Role of Electrode Placement as a Contributor to Variability in Cochlear Implant Outcomes

Abstract

Hypothesis Suboptimal cochlear implant (CI) electrode array placement may reduce presentation of coded information to the central nervous system and consequently limit speech recognition. Background Generally, mean speech reception scores for CI recipients are similar across different CI systems, yet large outcome variation is observed among recipients implanted with the same device. These observations suggest significant recipient-dependent factors influence speech reception performance. This study examines electrode array insertion depth and scalar placement as recipient-dependent factors affecting outcome. Methods Scalar location and depth of insertion of intracochlear electrodes were measured in 14 patients implanted with Advanced Bionics electrode arrays and whose word recognition scores varied broadly. Electrode position was measured using computed tomographic images of the cochlea and correlated with stable monosyllabic word recognition scores. Results Electrode placement, primarily in terms of depth of insertion and scala tympani vs. scala vestibuli location, varies widely across subjects. Lower outcome scores are associated with greater insertion depth and greater number of contacts being located in scala vestibuli. Three patterns of scalar placement are observed suggesting variability in insertion dynamics arising from surgical technique. Conclusion A significant portion of variability in word recognition scores across a broad range of performance levels of CI subjects is explained by variability in scalar location and insertion depth of the electrode array. We suggest that this variability in electrode placement can be reduced and average speech reception improved by better selection of cochleostomy sites, revised insertion approaches, and control of insertion depth during surgical placement of the array.

Automated analysis of human cochlea shape variability from segmented μ CT images

“…The classical implantation procedure involves drilling a path through the mastoid in order to reach the tympanic cavity allowing the surgeon to open the scala tympani (one of the three cochlear ducts) and insert an electrode array. The functional outcomes for these subjects are linked to the potential insertion traumas (Aschendorff et al, 2007;Finley et al, 2008). The insertion can lead to lesions of the modiolus, osseous spiral lamina or basilar membrane, resulting in degeneration of the ciliated (Adunka et al, 2004) and spiral ganglion cells (Leake et al, 1999).…”

Switching off Electrodes in Cochlear Implants - Causes and Consequences

“…With the advancement of imaging techniques, recent studies have shown that this event of displacement of the electrode array from the tympanic to the vestibular ramp is more frequent than thought and may be a reason for less favorable auditory performance in several patients. The cochleae do not all have the same shape and dimension whereby the (3) electrode array chosen for an implanted patient should be considered in an individualized manner [10,11,12].…”

Standardization of CT Depiction of Cochlear Implant Insertion Depth

“…1 It is important to be able to describe the CI tip location because electrode-array insertion depth and location are relevant factors when considering hearing and speech outcomes following CI insertion. [1][2][3][4] Audiologic outcomes are better when the electrode array is inserted into the scala tympani, allowing better stimulation of the spiral ganglion neural elements. Multidetector CT can detect the scala tympani in cadaveric specimens, 5 but application to routine clinical postimplantation imaging is limited.…”