Comparison of Round Window and Cochleostomy Approaches with a Prototype Hearing Preservation Electrode

Abstract

Introduction: Preservation of residual hearing in cochlear implant recipients has been demonstrated to be possible and provides the potential benefit of combined electric and acoustic auditory stimulation. A prototype 16-mm multichannel array has been designed to facilitate placement of 22 electrodes without damage to intracochlear structures. The electrode array is suitable for insertion via the round window membrane (RWM) or a small cochleostomy. Aim: To evaluate the insertion trajectory and the presence of trauma to intracochlear structures with the prototype electrode inserted by either the RWM or a scala tympani cochleostomy. Materials and Methods: Eighteen fresh frozen human temporal bones were prepared for cochlear implantation using a standard transmastoid facial recess technique. Twelve electrodes were implanted at the University of Melbourne and 6 at the Medizinische Hochschule Hannover. In Melbourne fluoroscopy was used to monitor the insertions. Twelve prototype electrodes were inserted via the RWM. A further 6 electrodes were inserted via a small scala tympani cochleostomy. The cochleostomy was sited inferior to the RWM to avoid trauma to the basilar membrane and spiral ligament. Specimens were embedded and fixed with acrylic resin and the cochleae then examined histologically at 200-µm intervals using a grinding and polishing technique. Results: Full insertion of the electrode was achieved without significant resistance in all RWM and cochleostomy specimens. In two RWM specimens fold-over of the electrode tip occurred, and in one specimen the electrode penetrated the spiral ligament to lie in an ‘endosteal ‘position. In one cochleostomy specimen the electrode was rotated within the cochlea to face laterally rather than towards the modiolus. The final electrode position differed for the two groups, with the electrodes inserted via the RWM lying in a more perimodiolar position along the first part of the basal turn. The average depth of insertion was 240° for the RWM electrodes and 255° for the cochleostomy electrodes. Histologic examination showed no damage in any specimen to the modiolus, osseous spiral lamina or basilar membrane. Conclusions: A prototype hearing preservation electrode array was inserted by either a RWM or a scala tympani cochleostomy without evidence of significant intracochlear trauma.

Cochlear Implants: System Design, Integration, and Evaluation

“…To maximize the flexibility in programming, most of these EAS electrodes retain the same number of stimulating contacts found in the corresponding standard length electrodes in regular cochlear implants. Temporal bone studies using these shortened electrodes indicate that they can be introduced without damage and human trials have shown that subjects implanted with these electrodes experience a smaller average increase in acoustic threshold than is seen with full length electrodes in similar subject populations [134][135][136][137].…”

Radiological Dehiscence of the Mastoid Portion of the Facial Nerve after Posterior Tympanotomy: Does It Lead to Increased Risk of Nerve Injury?

“…The drilling required occurs very close to the chorda tympani-facial nerve angle, thus putting both nerves at risk. Although this should be possible with a thorough knowledge of anatomy, the same author has stated that many CI surgeons are not confident enough to perform complete facial recess dissection [13] . On the other hand, there is much evidence that an anterior cochleostomy can result in scala media or vestibuli insertions [14] .…”

Strategies to Improve Music Perception in Cochlear Implantees

“…Within this study, comparisons between long-term Hybrid-S users and long-term long array users who were matched on word understanding in quiet showed a difference in speech perception in noise (using both multi-talker babble and steady-state noise), suggesting that the Hybrid-S users perform better within a more realistic listening environment. Despite these benefits, Briggs and colleagues (Briggs et al, 2006) identified the possibility that shortening of the electrode array to 10mm may cause a place-frequency mismatch because only the basal portion of the cochlea will be stimulated, causing a disproportionately higher frequency percept than with a standard array. Further, should hearing not be preserved, then concerns have been raised that speech perception outcomes will be impaired for individuals who only receive electrical stimulation in such a limited region of the cochlea (Gstoettner et al, 2009).…”