Implication of Bony Cochlear Nerve Canal on Hearing in Patients with Congenital Unilateral Sensorineural Hearing Loss

Abstract

This study was designed to evaluate the dimensions of the bony cochlear nerve canal (BCNC) in congenital unilateral sensorineural hearing loss (USNHL) patients with normal inner ears, and to analyze the correlation between BCNC and hearing status. Medical records and temporal bone computed tomography (TBCT) findings of 380 patients who visited Seoul National University Hospital between January 1999 and December 2007 were reviewed retrospectively. The length and width of the BCNC at the fundus of the internal auditory canal were measured in millimeters based on the axial view of TBCT for three ear groups: normal inner ears of control group subjects (group A, 179 ears), normal inner ears on the contralateral side of USNHL patients (group B, 201 ears), and the affected inner ears in USNHL (group C, 201 ears). The mean values of length and width in group C (0.79 ± 0.36 and 1.58 ± 0.83 mm, respectively) were significantly smaller than those in group A (1.07 ± 0.10 and 2.38 ± 0.28 mm, respectively; p < 0.001) and group B (1.04 ± 0.23 and 2.33 ± 0.39 mm, respectively; p < 0.001). The receiver operating characteristic curves for BCNC were conducted to estimate the cutoff values from which the proportions of profound hearing loss increased, compared to those of mild to severe hearing loss. The areas under the curve were 0.487 ± 0.044 (p = 0.781) and 0.622 ± 0.041 (p = 0.011) for length and width, respectively. The cutoff value of width with a sensitivity of 90% for profound USNHL was 1.16 mm in otherwise normal inner ears. Clinicians would be recommended to take a close look at BCNC as one of the possible causes of hearing loss in otherwise normal inner ears of USNHL on TBCT.

Does the Width of the Bony Cochlear Nerve Canal Predict the Outcomes of Cochlear Implantation?

“…In a previous study, we evaluated the BCNC length and width in normal inner ears: 1.07 mm and 2.38 mm, respectively. In cases of congenital unilateral sensorineural hearing loss, the BCNC length and width in affected inner ears were significantly smaller than those in normal inner ears [ 1 ]. The mean width in the affected inner ears in our previous study was 1.58 mm; other investigators have reported mean widths of 1.12 mm and 1.0 mm [ 10 , 11 ].…”

“…Previous research has suggested that the lower limit of normal BCNC width is 2.10 mm; this was obtained by subtraction of the standard deviation from the mean value in normal hearing inner ears [ 1 ]. Thus, the mean BCNC width in normal patients is higher than 2.0 mm.…”

“…BCNC stenosis was defined as a BCNC width less than 1.4 mm, as reported in a previous study [ 2 ]. When the BCNC was greater than 2.0 mm in diameter, it was defined as having a normal size, as described in previous research [ 1 ]. Children in this study were divided into three groups based on the BCNC width: Group 1 (<1.4 mm, n = 17), Group 2 (1.4–2.0 mm, n = 14), and Group 3 (>2.0 mm, n = 25).…”

“…The bony cochlear nerve canal (BCNC) lies between the fundus of the internal auditory canal (IAC) and the base of the cochlea. It encases the cochlear nerve fibers from the spiral ganglion to the cochlear nerve [ 1 ] ( Figure 1 ). Therefore, a narrow BCNC likely indicates anatomic or functional deficiency in the cochlear nerve.…”

Prediction of Cochlear Implant Outcomes in Patients With Prelingual Deafness

“…Using the bony cochlear nerve canal (BCNC) evaluation system developed by Fatterpekar et al [10], relationships between BCNC parameters and both hearing level and the presence of the cochlear nerve were established [11]. In our study, the width of the BCNC at the fundus of the internal auditory canal was determined in axial slices of temporal bone computed tomography images, at the point where it was maximal in contiguous sections, by measuring the distance between the inner margins of the bony wall at the mid-portion.…”