PREOPERATIVE EVALUATION OF 54 GLIOMAS BY PET WITH FLUORINE-18-FLUORODEOXYGLUCOSE AND OR CARBON-II-METHIONINE/

This study evaluates the usefulness of PET far the preoperative evalua tion of brain gliomas and methods of quantification of PET results. Me thods: Fifty-four patients with brain gliomas were studied by PET with F-18-fluorodeoxyglucose (FDG) (n = 45) and/or C-11-methianine (MET) ( n = 41) before any treatment. Results of visual analysis, calculation of glucose consumption and five tumor-to-normal brain ratios far both tracers were correlated with two histologic grading systems and with f ollow-up. Results: Visual analysis (for FDG) and tumor-to-mean cortica l uptake (T/MCU) ratio proved to be the best tools far the evaluation of PET results. Methionine was proven to be better than FDG at delinea ting low-grade gliomas. Tumor-to-mean cortical uptake ratios for FDG a nd MET were clearly correlated (r = 0.78), leading to the equation T/M CUFDG = 0.4.T/MCUMET. We showed a good correlation between FDG PET and histologic grading. MET uptake could not differentiate between low-gr ade and anaplastic astrocytomas but was significantly increased in gli oblastomas. Low-grade oligodendrogliomas exhibited high uptake of FDG and MET, probably depending more on oligodendroglial cellular differen tiation than on proliferative potential. Uptake was decreased in anapl astic oligodendrogliomas, probably due to dedifferentiation. Care must be taken with peculiar histologic subgroups, i.e., juvenile pilocytic astrocytomas and oligodendrogliomas, because of a discrepancy between high PET metabolism and low proliferative potential (good prognosis). Both tracers proved useful for the prediction of survival prognosis. Methionine proved slightly superior to FDG for predicting the histolog ic grade and prognosis of gliomas, despite the impossibility of differ entiation between Grades II and III astrocytomas with MET. This superi ority of MET could be explained by patient sampling (low number of Gra de III gliomas submitted to examination with both tracers). The combin ation of both tracers improved the overall results compared to each tr acer alone. Conclusion: Both tracers are useful for the prediction of the histologic grade and prognosis. The apparent superiority of MET ov er FDG could be due to the small number of Grade III gliomas studied w ith both tracers.