Objective: To investigate the functional evaluation of auditory cortex by functional magnetic resonance imaging (fMRI) before cochlear implantation (CI).
Methods: Twenty-one children with severe to profound sensorineural hearing loss (SNHL) (7 cases with normal inner ear structure, 3 cases with large vestibular aqueduct syndrome, 1 case with cochlear nerve hypoplasia) and 7 children with normal hearing were examined by fMRI under sedation. The subjects received acoustic stimuli at four random frequencies (500, 1 000, 2 000, 4 000 Hz) during fMRI examination. Tones were interleaved with silence in a block-periodic fMRI design with 16-second on-off intervals.Each stimulus repeated twice and the total acquisition time was 4 minutes and 28 seconds.
Results: Activation was identified in the auditory cortex of the 28 subjects in response to monaural and binaural acoustic stimulation, which was shown in the transverse temporal gyrus (Heschl gyrus), the thalamus and both.Of the 21 patients with SNHL, contralateral dominance was shown in six cases, ipsilateral dominance in five cases and bilateral equilibrium in 10 cases when one ear was exposed to the stimuli. Of the seven children with normal hearing, contralateral dominance was shown in three cases, ipsilateral dominance in two cases and bilateral equilibrium in two cases.No significant difference of the activation intensity in auditory cortex was shown between children with SNHL and normal hearing (P > 0.05). Good hearing recovery was obtained in the 21 patients after CI. No significant difference in the level of hearing and speech rehabilitation was shown between children with LVAS and with normal inner ear structure.Listening behavior response threshold was 55 dBHL in the case with cochlear nerve hypoplasia 10 months after CI.
Conclusions: fMRI would be a feasible means of evaluating the function of the auditory cortex, which can be used for assessing the function of the entire auditory system prior to CI combined with ABR and imaging.