Clinical use of (11)C-methionine and (18)F-FDG-PET for germinoma in central nervous system

OBJECTIVE: The purpose of this study was to examine the (11)C-methionine (MET) and (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) findings of central nervous system (CNS) germinoma and the diagnostic utility of these findings. METHODS: We retrospectively evaluated the cases of 10 patients who were diagnosed with CNS germinoma according to their histopathological or clinical findings. All the patients underwent pretreatment MET and/or FDG-PET scans, and the resultant images were assessed qualitatively and quantitatively. In the qualitative assessments, we used 3- and 5-grade visual scoring systems for the MET- and FDG-PET images, respectively. In the quantitative assessments, the maximal standardized uptake value (SUV(max)) and the ratio of the SUV(max) of the tumor (T) divided by the mean SUV for the normal white or gray matter [T/N (WM), T/N (GM)], was calculated. RESULTS: The mean and SD values of SUV(max), T/N (WM), and T/N (GM) were 1.9 ± 1.4, 2.5 ± 1.3, and 1.7 ± 0.9 on MET-PET and 5.8 ± 2.2, 1.6 ± 0.5, and 0.8 ± 0.2 on FDG-PET, respectively. On MET-PET, only one lesion was not detected. On the other hand, on FDG-PET all of the lesions exhibited uptake values that were intermediate between those of the normal white matter and gray matter. CONCLUSION: In terms of its tumor-contouring ability, MET is a good tracer for diagnosing CNS germinomas; therefore, MET-PET is considered to be useful for planning biopsies or surgery. Although FDG-PET is capable of detecting CNS germinomas, it produced insufficient image contrast in the present study. Further studies are needed before FDG-PET can be used in clinical examinations of CNS germinoma.