Proportion of bony cochlear nerve canal anomalies in unilateral sensorineural hearing loss in children.

OBJECTIVE: The aim of this study was to characterize the various bony anomalies of the inner ear in patients with unilateral sensorineural hearing loss using high-resolution temporal bone computed tomography and establish the relationship between hearing and the diameter of the bony cochlear nerve canal.

METHODS: We performed a retrospective review of 51 patients (mean age 11 years, range 0-20 years, 27 boys, 24 girls) who were diagnosed with unilateral sensorineural hearing loss with an audiogram. Coronal and axial diameter of the inner ear structures, including the internal auditory canal, bony cochlear nerve canal, and each turn of the cochlea and semicircular canals, were measured with high-resolution temporal bone computed tomography. The mean values (± 2 standard deviations) were calculated and compared between sensorineural hearing loss and normal ears, and between narrow bony cochlear nerve canal and normal bony cochlear nerve canal ears. Bony cochlear nerve canal atresia/stenosis was defined as a value less than 1.4mm in axial images.

RESULTS: The diameter of the bony cochlear nerve canal was significantly smaller in sensorineural hearing loss ears than in normal ears (p<.05). Associated inner ear anomalies, such as IAC stenosis (24%), cochlear hypoplasia (7-17%), and narrow semicircular canal bony island (8%) were only observed in the narrow bony cochlear nerve canal group. This group also showed statistically significant, severe to profound hearing loss compared to the normal bony cochlear nerve canal group (p<.05, R(2)=12.8%).

CONCLUSIONS: Most (57%) of the unilateral sensorineural hearing loss ears had bony cochlear nerve canal stenosis/atresia and this group showed associated inner ear anomalies. When the diameter of the bony cochlear nerve canal was less than 1.4mm, pure tone audio averages were more than 70 dB HL in most ears.