Depth of Electrode Insertion and Postoperative Performance in Humans with Cochlear Implants: A Histopathologic Study

Abstract

The depth of electrode insertion of a multichannel cochlear implant has been suggested as a clinical variable that may correlate with word recognition using the implant. The current study evaluates this relationship using the human temporal bone collection at the Massachusetts Eye and Ear Infirmary. Twenty-seven temporal bones of subjects with cochlear implants were studied. Temporal bones were removed at autopsy, fixed and prepared for histological study by standard techniques. Specimens were then serially sectioned, and reconstructed by two-dimensional methods. Three measures of length were made from each subject’s reconstruction: (1) depth of insertion (DI) of the cochlear implant electrode array, from the round window to the array’s apical tip; (2) inserted length (IL) from the cochleostomy to the apical tip of the array, and (3) cochlear duct length (CDL) from the round window to the helicotrema. The active electrode length (AEL) was defined as the distance between the most apical and most basal electrodes of the array. Stepwise regression was used to identify whether subsets of six metrics associated with insertion depth (DI, DI/AEL, DI/CDL, IL, IL/AEL and IL/CDL), duration of deafness, sound-processing strategy, potential for central impairment and age at implantation accounted for significant across-subject variance in the last recorded NU-6 word score measured during each subject’s life. Age at implantation and potential for central impairment account for significant percentages of the across-subject variance in NU-6 word scores for the 27 subjects studied. None of the insertion metrics accounted for significant performance variance, even when the variance associated with the other variables was controlled. These results, together with those of previous studies, are consistent with a relatively weak association between electrode insertion depth and speech reception.

The Influence of Cochlear Implant Electrode Position on Performance

“…of deafness and preoperative phoneme and word scores, were significantly correlated with performance, both with phoneme and word scores. The outcomes of this study, performed in a large homogenous population, are in line with findings of Lee et al [2010], Gomaa et al [2003] and Finley et al [2008]. The variable age at implantation was also found to correlate with performance by Lee et al [2010], though in their study this relation disappeared after the elimination of 2 very good performers.…”

“…The outcomes of this study, performed in a large homogenous population, are in line with findings of Lee et al [2010], Gomaa et al [2003] and Finley et al [2008]. The variable age at implantation was also found to correlate with performance by Lee et al [2010], though in their study this relation disappeared after the elimination of 2 very good performers. Gomaa et al [2003] and Finley et al [2008] found duration of deafness and preoperative performance to be correlated with postoperative outcomes.…”

“…Nevertheless, several other studies [Hodges et al, 1999;Kos et al, 2005;Lee et al, 2010] did not find any correlation between speech perception performance and electrode position for several implant types. Moreover, the study by Gani et al [2007] reports on improvement of speech understanding after deactivation of apical electrodes in some patients with very deep insertions possibly to reduce pitch confusions among their most apical electrodes.…”

Is Electrode-Modiolus Distance a Prognostic Factor for Hearing Performances after Cochlear Implant Surgery?

“…Indeed, cochlear size demonstrates significant interindividual variability and induces heterogeneity in cochlear coverage in a population implanted with the same array [Lee et al, 2010]. Escudé et al [2006] suggested that the length of the cochlea can be estimated by 2 perpendicular measurements of the cochlear diameter in a plane parallel to the basal turn of the cochlea.…”

Abnormal Binaural Spectral Integration in Cochlear Implant Users

“…For a typical CI, the default range of frequencies analyzed can be as wide as 100-8,000 Hz. Due to its anatomical and design limitations, the electrode array is typically implanted to depths ranging from 8 to 21 mm (Lee et al 2010), corresponding to cochlear place frequencies of no lower than 500-1,500 Hz (Greenwood 1990). This leads to a severe tonotopic mismatch between the sound frequencies analyzed versus those actually stimulated electrically in the cochlea.…”