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

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Abstract

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 1.4 mm 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, R2 = 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 1.4 mm, pure tone audio averages were more than 70 dB HL in most ears.

Introduction

Conventional temporal bone computed tomography (TBCT) is widely performed for detecting inner ear anomalies, such as incomplete partitions, common cavity, cochlear aplasia, cochlear hypoplasia, and complete labyrinthine aplasia (Michel deformity) [1], [2]. In many sensorineural hearing loss (SNHL) cases, however, such anomalies are often not identified.

Recently, with improvement in imaging quality, some authors have reported previously unrecognized anomalies including internal auditory canal anomaly, bony cochlear nerve canal (BCNC) anomaly and other vestibular anomalies [1], [3], [4]. In particular, BCNC stenosis may be the anatomic cause of congenital SNHL in the absence of cochlear malformation [1], [2], [3], [4], [5]. Few reports have been published on the diameter of the BCNC in unilateral SNHL patients despite of its importance. Thus, we evaluated the diameter of the BCNC in patients with congenital unilateral SNHL using high-resolution TBCT and established a standard measure for diagnosing stenosis of the BCNC with audiologic evaluation.

Section snippets

Participants

We retrospectively evaluated 51 unilateral SNHL patients (27 boys, 24 girls) aged 0–18 years (mean age 11 years) who underwent 0.6 mm thickness high-resolution TBCT between 2006 and 2010. This retrospective study was approved by the Institutional Review Board of Asan Medical Center and for data collection and analysis, and informed consent was waived. Patients with non-syndromic unilateral SNHL confirmed by a pure tone audiogram (PTA) or auditory brainstem response (ABR) (normal ear  25 dB, SNHL

Results

The mean width of the BCNC was 2.15 ± 0.75 mm (±2 standard deviations [SD]) on axial images in normal hearing ears, and 1.21 ± 0.53 mm (±2 SD) in SNHL ears. BCNC stenosis (<1.4 mm, −2 SD below the mean) was observed in 29 of 51 patients (57%) in the SNHL ears group but in only one patient with normal ears (Fig. 2). The 1 patient who had BCNC stenosis (1.15 mm) in the normal ear group showed BCNC atresia in the SNHL ear side. Complete atresia of BCNC was observed in 4 out of 51 patients in SNHL ears.

Discussion

Only a few reports have been published about the inner ear anomalies in unilateral SNHL, and it is not known which anomalies are common in unilateral SNHL [1]. Recently, many groups have attempted to use high-resolution TBCT to detect other inner ear anomalies in SNHL patients, such as enlarged vestibular aqueduct syndrome and BCNC stenosis [1], [3], [6], [7], [8]. The BCNC is defined as a bony transition point between the IAC and the cochlear modiolus that carries the cochlear nerve fibers.

Conclusions

The findings of the present study suggest that the diameter of the BCNC was significantly narrower in ears with unilateral SNHL than in normal ears. We suggest a mean value <1.4 mm on axial images from TBCT to indicate BCNC stenosis. IAC stenosis and cochlear hypoplasia were significantly associated with BCNC stenosis. These patients showed severe to profound hearing loss in almost all cases.

Conflict of interest

The authors have no financial disclosure or conflicts of interest.

Financial disclosure

None.

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