Interaural correlation of acoustic hearing preservation following sequential cochlear implantation

Compared to unilateral cochlear implantation, bilateral cochlear implantation demonstrates multiple advantages in speech understanding in noise and sound localization, especially when acoustic hearing is preserved in both ears. However, outcomes and factors influencing acoustic hearing preservation following cochlear implant (CI) remains poorly understood. Patients receiving sequential cochlear implantation are a valuable population to investigate as studying bilateral ears allows for a high degree of control of individual factors that may be affecting trends in hearing.

This is a retrospective analysis of prospectively collected data. Twenty-three subjects met criteria for CI with residual hearing, defined as low frequency (LF) pure tone average (PTA) of 65 dB or less at 125, 250, and 500 Hz, and received sequential cochlear implantation were included in the study. Audiometric data was collected on all subjects pre/post-operatively. Speech perception was assessed in everyday listening conditions pre/post-implantation using CNC and AzBio materials.

Bilateral hearing preservation was achieved in 56.5% (13/23) of patients. Of the 16 patients with hearing preservation following the first implant, 81% (13/16) of them achieved bilateral hearing preservation following the second implant in the contralateral ear. Speech understanding scores improved after sequential cochlear implantation (p = 0.019). There was no significant correlation between length of electrode array and LFPTA in either ear (p = 0.464 and p = 0.699). About half (49%) of subjects retained functional acoustic hearing in the initially implanted ear 11 years post-implantation. There was significantly decreased retention rate of hearing preservation in the second ear (p = 0.014). Age at implantation overall significantly associated with loss of hearing preservation (p = 0.040).

Hearing preservation following sequential cochlear implantation improved everyday listening abilities despite greater loss of acoustic hearing in the sequentially implanted ear. Age at implantation was the only factor observed to correlate with hearing preservation over time. Given known histopathological evidence of inflammation following cochlear implantation, it is likely that an immune mediated process may be responsible for delayed and greater loss of hearing in the sequentially implanted ear. Therefore, individuals receiving sequential cochlear implantation are an excellent population in future studies investigating the inflammatory and immunomodulatory mechanisms that may be responsible for delayed hearing loss following cochlear implantation.