Functional magnetic resonance imaging of hearing-impaired children under sedation before cochlear implantation

Abstract

Objective: To investigate functional magnetic resonance imaging (fMRI) in pediatric cochlear implantation candidates with residual hearing who are under sedation for evaluation of auditory function.

Design: During fMRI, subjects heard a random sequence of tones (250-4000 Hz) presented 10 dB above hearing thresholds. Tones were interleaved with silence in a block-periodic fMRI design with 30-second on-off intervals. Twenty-four axial sections (5 mm thick) covering most of the brain were obtained every 3 seconds for a total acquisition time of 5.5 minutes.

Setting: Single tertiary academic medical institution.

Patients: Severely to profoundly hearing-impaired children (n=10; mean age, 49.1 months). During fMRI, subjects were awake (n=2) or sedated with pentobarbital sodium if their weight was 10 kg or greater (n=4) or chloral hydrate if their weight was less than 10 kg (n=4).

Main outcome measures: Detection of brain activation by fMRI in the primary auditory cortex (A1) in hearing-impaired patients under sedation, and correlation of A1 activation with hearing levels measured after cochlear implantation.

Results: In most subjects, fMRI detected significant levels of activation in the A1 region before cochlear implantation. The improvement in hearing threshold after cochlear implantation correlated strongly (linear regression coefficient, R=0.88) with the amount of activation in the A1 region detected by fMRI before cochlear implantation.

Conclusions: Functional MRI can be considered a means of assessing residual function in the A1 region in sedated hearing-impaired toddlers. With improvements in acquisition, processing, and sedation methods, fMRI may be translated into a prognostic indicator for outcome after cochlear implantation in infants.

Figure 1

General linear model z-score map showing positive (yellow) and negative (blue) activation (P<.05), overlaid on an anatomic image with the primary auditory cortex region of interest outlined in white. The patient is a 2-year-old hearing-impaired child, sedated with pentobarbital sodium (Nembutal) for scanning on a 1.5-T magnetic resonance imaging system.

Figure 2

Improvement in hearing level vs brain activation. The graph shows the strong correlation (linear regression coefficient, R=0.88) between the improvement in hearing threshold after cochlear implantation and the amount of activation in the primary auditory cortex (A1) detected by functional magnetic resonance imaging before surgery.