Mapping the connectome in awake surgery for gliomas: an update.

The traditional principle underlying oncological neurosurgery is to remove a tumor mass displacing the brain in order to increase survival. Recently, advances in connectomics enabled an improved understanding of cerebral processing, and led to a paradigmatic shift in tumor surgery based upon interactions between neurooncology and cognitive neurosciences. First, glioma is not a focal tumor invaginated within the parenchyma but a diffuse neoplastic disease migrating in the brain. This concept resulted in a new surgical ideology, i.e., to maximally resect the invaded nervous system on the condition that eloquent neural networks are spared. Second, this led to determine what structures are crucial to preserve the quality of life (QoL) versus those that can be compensated by means of neuroplasticity. Because limitations of functional remodelling are mainly represented by the subcortical connectivity, mapping the connectome during surgery is a priority. Neurosurgeons have to switch from an image-guided surgery to a functional mapping-guided resection, namely, from a technological guidance into the operating theater to a philosophy based on the investigation of the dynamics of delocalized neural circuits throughout resection. Indeed, awake mapping with real-time monitoring of sensorimotor, visuospatial, language, executive and behavioral functions allowed an optimization of the onco-functional balance. Third, surgery should not be seen in isolation, but integrated in a global multistep therapeutic management, especially in low-grade gliomas, opening the window to repeat resections thanks to the potential of remapping over years. Such a "cognitive neurooncological surgery" which aims to improve both QoL and survival must become a "connectomal neurosurgery".