Reorganization of central auditory pathways in vestibular schwannoma: a diffusion tensor imaging study

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Abstract
Purpose Objective information about the central auditory pathways in vestibular schwannoma can guide strategies for hearing rehabilitation and prognostication. This study aims to generate this information using diffusion tensor imaging (DTI). Methods This is a prospective observational single center study including 35 patients with vestibular schwannoma and 40 controls. Subjects underwent 64 direction multi-shell DTI which was processed to yield scalar parameters [Fractional Anisotropy (FA) and Apparent Diffusion Coefficient (ADC)] and probabilistic fiber tracking parameters. Results FA values were found to be significantly reduced at bilateral medial geniculate bodies and contralateral inferior colliculus (P < 0.001). In contrast, FA values were significantly increased at bilateral Heschl’s gyrus (P < 0.001). This was further validated by a progressive increase in FA values at bilateral Heschl’s gyri with increasing tumor size. Contralateral inferior colliculus showed a marginal increase in FA value (P = 0.006) and a marginal decrease in ADC value (P = 0.045) in patients with nonfunctional hearing as compared to patients with functional hearing. Rest of the DTI parameters were comparable across patient groups based on duration of hearing loss, hearing function, tumor location and tumor size. FA values along the tracts and the tract volumes were reduced significantly on both the sides (P < 0.001). Conclusion Vestibular schwannoma induces degenerative changes in subcortical auditory pathways bilaterally; bilateral medial geniculate bodies and contralateral inferior colliculi being the epicenters of these changes. Primary auditory cortex attempts to reorganize and adjust to the loss of these subcortical inputs.

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