Segmental reorganization of the leg primary motor area

Abstract

Reorganization of eloquent cortex due to neighboring stressors, like tumors and epilepsy, has been previously documented. Here we report reorganization of a subregion of the primary motor cortex due to a slow-growing primary brain tumor. We report the case of a 22-year-old, right-handed male with long-standing focal partial epilepsy involving the right leg who, on imaging, had a small contrast enhancing lesion within the left leg primary motor area. He underwent resective surgery with awake motor mapping. During mapping, a specific subregion of the primary leg motor area subserving proximal leg muscles was found on a gyrus posterior to the precentral gyrus. In addition, the foot/toe area had relocated supero-medially, but remained within the pre-central gyrus. The remainder of the motor homunculus was appropriately mapped on the same gyrus. To our knowledge, this is the first report of segmental reorganization of primary motor cortex subserving an isolated muscle group. Pre-operative functional imaging does not substitute for intra-operative real-time mapping with direct electrical stimulation. This case highlights the importance of careful mapping in order to achieve gross total resection of tumors within the primary motor cortex.