NI-40 * MR IMAGING AND SPECTROSCOPY PROVIDES INSIGHT INTO MALIGNANT TRANSFORMATION AND IDH-MUTATION STATUS IN DIFFUSE LOW-GRADE GLIOMA

Abstract

Infiltrating low-grade gliomas (LGGs) comprise a heterogeneous class of central nervous system tumors with variable outcome. Commonly, tumors of this type recur at a higher grade upon undergoing malignant transformation (MT). The goal of this study is to further evaluate the imaging characteristics associated with MT using state-of-the-art functional magnetic resonance imaging and spectroscopy. Our study comprised 125 patients who received informed consent before undergoing surgical resection of lesions recurring from a previously diagnosed LGG. In addition to standard anatomical imaging, each patient received functional physiologic and metabolic imaging that included diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI), and long-echo metabolic spectroscopic imaging (MRSI). Tissue sample targets were chosen based on regions of suspected tumor and obtained through image-guided surgery. Each target was analyzed for histopathological markers that included IDH-mutation, relative tumor content, necrosis, CA9 status (measure of hypoxia), MIB-1 status, cellular density, SMI-31 status and vascular status. Malignant transformation was shown to have occurred in 56% of patients (44% Grade III and 12% Grade IV), while 44% of patients remained at Grade II. Significant differences were observed for lesion-level measures of choline to N-acetylasparate index (CNI), normalized apparent diffusion coefficient (nADC), and normalized Cerebral Blood Volume (nCBV) and Peak Height (PH) for patients whose lesions had undergone malignant transformation. Interestingly, measures of the ADC predicted the presence of IDH-mutations within Grade II lesions. These results are being consolidated into a multi-parametric algorithm for predicting malignant transformation, which could be of clinical interest in managing patients with recurrent LGG. Further analysis is ongoing for in vivo parameters at the region of tissue excision and correlation with histopathology