Surgery for diffuse low-grade gliomas (DLGG) functional considerations

Abstract

After many decades of controversies, guidelines now recommend -maximal surgical resection as the first therapeutic option in DLGG. This paradigmatic shift should lead neurosurgeons to switch toward an early and extensive removal of this chronic and diffuse tumoral disease of the brain. Yet, preservation of the quality of life (QoL) is also a priority in surgery for DLGG. Interestingly, because of the frequent location of DLGG within eloquent areas and due to their infiltrative feature, it was considered for a long time that the chances to perform an extensive glioma removal were low, whereas the risk to generate postoperative sequelae was high. To solve this dilemma, the brain surgeon should change his philosophy and his technique on the basis of a new concept, that is, to perform resection according to cortico-subcortical functional limits (with no margin) and not according to oncological boundaries. In other words, the neurosurgeon should see first the brain, and not the glioma, to adapt his surgical procedure to the individual cerebral anatomo-functional organization, which can be highly variable from patient to patient or even in the same patient over time due to brain reorganization induced by the slow growth of DLGG. The ultimate aim is to remove a part of the brain invaded by tumoral cells, on the condition nonetheless that it can be functionally compensated - thus, with no consequences on the QoL. In this setting, neurosurgeons need to take advantage of mapping methods to create individualized maps and management plans. These technical and conceptual advances, which consist in performing early (and possible repeated) resection(s) for DLGG, based on functional boundaries provided by pre-, intra-, and postoperative methods of mapping both at cortical and subcortical levels, in a hodotopical and plastic framework of cerebral processing, have allowed a dramatic improvement of the benefit-to-risk ratio of surgery. This chapter reviews how, in addition to functional neuroimaging, the method of intraoperative stimulation mapping, especially in awake patients, has enabled (1) an increase of the surgical indications for tumor located within eloquent areas classically considered as inoperable, (2) a significant optimization of the extent of resection, and (3) a preservation or even an improvement of the QoL. Therefore, stronger interactions between cognitive/behavioral neurosciences and oncological neurosurgery begin to solve the classical dilemma - survival versus brain functions - by giving the possibility to become more ambitious, namely, to increase both survival and QoL in DLGG patients. To this end, awake mapping should be more systematically considered, even in presumed non-eloquent areas.