Presurgical functional localization possibilities, limitations, and validity

Over the last two decades, presurgical mapping using functional neuroimaging techniques – and particularly fMRI – has made considerable progress. FMRI is now commonly used in the clinical practice and not just for research applications. Presurgical functional neuroim-aging with its contributions to surgical planning and to the prediction of postoperative outcome is now well established. Validation studies of functional imaging techniques have shown the potential of fMRI to localize motor areas and also to lateralize and localize language and, more recently, memory functions. However, particularly for cognitive brain functions, the imaging results strongly depend on the methodology requiring optimal clinical standard procedures. Currently, functional neuroimaging is considered as complementary to direct electrical stimulations (DES) providing additional information, such as information on the entire functional network and on the contralateral hemisphere, which is not accessible to DES. Until now, fMRI cannot replace DES. In contrast, for language functions, fMRI has largely replaced the intracarotid amobarbital procedure (IAP), which could be the case also for memory functions in the near future. Diffusion tensor imaging (DTI) fiber tracking is a more recent, but already in some centers, well-established technique, and its value in presurgical mapping requires further work.