Congenital Internal Auditory Canal Stenosis

A 3-year-old boy underwent evaluation for possible cochlear implantation. He had failed a neonatal otoacoustic emission (OAE) hearing screen. A combined auditory brainstem response/auditory steady-state response (ABR/ASSR) test battery confirmed the presence of a severe hearing loss on the right and a profound hearing loss on the left. No Joint Committee on Infant Hearing (JCIH) risk factors for early childhood hearing loss1 were identified. Rehabilitation via hearing aid amplification and auditory-verbal speech therapy was unsuccessful. Computerized tomographic (CT) imaging of the temporal bone was performed to identify the presence of any inner ear abnormalities. No abnormalities of the cochlea, vestibule and semicircular canals on both sides were identified by the radiologist. The internal auditory canals were described as “fairly symmetrical without widening”, and the study was officially reported as an “unremarkable study of the temporal bones”. Independent review of the CT imaging revealed the presence of seemingly narrow internal auditory canals (IAC) on both sides. (Figure1A) The width of the IACs on the axial plane were measured by drawing a perpendicular line starting from the posterior wall of the IAC, 2 mm inside the posterior lip of the internal auditory meatus, and ending on the anterior canal wall, as described by McClay et al.2 Measurements taken utilizing the length measurement tool in the DICOM imaging software (RadiAnt DICOM Viewer, Version 2024.1, Medixant) indicated an IAC width of 1.78 mm on the right (with severe hearing loss) and 1.37 mm on the left (with profound hearing loss). (Figure 1B) These measurements confirmed the presence of bilateral internal auditory canal stenosis, a diagnosis defined by a canal of 2 mm or less on highresolution CT.3