Metabolic and Functional Brain Mapping, Connectivity and Plasticity Applied to the Surgery of Cerebral Tumors

Although extensive surgical resection represents the first treatment in brain tumors, the risk of postoperative sequelae still persists. Consequently, neurosurgical procedure should be adapted to (1) the behavior of the tumor (2) its cerebral location (3) the individual functional organization of the brain (4) the dynamic interactions between these parameters. I first review the advantages and limitations of the non-invasive metabolic (SPECT, PET, SRM, DWI), functional (PET, fMRI, NIRS, MEG) and anatomical (DTI) neuroimaging techniques, which contribute to select the surgical indications and to plan the procedure. In addition, intraoperative electrical stimulation can be used during the resection, if necessary on awake patient when cognitive functions need to be mapped, in order to detect cortico-subcortical structures functionally essential. Second, the applications of these methods for tumor surgery are considered, with the following interests: - to understand the individual cortical functional organization before the beginning of the resection; - to improve the knowledge of the pathophysiology of brain areas frequently involved by tumor; - to map the subcortical structures all along the resection, allowing a study of the anatomo-functional connectivity; - to study the mechanisms of on-line functional reorganization, using repeated stimulations; - to perform the resection according to functional boundaries, allowing to optimize the quality of lesion removal while minimizing the risk of postoperative sequelae. Finally, the results of pre-, intra- and post-operative functional mappings can be combined, to better understand both short-term and long-term plasticity mechanisms associating functional cortical reshaping and connectivity changes - due initially to the tumor growth, then to its resection.