Management of Unilateral Hearing Loss in a 14-Year-Old with Internal Auditory Canal Duplication Using a Bonebridge Bone Conduction Implant.

BACKGROUND Duplicated internal auditory canal (dIAC) is a rare congenital temporal bone anomaly associated with ipsilateral sensorineural hearing loss (SNHL). The Bonebridge bone conduction implant has a magnet, an internal transducer, and an external audio processor. This report is of a 14-year-old girl with unilateral SNHL and vestibulocochlear nerve (VIII cranial nerve) aplasia due to dIAC who was treated with a Bonebridge bone conduction implant. CASE REPORT A 14-year-old girl was diagnosed with unilateral hearing loss during a school health check. Her hearing screening at birth was normal. Pure-tone audiometry revealed unilateral deafness in the right ear. CT scan showed a separate canal for the facial and vestibulocochlear nerves. MRI suggested unilateral aplasia of the right nerve VIII. The patient was implanted with a Bonebridge 602 implant in the right ear as a CROS (contralateral routing of signal). During implant activation in the Matrix test with the Bonebridge implant (in SSD configuration), the patient achieved SRT=-10.3 dB SNR. The results of the APHAB questionnaire indicated improvements in hearing. CONCLUSIONS Duplication of the internal auditory canal is pathognomonic for severe cochlear nerve hypoplasia or aplasia. It is important to perform an imaging study before deciding on implantation, as a hearing screening test at birth may not detect congenital hearing loss (embryogenesis of the inner ear and the internal auditory canal occurs independently). In the case of a unilateral anomaly with no hearing impairment on the opposite side, bone conduction implantation should be considered as a CROS.