The importance of electrode location in cochlear implantation

Abstract

ObjectivesAs indications for cochlear implantation have expanded to include patients with more residual hearing, increasing emphasis has been placed on minimally traumatic electrode insertion. Histopathologic evaluation remains the gold standard for evaluation of cochlear trauma, but advances in imaging techniques have allowed clinicians to determine scalar electrode location in vivo. This review will examine the relationship between scalar location of electrode arrays and audiologic outcomes. In addition, the impact that surgical approach, electrode design, and insertion depth have on scalar location will be evaluated. Data Sources: PubMed literature review Review Methods: A review of the current literature was conducted to analyze the relationship between scalar location of cochlear implant electrode arrays and speech perception outcomes. Further, data were reviewed to determine the impact that surgical variables have on scalar electrode location.ResultsElectrode insertions into the scala tympani are associated with superior speech perception and higher rates of hearing preservation. Lateral wall electrodes, and round window/extended round window approaches appear to maximize the likelihood of a scala tympani insertion. It does not appear that deeper insertions are associated with higher rates of scalar translocation.ConclusionSuperior audiologic outcomes are observed for electrode arrays inserted entirely within the scala tympani. The majority of clinical data demonstrate that lateral wall design and a round window approach increase the likelihood of a scala tympani insertion.Level of EvidenceN/A.

The evaluation of a slim perimodiolar electrode: surgical technique in relation to intracochlear position and cochlear implant outcomes

“…While the exact explanation for the (CS associated) translocations in present paper remains unclear, based on the findings of this study and the reports in the literature, in favor of the RW approach rather than the CS [8,24], it was decided to convert our surgical approach for the SPE to the RW approach to ensure highest probability on the ST position. Extending the RW approach, which involves removal of the crista semilunaris and some of the anterior bony edge of the window with a diamond drill size 0.8 or even 0.6 mm, is necessary for the SPE to facilitate the insertion of the sheath of the insertion tool.…”

“…The fact that all translocations in our study were located directly at the CS site indicates a correlation with the used surgical technique. This hypothesis is strengthened by two studies [8,24] with a large number of participants (n = 116 and n = 220); in which it was reported that a CS approach, compared to an (extended) RW approach, is associated with higher risk of translocation, independent of the implanted conventional electrode type. Our study is the first to report CS associated translocations for the slim, perimodiolar electrode, which was designed to be nontraumatic with any surgical approach [13].…”

Surgical anatomy of the round window—Implications for cochlear implantation

“…When trying to keep the RWM intact, the direction of drilling on the promontory is recommended to come from the bottom (hypotympanum) upwards, thus opening the cochlea from its underside, as otherwise the basilar membrane may be damaged or even the SV opened . There is mounting evidence suggesting that electrode location inside the cochlea is of importance as electrode insertions into the ST (compared to SV or interscalar excursion from ST to SV) are associated with superior speech perception and higher rates of hearing preservation …”

“…36 There is mounting evidence suggesting that electrode location inside the cochlea is of importance as electrode insertions into the ST (compared to SV or interscalar excursion from ST to SV) are associated with superior speech perception and higher rates of hearing preservation. 28,29,49 Interestingly, if the determination of surgical approach (cochleostomy, RW or extended RW) is left to the discretion of the surgeon, then over a period of time the RW approach becomes preferred and is utilised more frequently. 30 Knowing the orientation of the cochlea and hence, the course of the cochlear turns is a prerequisite for RW insertion.…”

Investigating variability in cochlear implant electrode array alignment and the potential of visualization guidance

“…However, scalar crossing into the scala vestibuli (SV) and other intracochlear trauma may occur with forces at or below the limit of force perception by hand . In addition, placement of the EA close to the modiolar wall has been shown to reduce excitation thresholds and lead to better hearing outcomes . Placement of PEAs requires skill in choosing the access point into the ST and in aligning the pre‐bent EA accurately with the natural bend of the cochlear basal turn.…”