Combined electric and acoustic stimulation (EAS) of the auditory system is a new therapy for patients with severe to profound high- and mid-frequency hearing loss but remaining low-frequency hearing. In a prospective study, 13 patients with low-frequency hearing of better than 60 dB below 1 kHz were implanted with a MED-EL COMBI 40+ cochlear implant. Pure tone thresholds as well as monosyllabic word scores and Hochmair-Schulz-Moser sentences in quiet and in noise were measured with hearing aids, cochlear implant alone and in the combined stimulation mode (EAS) in the same ear. Hearing could be partially preserved in 11 out of the 13 patients. All patients scored significantly higher with cochlear implant alone than with hearing aids. Seven patients scored higher in the EAS mode than with cochlear implant alone for sentences in noise, 4 remained unchanged, and 2 could not use EAS. Synergistic effects of EAS were most prominent for hearing in noise with increases of up to 72% as compared to cochlear implant alone.

This study reports successful conservation of hearing after cochlear implantation using a modified surgical technique. Even high levels of hearing could be maintained, showing that implantation of an intracochlear electrode can be performed atraumatically with preservation of functional structures.

Preservation of low-frequency hearing in cochlear implantation is possible in patients implanted because of profound high-frequency deafness. With the development of new, more atraumatic electrode designs, preservation of residual hearing should be further improved.

Insertions through the round window membrane were shown to be atraumatic, even in basal cochlear regions. This route of insertion might be very effective for combined electric and acoustic stimulation of the auditory system.

The Hearing Preservation Classification System proposed herein fulfills the following necessary criteria: 1) classification is independent from users' initial hearing, 2) it is appropriate for all cochlear implant users with measurable pre-operative residual hearing, 3) it covers the whole range of pure tone average from 0 to 120 dB; 4) it is easy to use and easy to understand.

Results showed that some degree of hearing preservation was possible in 15718 patients. All subjects showed statistically significant benefit on all three speech perception tests over time. These significant benefits were also reflected in the subjective benefit outcomes.

Objective: The objective of this study was to assess the intracochlear position and the extent of trauma to cochlear structures using a new prototype electrode carrier (Flex EAS). Special emphasis was placed on the practicality for combined electric and acoustic stimulation of the auditory system. Study Design: Human temporal bones were evaluated histologically after insertion of the electrodes, and insertion forces were measured in an acrylic model of the scala tympani. Methods: 1) Insertion forces with the regular C40؉ array and the new electrode prototype were measured in an acrylic model of the scala tympani. 2) Ten human temporal bones were implanted using the same surgical procedure as in vivo. All bones underwent fixation methylmethacrylate embedding to allow cutting of the undecalcified bone with the electrode in situ. In addition, radiography of the implanted devices was performed and correlated to histologic results. Electrode positions and trauma to cochlear structures were then evaluated histologically. Results: All insertions of the new electrode array were performed in the scala tympani of the cochlea. All insertions were atraumatic and covered one cochlear turn. The only effect on cochlear structures that could be observed was a slight lifting of the basilar membrane in the middle turn limited to the tip of the electrode. In three bones, basal trauma, which resulted from the cochleostomy itself, could be observed as well. All neural structures remained intact. Conclusions: The new electrode prototype provides very good mechanical properties for safe and atraumatic implantation. All criteria for the use in hearing-preservation cochlear implantation for electric and acoustic stimulation were fulfilled. Surgical measures to prevent basal trauma appear to be very important.

Hearing preservation was achieved in all patients (complete preservation 44.44%) after a mean follow-up period of 9.73 months. Mean monosyllabic test scores improved from 9% correct with the hearing aid alone to 48% with the cochlear implant and to 65% in the electric-acoustic mode.