Hearing Thresholds and fMRI of Auditory Cortex Following Eighth Cranial Nerve Surgery

Abstract

Objective

Determine whether auditory cortex (AC) organization changed following eighth cranial nerve surgery in adults with vestibular-cochlear nerve pathologies. We examined whether hearing thresholds before and after surgery correlated with increased ipsilateral activation of AC from the intact ear.

Study Design

During magnetic resonance imaging sessions before and 3 and 6 months after surgery, subjects listened with the intact ear to noise-like random spectrogram sounds.

Setting

Departments of Radiology and Otolaryngology of Washington University School of Medicine.

Subjects and Methods

Three patients with acoustic neuromas received Gamma Knife radiosurgery (GK); 1 patient with Meniere’s disease and 5 with acoustic neuromas had surgical resections (SR); 2 of the latter also had GK. Hearing thresholds in each ear were for pure tone stimuli from 250 to 8000 Hz before and after surgery (3 and 6 months). At the same intervals, we imaged blood oxygen level–dependent responses to auditory stimulation of the intact ear using an interrupted single-event design.

Results

Hearing thresholds in 2 of 3 individuals treated with GK did not change. Five of 6 individuals became unilaterally deaf after SRs. Ipsilateral AC activity was present before surgery in 6 of 9 individuals with ipsilateral spatial extents greater than contralateral in 3 of 9. Greater contralateral predominance was significant especially in left compared to right ear affected individuals, including those treated by GK.

Conclusion

Lateralization of auditory-evoked responses in AC did not change significantly after surgery possibly due to preexisting sensory loss before surgery, indicating that less than profound loss may prompt cortical reorganization.