Abstract
The Response Assessment in Neuro-Oncology criteria were developed as an objective tool for radiologic assessment of treatment response in high-grade gliomas. Imaging plays a critical role in the management of the patient with glioma, from initial diagnosis to posttreatment follow-up, which can be particularly challenging for radiologists. Interpreting findings after surgery, radiation, and chemotherapy requires profound knowledge about the tumor biology, as well as the peculiar changes expected to ensue as a consequence of each treatment technique. In this article, we discuss the imaging findings associated with tumor progression, tumor response, pseudoprogression, and pseudoresponse according to the Response Assessment in Neuro-Oncology criteria for high-grade and lower-grade gliomas. We describe relevant practical issues when evaluating patients with glioma, such as the need for imaging in the first 48 hours, the radiation therapy planning and isodose curves, the significance of T2/FLAIR hyperintense lesions, the impact of the timing for the evaluation after radiation therapy, and the definition of progressive disease on the histologic specimen. We also illustrate the correlation among the findings on conventional MR imaging with advanced techniques, such as perfusion, diffusion-weighted imaging, spectroscopy, and amino acid PET. Because many of the new lesions represent a mixture of tumor cells and tissue with radiation injury, the radiologist aims to identify the predominant component of the lesion and categorize the findings according to Response Assessment in Neuro-Oncology criteria so that the patient can receive the best treatment.
Highlights
The definitive diagnosis of pseudoprogression is retrospective, because it requires demonstration of decreased contrast enhancement in imaging follow-up, this pseudoprogression is conceivable if the lesion developed within the first 3–6 months after radiation therapy, if it is in the radiation field, and especially if it presents as a pattern of enhancement related to radiation-induced necrosis, ie, “Swiss cheese” or “soap bubble” enhancement (Fig 5C).[21]
Role of Advanced Imaging Techniques As we have demonstrated, an operation, radiation, and chemotherapy can lead to contrast-enhanced lesions and surrounding edema, similar to what is observed in cases of glioma progression
The evaluation of treatment response is especially challenging in neuro-oncology because an operation, radiation, and chemotherapy can lead to the development of contrast-enhanced and T2/ FLAIR hyperintense lesions that mimic glioma progression
Summary
MR imaging added fundamental information about the nonenhancing component of the tumor, depicted on T2-weighted/FLAIR sequences, and became the standard neuroimaging technique used to assess treatment response in high-grade gliomas, as updated by the same group in 2010 by publishing the RANO criteria.[10] The most substantial difference in the RANO criteria was that contrast enhancement is not the only marker of tumor viability and that it may represent posttherapy changes instead of neoplastic tissue.
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