Functional reorganization in the patient with progressing glioma of the pure primary motor cortex: a case report with special reference to the topographic central sulcus defined by somatosensory-evoked potential.

Abstract

The concept of human brain reorganization due to slow-growing lesions, including low-grade glioma, has been gradually and generally accepted. However, few cases have been reported in which the reorganization, especially in the topographic pure primary motor cortex, was observed during brain surgery. We report a case of slow-growing oligodendroglioma located in the pure primary motor cortex, as detected by magnetic resonance imaging that could be resected in part thanks to the brain plasticity. In addition, we describe a pitfall of topographic guidance using somatosensory-evoked potential (SEP) monitoring. A 36-year-old right-handed patient underwent resection of a gradually growing oligodendroglioma located in the right primary motor cortex, with no other adjacent lesions, 8 years after the initial biopsy. The central sulcus was defined with intraoperative SEP monitoring in both operations. Based on the findings of the intraoperative direct electrical stimulation under awake craniotomy, we suspect that motor function shifted posteriorly and reorganized beyond the central sulcus. Pure primary motor cortex could be reorganized by its own lesion. In reorganized brain, topographic central sulcus defined based on SEP findings may be an inappropriate guidance to estimate true functional area. In such a condition, intraoperative direct electrical stimulation under awake craniotomy makes it feasible to resect pure primary motor cortex invaded by tumors.