gms | German Medical Science

Objective: We aimed to investigate possible associations between cortical reorganization and clinical outcome in a group of patients with hypoglossal-facial transfer after peripheral facial palsy because of vestibular schwannoma surgery.

Methods: In our study, we examined 13 patients who had undergone hypoglossal-facial nerve transfer since 1993. Facial-hypoglossal coactivation was analyzed by EMG of the orbicularis oris muscle, neurological tests and photos of facial movements (clinical outcome). fMRI was performed with a 3 T Scanner using echo planar imaging as well as a T1-weighted anatomy 3D-dataset. Pursing the lips and elevating the tongue against the palate formed the activation phase. Postprocessing of fMRI data was performed using SPM8. Differences between the affected and the non-affected hemisphere were compared by applying a 3D-technique measuring Euklidean distances between the crossing of the interhemispheric fissure and the central sulcus and by using a 2D-flattening technique that allowed fMRI activation sites to be projected onto the surface of the brain. We measured the distance between centres of gravity of activation sites in the pre- and postcentral gyrus for the lip and the tongue representation.

Results: The more muscle activity of the orbicularis oris was detected during tongue movement against the palate, the better was the clinical outcome, as measured with the photo-documentation of the lip elevation (p < 0.005). The 2D-projection provided the following results: The cortical distance between the centres of gravity of the lip and the tongue was slightly but significantly reduced (p < 0.05) in the affected compared to the non-affected side. Most interestingly, the more coactivation of the lip during tongue movement was documented with the EMG, the less distance between the tongue and lip representation was found in the primary sensorimotor cortex (p < 0,05). In addition, the better the photographically documented final outcome of symmetry during elevation of the upper lip was, the more the tongue was represented in the direction of the lip area in the affected side (p < 0,01).

Conclusions: Our data show that a hypoglossal-facial transfer is associated with a peripheral and central coactivation of the lip and tongue area especially in those patients with a good clinical outcome. Moreover, the hypoglossal-facial transfer results in an outcome-dependent cortical reorganisation including approximation of the tongue area towards the lip area.