Functional reorganization of the corticospinal tract in a pediatric patient with an arteriovenous malformation.

Presurgical mapping in a pediatric patient diagnosed with arteriovenous malformation in the left hemisphere revealed a case of apparent functional reorganization of a white matter tract. Magnetoencephalography (MEG) was used to identify the motor fields following hand movement. As expected, motor field activity for the left hand was detected in the right hemisphere. Surprisingly, MEG activity was also detected in the right hemisphere following movement of the right hand. MEG activations served as seeds from which to launch diffusion tensor imaging tractography to delineate the corticospinal tracts (CSTs). Using the MEG activation for movement of the right hand, we delineated a tract in the right hemisphere. A tract corresponding to motor function for the left hand was also delineated in the right hemisphere. For comparison, the CSTs of the patient were launched from anatomical landmarks at the precentral gyrus, and were successfully delineated in each hemisphere. Our findings suggest that the functional delineation of white matter pathways may be more sensitive than anatomical delineation for identifying reorganization of the developing brain in response to a lesion. This study is, to our knowledge, the first description of a functional reorganization of an existing tract to serve as a CST in children.