A case of mixed hearing loss due to inner ear malformation that resembled incomplete partition type Ⅲ

Abstract

We herein report a case of inner ear malformation similar to incomplete partition type Ⅲ (IP-3). A 7-year-old boy with mixed hearing loss had been wearing hearing aids since 9 months of age. His mother and younger twin sister also wore hearing aids. His parents consulted an otolaryngologist requesting cochlear implantation. Pure tone audiometry revealed that the patient had an air-conduction threshold of 100 dB bilaterally, but the bone-conduction threshold was 25-50 dB. The aided threshold was 35-45 dB. The patient was not indicated for surgery for cochlear implantation and was instead offered a thorough examination to seek out the underlying cause of his mixed hearing loss. However, the parents refused additional tests. The patient was then referred to the authors' department, again requesting cochlear implantation. Computed tomography and magnetic resonance imaging of the temporal bone reveraled that bony density of the otic capsule was low, modiolus was absent, and the cochleae were directly connected to the internal acoustic canals. This imaging feature indicated that the patient had an inner ear anomaly of IP-3. Patients with IP-3 who have residual serviceable hearing are recommended not to undergo cochlear implantation. Otolaryngologists who treat deaf children should be aware of the different mechanisms underlyng hearing loss due to different causes, and should be able to explain these mechanisms to patients' parents as simply as possible.