Presurgical Functional Localization Possibilities, Limitations, and Validity

Presurgical mapping using functional neuroimaging techniques—and particularly fMRI—is now commonly used in clinical practice and not just for research applications. Presurgical functional neuroimaging 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 to lateralize and localize language and memory functions. However, particularly for cognitive brain functions, the imaging results strongly depend on the methodology and require optimal clinical standard procedures. Currently, functional neuroimaging is considered complementary to direct electrical stimulation (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 fully replace DES. In contrast, for language functions, and more recently, for memory functions, fMRI has supplanted the intracarotid amobarbital procedure (IAP) or Wada test. Diffusion tensor imaging (DTI) fiber tracking, which determines anatomical relationship between the tumor and adjacent fiber tracks, also plays a major role for presurgical mapping.