10022-NI-1 Evaluation of FDG PET Uptake Reduction in Non-contrast-enhanced Gliomas

Abstract Purpose 18F-fluorodeoxyglucose positron emission tomography (FDG PET) reflects glucose metabolism and accumulates in highly malignant tumors. In low-grade gliomas, uptake is lower than in surrounding normal brain cells with high uptake, resulting in clear contrast. This study focuses on the decreased FDG uptake in non-contrast-enhanced gliomas to clarify the characteristics of each histological type. Methods We analyzed 118 patients who underwent FDG PET between 2012 and 2022: 27 with glioblastoma, IDH-wildtype (G), 55 with astrocytoma, IDH-mutant (A), and 36 with oligodendroglioma, IDH-mutant and 1p/19q codeleted (O). Z-scores were calculated compared to a normal brain database, and the extent and degree of decreased uptake in tumor regions were evaluated. Results Mean age was 42.4±13 years, with 61 males. The volume of regions with Z-score≤-2 (mm3) averaged 58.5±56.2 (G: 54.5±65, A: 68.3±60.5, O: 46.5±37.9), extending significantly beyond the T2 hyperintense volume (mm3), which averaged 34.2±30.9 (G: 27.9±27.4, A: 40.9±37, O: 28.7±20.1) (p < 0.001). Mean Z-score was -4. 4±1.3 (G: -3. 5±0. 8, A: -5. 0±1.4, O: -4.1±1), with A significantly lower and G significantly higher (p < 0.001). Z2 (proportion of -2≥Z score>-3 region within Z score≤-2 region) and Z3 showed A<O<G, with G being the most extensive. The difference disappeared in Z4 and Z5, and from Z6 to Z9, A>O>G, with A being the most extensive. T2 hyperintense region and mean Z-score showed significant negative correlations in group A (r=-0.6, p < 0.001) and group O (r=-0. 44, p = 0.007), but not in group G. Discussion Non-contrast-enhanced gliomas were visualized as areas of decreased uptake on FDG PET. These areas extended beyond the T2 hyperintense regions, with group A showing severe decreased uptake and group G showing relatively mild decreased uptake. In group G, FDG uptake did not decrease even when T2 hyperintense regions increased. The reduction in FDG uptake may reflect tumor characteristics such as tumor compression and infiltration of normal brain tissue.