Central functional reorganization and recovery following facial-hypoglossal neurorrhaphy for facial paralysis

OBJECTIVE: Functional deficits induced by nerve injuries can be restored by achieving effective reinnervation of the denervated targets and functional reorganization of the central nervous system after nerve reconstruction. In this study, we investigated the effect and extent of cortical functional reorganization related to the ability of transferred hypoglossal neurons to restore facial function in facial paralysis patients after a surgical bridge of neurorrhaphy ectopically between the ipsilateral hypoglossal nerve and injured facial nerve. METHODS: We treated 23 patients (35.4 ± 10.3 years, 10 males) and followed them up for 2.9 ± 0.61 years. We used motor-task-related functional magnetic resonance imaging to map activation change at multiple time points before and after neurorrhaphy; 20 normal subjects were included as control. RESULTS: All patients regained facial function to some extent after neurorrhaphy. Enhanced activation in motor-related cortices gradually returned to normal levels and was positively correlated with regained facial function. The related cortical functional areas included the left middle temporal gyrus, left inferior frontal gyrus, insula, bilateral motor cortex and the supplementary motor area extending to the paracingulate involved in intensive eye closing, as well as the left superior temporal gyrus, right putamen and the bilateral motor cortex involved in lip pursing. Intriguingly, significant correlations were found between the pre-surgery activation while intensive eye closing in bilateral motor cortex and recovery of facial nerve function induced by the neurorrhaphy treatment. CONCLUSION: This is the first study mapping activation change in motor cortices at multiple time points before and after repair of the facial nerve. The cortex functional reorganization found may suggest potential treatment targets in the central nervous system for adjuvant therapies such as repetitive transcranial magnetic stimulation to further improve functional recovery.