NIMG-60. DIFFUSION IMAGING INTERPRETATION FOR GRADE 2 AND 3 GLIOMAS DEPENDS UPON NEW VS RECURRENT STATUS AND ENHANCING VS NON-ENHANCING STATUS

The Apparent Diffusion Coefficient (ADC) and Fractional Anisotropy (FA) are diffusion imaging parameters that are associated with degree of abnormal tissue microstructure in grade 2 and 3 gliomas. In the current study, we investigated whether the relationship between diffusion imaging and tumor histopathology score, tumor grade, and molecular characteristics is dependent on non-enhancing (NE) vs contrast-enhancing (CE) and newly-diagnosed (ND) vs recurrent (REC) disease status. We examined the median nADC and nFA values for the T2-FLAIR hyperintensity region and at the location of tissue samples in 110 ND-NE, 24 ND-CE, 60 REC-NE, and 40 REC-CE grade 2 and 3 glioma patients. We determined whether the effects of grade, histological diagnosis, and IDH and 1p19q status varied according to enhancement and recurrence status. Patients underwent a pre-surgical 3T MRI (T1-weighted IRSPGR, T2-weighted 3D FSE and/or XETA T2 FLAIR, and 6 directional axial Diffusion Weighted Imaging with b=1000s/mm2). In ND-NE patients, higher nADC and lower nFA were significantly associated with worse tumor score, higher grade, astrocytoma-like diagnosis, intact 1p19, and IDH mutation. However, in REC-NE patients, lower nADC was significantly associated with worse tumor score, intact 1p19q, and IDH wild-type. In CE patients, lower nADC and higher nFA were significantly associated with worse tumor score, and higher grade, and did not differ by recurrence status, diagnostic group or molecular characteristics. In ND-NE patients, higher nADC and lower nFA in may be driven by increased disruption of normal tissue architecture, whereas in CE patients and REC-NE patients, increased tumor cell density may drive lower nADC. These results suggest that when considering nADC and nFA values in tissue sample targeting and in evaluations of tumor severity and treatment response in grade 2 and 3 gliomas, the interpretation of these values depends upon the patient’s enhancement and newly-diagnosed vs. recurrent status.