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Original Article |

Correlation of Cochlear Nerve Size and Auditory Performance After Cochlear Implantation in Postlingually Deaf Patients

Bo Gyung Kim, MD; Hyo Jin Chung, MD; Jeong Jin Park, MD; Sera Park, MD; Sung Huhn Kim, MD, PhD; Jae Young Choi, MD, PhD
JAMA Otolaryngol Head Neck Surg. 2013;139(6):604-609. doi:10.1001/jamaoto.2013.3195.
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Importance Cochlear implantation (CI) yields outstanding results in postlingual deafness, but outcomes of auditory performance after CI are variable. Thus far, it has been difficult to accurately predict patient prognoses after CI.

Objective To assess whether cochlear nerve (CN) size as measured with parasagittal magnetic resonance imaging (MRI) is correlated with auditory performance after CI in postlingually deaf patients.

Design Retrospective study. All MRI results were reviewed by the same observer, who was blinded to the participants' information.

Setting A university tertiary care center.

Participants All 102 postlingually deaf adults who underwent CI during the period August 2010 through June 2012 were eligible to participate. Thirty-four patients were excluded because MRI was not performed or was not of sufficient quality for assessment. Sixty-eight postlingually deaf adults (mean [range] age, 49 [16-77] years) were enrolled.

Exposure Cochlear implantation.

Main Outcomes and Measures Size of the CN and auditory performance.

Results The mean (SD) cross-sectional area (CSA) of the CN was 0.922 (0.229) mm2 and tended to decrease with age; however, there was no significant correlation between the size of the CN and age. The cause of deafness also did not affect the size of the CSA. However, CSA was negatively associated with both the duration of deafness (P < .001) and degree of hearing loss (P = .008 for the difference in CSA between ears with no more than 80-dB hearing loss [n = 25] and ears with at least 101-dB hearing loss [n = 65]). Interestingly, CSA was positively correlated with auditory performance after CI (P = .04).

Conclusions and Relevance We suggest that measuring the size of the CN with parasagittal MRI can yield information that is helpful in preoperative counseling of patients.

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Figures

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Figure 1. Measurement of cross-sectional area of the cochlear nerve. A, Parasagittal images acquired from axial images (dotted line, cut line of 3-dimensional–driven equilibrium sequence; solid line, middle of the measured internal auditory canal). B, Parasagittal images of the internal auditory canal. The vertical and horizontal diameters were measured with calipers.

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Figure 2. Scatterplots. A, Correlation between age and the cross-sectional area (CSA) of the cochlear nerve. Linear regression analysis showed a negative correlation between age and the CSA (slope = −0.00199). Pearson correlation coefficient, 0.143; P = .10. B, Correlation between the duration of deafness and the CSA of the cochlear nerve. Linear regression analysis showed a negative correlation between the duration of deafness and CSA (slope, −0.00724). Pearson correlation coefficient, −0.511; P < .001.

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Figure 3. Cross-sectional areas of the cochlear nerves in 5 patients who had different durations of deafness in each ear. The numbers in parentheses indicate the duration of deafness in years.

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Figure 4. Parasagittal images showing the internal auditory canals in the ears that had been deaf for 1 year (cross-sectional area [CSA], 1.173 mm2) (A) and 10 years (CSA, 0.769 mm2) (B). The arrows indicate the cochlear nerves.

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Figure 5. Cross-sectional area of the cochlear nerve. The number above each box represents the number of ears in the sample. The box indicates SD; inside the box, the horizontal line indicates the median and the small rectangle indicates the mean; X indicates 1% and 99% of the range. A, Patients with sensorineural hearing loss. The patients' ears were divided into 5 groups according to the level of hearing loss. B, Patients with deafness due to various causes. S-SNHL, sudden sensorineural hearing loss; COM, chronic otitis media.

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Figure 6. Correlation between auditory-only (AO) sentence test scores and cross-sectional area (CSA). A, Pre–cochlear implantation (CI) test scores (slope, 0.00162). Pearson correlation coefficient, 0.155; P = .15. B, (Post-CI –Pre-CI) test scores (slope, 0.00096). Pearson correlation coefficient, 0.142; P = .19. C, Post-CI test scores (slope, 0.00131). Pearson correlation coefficient, 0.216; P = .04.

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