Low-Grade Gliomas: Intraoperative Electrical Stimulations

Abstract

The goal of low-grade gliomas (LGG) surgery is to optimize the extent of resection, while minimizing the risk of permanent neurological deficit. Because LGG often invade “eloquent areas” and because of major interindividual anatomofunctional variability, the cortical functional organization, the subcortical connectivity and the brain plastic potential should be studied at the individual scale. Indeed, cortical and subcortical structures essential for brain functions must be detected and preserved. Presurgical functional neuroimaging and tractography can show the relationships between eloquent regions and the tumor, but they have several methodological limitations. Consequently, intraoperative electro-stimulation mapping (IES) is more and more used by neurosurgeons, to tailor the resection according to individual functional boundaries. IES can be performed under general anesthesia for motor mapping, or on awake patient for somatosensory (and even motor), visuo-spatial, language and cognitive mapping. This is an easy, accurate, reliable and safe technique of detection of cortical areas, white matter pathways and deep gray nuclei crucial for the function. Thus, IES enables: (i) to study the individual cortical functional organization before any resection; (ii) to understand the pathophysiology of cerebral “eloquent” areas; (iii) to map the subcortical structures throughout the resection, allowing a study of the anatomo-functional connectivity; (iv) to analyze the mechanisms of on-line short-term plasticity, using repeated IES; (v) to tailor the resection according to individual cortico-subcortical functional boundaries. Moreover, IES can be combined with repeated pre-and post-operative functional neuroimaging, before and after surgery, both to validate these non-invasive techniques and to study the reorganization of the functional maps over time at the individual scale. Such plastic potential can open the door to multiple surgeries spaced by several months or years, with the goal to optimize the benefit/risk ratio of surgery for LGG, i.e. to increase the extent of resection while preserving and even improving the quality of life. IES also represents a unique tool to improve our knowledge of brain processing and to revisit the classical model of cognitive neurosciences, by switching from a localisationnist to a “hodotopic” view of cerebral organization.