Objectives: Malformations of the inner ear account for approximately 20% of cases of congenital deafness. In current practice, straight arrays with circumferential electrodes (i.e., full-banded electrodes) are widely used in severely malformed cochleae. However, the unpredictability of the location of residual spiral ganglion neurons in such malformations argues against obligatorily using full-banded electrodes in all cases. Here, we present our experience of electrically evoked compound action potential (ECAP) and radiography-based selection of an appropriate electrode for severely malformed cochleae.
Methods: Three patients with severely malformed cochleae, showing cochlear hypoplasia type II (CH-II), incomplete partition type I (IP-I), and cochlear aplasia with a dilated vestibule (CADV), respectively, were included, and the cochlear nerve deficiency (CND) was evaluated. A 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 a lateral wall electrode (CI422), revision CI was performed due to incomplete insertion of CI422 and resultant unsatisfactory performance by 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' auditory performance markedly improved postoperatively.
Conclusion: The ECAP and radiography-based strategy to identify an appropriate electrode may be useful for severely malformed cochleae, leading to enhanced functional outcomes. The practice of sticking to full-banded straight electrodes may not always be optimal for IP-I and CH-II.
Keywords: Cochlea; Cochlear Implantation; Congenital Abnormalities; Electrodes.