Structural remodeling of the brain cortex and functional recovery following hypoglossal-facial neurorrhaphy in patients with facial paralysis.

Objective: Peripheral nerve injury results in functional alterations of the corresponding active brain areas, which are closely related to functional recovery. Whether such functional plasticity induces relative anatomical structural changes remains to be investigated.

Methods: In this study, we investigated the changes in brain cortical thickness in patients with facial paralysis following neurorrhaphy treatment at different follow-up times. Using magnetic resonance imaging (MRI) and the CAT12 toolbox, voxel-based whole-brain morphometric (VBM) analysis and region of interest (ROI) of cortical thickness estimation were performed in 11 patients with left facial paralysis before and after hypoglossal-facial nerve neurorrhaphy, and the results were compared to those of 20 healthy controls. All subjects were right-handed and had a left dominant hemisphere. Based on the ROIs, correlation analysis among the cortical structural changes, the House-Brackmann (H-B) grading scale and the compound muscle action potential (cMAP) amplitudes of the facial paralyzed/reinnervated muscles in the patients was conducted.

Results: The results show dynamic changes in the thickness in the contralateral right cortex at corresponding functional areas in patients. The thickness of the ROIs was negatively correlated with the duration of facial paralysis from onset to neurorrhaphy but was positively correlated with the improvement in H-B grades and cMAP wave amplitudes recorded in the paralyzed/reinnervated facial muscles of patients. Interestingly, a significant increase in cortical thickness was observed in the ipsilateral left cortex of patients before surgery. However, the increased thickness of the left cortex was then gradually decreased and returned to the reference level of healthy controls following neurorrhaphy and reinnervation of paralyzed facial muscles.

Conclusion: We concluded that dynamic changes in both sides of the brain cortex could reflect the state and effect of functional recovery in patients from the onset of facial paralysis before treatment to reinnervation and the return of lost function following neurorrhaphy, suggesting potential observation and treatment targets to predict prognosis and further promote functional recovery.