Olfactory bulb volume in cochlear implant candidates as compared to age-matched control subjects: A potential marker of cognitive function for auditory information processing.

Abstract

To evaluate magnetic resonance imaging (MRI)-based olfactory bulb (OB) volumes in cochlear implant (CI) candidates with sensorineural hearing loss as compared to age-matched control subjects with normal hearing. A total of 31 pediatric CI candidates (mean±SD age: 7.0±2.5 years, 51.6% were boys) with sensorineural hearing loss and 35 age-matched control subjects (mean±SD age: 7.1±2.5 years, 54.3% were boys) with normal hearing were included in this study. Data on demographic characteristics (age, gender) and right and left OB volume (mm3) on MRI using planimetric contouring method were recorded in patients and control groups. Median (min-max) values for right OB volume (80(50-120) vs. 90(50-160) mm3, p=0.006) and left OB volume (70(50-120) vs. 90(50-170) mm3, p=0.007) were significantly lower in CI candidates vs. controls, regardless of the gender and age. No significant difference was noted between right and left OB volume in CI candidate and control groups. Hearing loss subgroups of CI candidates including hereditary familial (n=8), hereditary non-familial (n=14) and mixed syndromic (9) subgroups were also similar in terms of patient demographics and OB volumes. There was a tendency for having lower left OB volume (60(50-120) vs. 80(60-110) mm3) in girls vs. boys in the CI candidate group, along with a tendency for lower left and right OB volume in candidates vs. controls, particularly at age 11 (median 120 vs. 80mm3 and 120 vs. 60mm3, respectively). No significant correlation of age was noted with right and left OB volume overall and in the study groups. In conclusion, our findings revealed lower left and right OB volumes in CI candidates compared to control subjects, regardless of age and gender, indicating the presence of baseline olfactory dysfunction in patients with hearing loss planned to undergo CI. Accordingly, MRI-based measurement of OB volume in the pre-surgical workup of CI candidates may serve as a marker of cognitive function enabling auditory information processing that may also correlate with post-operative CI outcomes.