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Background The molecular diagnosis of gliomas such as isocitrate dehydrogenase (IDH) status (wild-type [wt] or mutation [mut]) is especially important in the 2016 World Health Organization (WHO) classification. Positron emission tomography (PET) has afforded molecular and metabolic diagnostic imaging. The present study aimed to define the interrelationship between the 2016 WHO classification of gliomas and the integrated data from PET images using multiple tracers, including 18F-fluorodeoxyglucose (18F-FDG), 11C-methionine (11C-MET), 18F-fluorothymidine (18F-FLT), and 18F-fluoromisonidazole (18F-FMISO). Methods This retrospective, single-center study comprised 113 patients with newly diagnosed glioma based on the 2016 WHO criteria. Patients were divided into 4 glioma subtypes (Mut, Codel, Wt, and glioblastoma multiforme [GBM]). Tumor standardized uptake value (SUV) divided by mean normal cortical SUV (tumor–normal tissue ratio [TNR]) was calculated for 18F-FDG, 11C-MET, and 18F-FLT. Tumor–blood SUV ratio (TBR) was calculated for 18F-FMISO. To assess the diagnostic accuracy of PET tracers in distinguishing glioma subtypes, a comparative analysis of TNRs and TBR as well as the metabolic tumor volume (MTV) were calculated by Scheffe's multiple comparison procedure for each PET tracer following the Kruskal–Wallis test. Results The differences in mean 18F-FLT TNR and 18F-FMISO TBR were significant between GBM and other glioma subtypes (P < .001). Regarding the comparison between Gd-T1WI volumes and 18F-FLT MTVs or 18F-FMISO MTVs, we identified significant differences between Wt and Mut or Codel (P < .01). Conclusion Combined administration of 4 PET tracers might aid in the preoperative differential diagnosis of gliomas according to the 2016 WHO criteria.

OBJECT: Neuroendocrine carcinoma (NEC) is a malignant tumor that usually arises in the lung, pancreas and gastrointestinal tract. Brain metastasis of NEC is merely reported. Herein, we report two cases of NEC in the brain mimicking glioblastoma (GBM). CASES: Both patients were in their 60s, cystic lesions with peritumoral edema affected the temporal lobe. Cyst walls were thin but hyperintense in diffusion weighted images implying increased cellularity. Positron emission tomography (PET) revealed malignant nature by strong uptake of methionine (MET), fluorothymidine (FLT) and fluoromisonidazole likewise GBM. However, fluorodeoxyglucose (FDG) indicated relatively weak uptakes compared as GBM. Both tumors were resected under the preoperative diagnosis of GBM, however, pathological diagnoses were NEC by immunohistochemical finding of negative GFAP and positive markers of neuroendocrine differentiation. Systemic examination failed to reveal the origin. Both cases underwent radiotherapy. One case was lost by spinal dissemination 11 months after the operation. DISCUSSION: FDG-PET of neuroendocrine tumor in the extracranial lesion does not always demonstrate strong uptake. FDG-PET for NEC in the brain could be less accumulated than GBM, while it should be evaluated keeping in mind that the background level of FDG would be high in the brain tissue. In case of malignant tumors endorsed by other tracer such as MET and FLT, inconsistent FDG-PET finding might be useful for the diagnosis of NEC in the brain.