Characteristics of Medial and Lateral Wall Cochlear Implant Arrays Demonstrated with Cone Beam CT and Evoked Electrical Auditory Brainstem Responses

HYPOTHESIS: This study investigates how electrode array types-straight versus perimodiolar-affect cochlear implant (CI) placement (i.e., modiolar proximity and angular depth) and outcomes using cone beam computed tomography (CBCT) and evoked electrical auditory brainstem responses (eABR).

BACKGROUND: Cochlear implants (CIs) have revolutionized auditory rehabilitation, yet optimizing electrode placement remains crucial for improving speech perception and pitch discrimination. Array designs influence electrode proximity to neural structures, impacting neural stimulation efficacy.

METHODS: We analyzed 108 patients using CBCT to compare straight and perimodiolar electrode arrays (each with 22 electrodes) in terms of angular depth, spiral diameter, intracochlear positioning index (ICPI), electrode to modiolus, medial-lateral distance (EMML), and wrapping factor. A subset of 50 patients underwent eABR assessments across cochlear regions.

RESULTS: Significant differences were found between array types. Straight arrays showed less variability with consistent lateral placement compared to perimodiolar arrays. Measurements revealed differences: wrapping factor (M = 0.692 vs. 0.826; t(11) = 8.104, p = 0.000), angular depth (M = 351.2° vs. 437°; t(11)=4.527, p = 0.000), spiral diameter (M = 3.24 mm vs. 5.027 mm; t(11)=11.1, p = 0.000), and modified ICPI (M = 0.628 vs. 0.783; t(11)=9.742, p = 0.000). eABR results showed larger average amplitudes with straight arrays in basal and mid regions (p < 0.05), suggesting potentially enhanced neural stimulation and a more focused stimulation with perimodiolar arrays.

CONCLUSION: Our findings underscore the importance of electrode array type in CI outcomes, emphasizing the need for precise positioning to optimize neural stimulation and clinical outcomes. Personalized array selection based on CBCT assessments may lead to improved speech perception, pitch discrimination, and overall auditory function. Future research should aim to refine stimulation strategies to maximize CI benefits, particularly where direct measurements strongly correlate with clinical outcomes compared to derived measurements.