Task-based presurgical functional mri in patients with brain tumors

Abstract

Neurosurgery in functionally important brain areas carries a high risk for postoperative neurological deficits. In patients with brain tumors, functional magnetic resonance imaging (fMRI) facilitates presurgical planning and evaluation of surgical outcome for the estimation of an as good as possible balance between maximal tumor resection and minimal loss of function. To this end fMRI is also applied intraoperatively for functional neuronaviga-tion preferably in combination with DTI-tractography. However, fMRI has not reached the status of a standard diagnostic neuroimaging procedure, yet. Preoperative task-based fMRI represents the best established and validated clinical application of fMRI, is increasingly performed in larger medical neurocenters, and in this context can only be performed exclusively in individual patients. Therefore, it differs fundamentally from research application in neuroscience. This chapter provides a review of the current literature and presents optimized task-based presurgical fMRI protocols for motor, somatosensory, and language function, along with a standardized data evaluation protocol using a dynamic statistical threshold. Examples of physiological brain activation are given, criteria for the selection of candidates for presurgical fMRI are provided, and illustrative cases with typical and atypical presurgical fMRI findings are presented. Complementary applications with diffusion tensor imaging (DTI) and DTI-tractography (DTT) are highlighted. Finally, important diagnostic capabilities and limitations of presurgical fMRI are discussed. In conclusion, fMRI is feasible for advanced multi-modal MR-neuroimaging in the clinical setting and provides important diagnostic information noninvasively, which is otherwise unavailable. Task-based preoperative fMRI is valid, reasonably sensitive, and accurate to localize the different representations of the human body in the primary motor and somatosensory cortex prior to brain tumor surgery, which in general also applies to language localization and lateralization. Although there is a substantial body of studies on presurgical language fMRI available, the results are still heterogeneous. Here, fMRI has at least the potential to help to reduce the number of invasive diagnostic measures needed and to guide their targeted application. If, and to what extent, intraoperative electrocorticography (ECoG) or the Wada test can be replaced is still not clear, yet. The integration of fMRI with DTI and DTT is complementary and increasingly used, providing important pretherapeutic and intraoperative information on essential cortical and subcortical functional structures in relation to the surgical target.