negligible comfort of hearing in certain patients, without the medical and economic costs of bilateral cochlear implants. However, the drawbacks (especially the difficulty of modulating the signal-to-noise ratio) do not presently allow it to be an effective alternative to bilateral cochlear implants.