Introduction: The presence of functional areas close or inside gliomas prevents the complete resection of these tumors. It has been recently demonstrated that slow tumor invasion promotes topographic plasticity allowing staged resection of those tumors (1). We aimed to produce a “virtual lesion” in eloquent areas located near or within tumors either using repetitive transcranial magnetic stimulation (rTMS) or continuous high-frequency cortical electrical stimulation (HFCS), in order to promote plasticity and increase the extent of tumor resection.

Methods: In 3 cases of gliomas invading Broca’s area (1 astrocytoma, 1 oligodendroglioma, 1 anaplastic astrocytoma), previously partially removed using awake cortical monitoring, we either stimulated with daily rTMS, or through an implanted subdural grid using continuous HFCS, over the eloquent cortex located within the tumor remnant. The stimulus intensity was set daily to the threshold of mild speech disturbance without any other neurological effects.

Results: While rTMS produced a reinforcement of fluent speech tasks, but not topographic plasticity, HFCS achieved the displacement of speech functions, and a more radical resection of the tumor was possible in a repeated surgery. Reorganization of motor language areas was demonstrated both with functional magnetic resonance and cortical stimulation. Motor language areas were identified at the right hemisphere where previously they were absent, or at different places at the left hemisphere than previously found. The patients’ speech fluency improved after stimulation.

Conclusions: We provide evidence of induced topographic plasticity using HFCS in eloquent areas within a tumor, allowing an increased tumor removal. These results may have important implications for the future of brain tumor surgery, rehabilitation and reparative neuroscience.

Patient Care: It will allow to increase the extent of resection of brain tumors located at or near eloquent cortical areas

Learning Objectives: Learning objectives: By the conclusion of this session, participants should be able to 1) Understand the problem of surgical resection of tumors including or close to eloquent areas, 2) Describe the possibility of cortical plasticity and its induction by low grade gliomas, 3) Identify a possible strategy to induce cortical plasticity and thus increase the extent of tumor removal.

References: 1. Robles SG, Gatignol P, Lehéricy S, Duffau H. Long-term brain plasticity allowing a multistage surgical approach to World Health Organization Grade II gliomas in eloquent areas. J Neurosurg. 2008 Oct;109(4):615-24.