Potential implications of slim modiolar electrodes for severely malformed cochlea: A comparison with the straight array with circumferential electrodes.

Objectives: Malformations of the inner ear account for approximately 20% of congenital deafness. In current practice, the straight arrays with circumferential electrodes (i.e., full-banded electrodes) are widely used in severely malformed cochlea. However, the unpredictability of the location of residual spiral ganglion neurons in such malformations argues against obligatorily pursuing the full-banded electrode in all cases. Here, we present an experience of electrically evoked compound action potential (ECAP) and radiography-based selection of an appropriate electrode for severely malformed cochlea.
Methods: Three patients with the severely malformed cochlea, showing cochlear hypoplasia type II (CH-II), incomplete partition type I (IP-I), and cochlear aplasia with a dilated vestibule (CADV), were included, and the cochlear nerve deficiency (CND) was evaluated. Full-banded electrode (CI24RE(ST)) and slim modiolar electrode (CI632) were alternately inserted to compare ECAP responses and electrode position.
Results: In patient 1 (CH-II with CND) who had initially undergone cochlear implantation (CI) using the lateral wall electrode (CI422), a revision CI was performed due to incomplete insertion of CI422 and resultant unsatisfactory performance, thus explanting the CI422 and re-inserting the CI24RE(ST) and CI632 sequentially. Although both electrodes elicited reliable ECAP responses with correct positioning, CI24RE(ST) showed overall lower ECAP thresholds compared to CI632; thus, CI24RE(ST) was selected. In patient 2 (IP-I with CND), CI632 elicited superior ECAP responses relative to CI24RE(ST), with correct positioning of the electrode; CI632 was chosen. In patient 3 (CADV), CI632 did not elicit an ECAP response while meaningful ECAP responses were obtained with the CI24RE(ST) array once correct positioning was achieved. All patients markedly improved auditory performance postoperatively.
Conclusion: ECAP and radiography-based strategy for an appropriate electrode may be useful for severely malformed cochlea, leading to enhanced functional outcomes. Additionally, the practice of sticking to the full-banded straight electrode may not always be the best for IP-I and CH-II.