Bilateral Electric Acoustic Stimulation: A Comparison of Partial and Deep Cochlear Electrode Insertion

Abstract

A patient with bilateral severe, sloping, high-frequency hearing loss was treated with sequential bilateral electric acoustic stimulation (EAS) using the MED-EL Duet EAS cochlear implant. On one side, a partial 18-mm insertion of the electrode array (M-type) in the cochlea was performed. The contralateral side was implanted 39 months later with a deep 30-mm insertion of the electrode array (FLEX(soft) type). The aims were to assess whether low-frequency hearing could be preserved after deep electrode insertion, as well as to assess the benefit of bilateral EAS surgery compared to monaural EAS. Hearing thresholds and speech recognition outcomes were measured preoperatively and up to 48 months postoperatively. Outcomes from the partial and deep insertion side are compared. The benefit of EAS in daily life was assessed with the Abbreviated Profile of Hearing Aid Benefit questionnaire. Benefits of bilateral EAS were calculated from speech reception thresholds measured using the LINT speech-in-noise number test. Speech was always presented from the front. Noise was either presented from the front, from the left side, or from the right side. Each condition was measured for unilateral and bilateral EAS use. Partial as well as deep insertion of the electrode array resulted in hearing preservation and significant speech recognition in this particular case. Both EAS devices provided more than 80% speech recognition in noise at a 10-dB signal-to-noise ratio. Bilateral EAS was beneficial for speech reception in noise compared to monaural EAS. A head shadow effect of 3.4 dB, binaural squelch effect of 1.2 dB and binaural summation effect of 0.5 dB were measured. Hearing preservation is also possible after cochlear implantation using a FLEX(soft) electrode array with a near-full insertion (30 mm) into the cochlea. Bilateral EAS was successfully implemented in this patient providing better speech recognition compared to monaural EAS.