Surrogates for Disease Status: Contrast Enhancement Including Limitations of Pseudoprogression and Pseudoresponse

Abstract

The disease status of gliomas with or without therapy is noninvasively assessed by clinical presentation and magnetic resonance imaging (MRI). But there is overwhelming evidence that noninvasive methods are insufficient, mainly due to the infiltrative nature and heterogeneity of glioma and, most importantly, of these tumors under/after therapy. The heterogeneity of gliomas is enhanced by any treatment, since sensitivity to tumor therapy might differ between tumor regions. Prime examples are “pseudoprogression,” which occurs under cytotoxic therapy, and “pseudoresponse,” which means the lack of contrast enhancement of tumor progression under antiangiogenic treatment. Hence, it becomes obvious that conventional MR imaging alone is not the adequate surrogate for disease status in gliomas. This chapter focuses on MR features and methods that depict tumor status. First, we describe the MR features of tumor infiltration and blood-brain barrier (BBB) damage as basic markers of disease status, then we discuss their validity as surrogates for therapy response, and we end this chapter with an exemplary, not all-comprehensive presentation of new MR methods and an outlook for the future.