Anatomy‐Based Frequency Allocation in Cochlear Implantation: The Importance of Cochlear Coverage

Abstract

Objectives/hypothesis This study aimed to compare the predicted anatomy‐based frequency allocation of cochlear implant electrodes with the default standard frequencies. Study Design Retrospective study. Methods A retrospective analysis was performed using computed tomography (CT) images of patients who received cochlear implants at a tertiary referral center. Patients were excluded if they had any congenital or acquired cochlear anatomical anomalies. The CT images of the patients were uploaded to the surgical planning software. Two independent reviewers allocated the anatomical parameters of the cochlea. The software then used these parameters to calculate the frequency allocation for each electrode according to the type of electrode and the length of the organ of Corti (OC) in each patient. These anatomy‐based frequency allocations were compared with the default frequency settings. Main Outcome Measure Frequency‐to‐place mismatch in semitones. Results A total of 169 implanted ears in 102 patients were included in this study. The readings of the two reviewers were homogenous, with a Cronbach's alpha of 0.98. The mean anatomy‐based frequency allocation was 487.3 ± 202.9 Hz in electrode 1; 9,298.6 ± 490.6 Hz in electrode 12. The anatomy‐based frequency allocations were found to be significantly higher than the frequencies of the default frequencies for each corresponding electrode (one‐sample t‐test, P < .001). The frequency‐to‐place mismatch was negatively correlated with cochlear coverage and positively correlated with the cochlear duct length (Pearson correlation > 0.65, P < .003). Conclusions The anatomy‐based frequency allocation of each electrode is significantly different from the default frequency setting. This frequency‐to‐place mismatch was affected mainly by the cochlear coverage. Level of Evidence 3 Laryngoscope, 132:2224–2231, 2022

Accuracy of Preoperative Cochlear Duct Length Estimation and Angular Insertion Depth Prediction

“…There is evidence for a positive correlation between an AID range within 630°to 720°(corresponding to a CC of 70% to 80%) and the postoperative speech perception (10,11,22). This effect is assumed to be related to a good match between the tonotopy of the cochlea and electrical stimulation by the CI electrode array (2,4,(6)(7)(8)(9)(23)(24)(25)(26)(27). Because the shape and size of the cochlea is unique in every CI recipient, patient-specific electrode array length selection is recommended to achieve the targeted AID range (3,6,10,21).…”

“…This effect is assumed to be related to a good match between the tonotopy of the cochlea and electrical stimulation by the CI electrode array (2,4,(6)(7)(8)(9)(23)(24)(25)(26)(27). Because the shape and size of the cochlea is unique in every CI recipient, patient-specific electrode array length selection is recommended to achieve the targeted AID range (3,6,10,21). Consequently, when using the approach of an individualized CC, an accurate prediction of AID before CI surgery is needed (4,7,9).…”

“…When applying the so-called anatomy-based fitting, the desired frequency map stimulation can be tuned to the natural cochlea map (2). It is assumed that this strategy may optimize the pitch match between the electrode array and the targeted neural structures in the cochlea and may lead to better speech perception (3)(4)(5)(6). Studies investigating different flexible lateral wall electrode arrays in CI surgery report an improved speech perception when higher insertion angles are achieved (7)(8)(9).…”

Morphologic Analysis of the Scala Tympani Using Synchrotron: Implications for Cochlear Implantation

“…[2][3][4][5][6][7] Reduced AID may reduce the frequency stimulation range and increase place-pitch mismatch within the cochlea. [8][9][10][11] However, there has been controversy regarding the ability to achieve high AID without causing scalar translocation, which has been associated with poor hearing outcomes and preservation. 9,12,13 Currently, the highest AID is achieved with 31.5 mm lateral wall electrodes which generally reach between 584 4 and 628 14 on average; however, some studies have found insertion depths past 720 .…”

One Click Is Not Enough: Anatomy-Based Fitting in Experienced Cochlear Implant Users

“…The main factor that creates the significant place-pitch differences is the position of the electrode array, which can be determined using high-resolution computed tomographic (CT) imaging and surgical planning software (3). Most publications thus far have retrospectively analyzed 1) the electrode-array insertion depth and place-frequency mismatch as a function of the array length, and 2) the correlation between mismatch and postoperative outcomes (1,(4)(5)(6). Therefore, because of these discrepancies mentioned within the previous literature, there is a need for a new fitting procedure to actively reduce the frequency to place mismatch.…”