Quantitative and Visual Characteristics of Primary Central Nervous System Lymphoma on ¹⁸F-FDG-PET

Primary central nervous system lymphomas (PCNSLs) are rare progressive brain tumors, whose managements are significantly different from other solid tumors, especially glioblastomas. Therefore, an early diagnosis is of great significance. ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET), which can measure the glucose metabolic rate in the brain, is an increasingly common tool for early diagnosis. Twenty-five immunocompetent patients with PCNSL were reviewed in this study to describe the general characteristics of PCNSL patients' ¹⁸F-FDG-PET scans. Quantitative features included a radically enhanced maximum standardized uptake value (SUV_max) with a mean value of 23.8 ± 7.9 and a 5.8 ± 1.8 mean ratio of tumor-to-normal contralateral cortex activity (T/N). Visual characteristics, such as favored locations in the brain, lesion numbers, tumor shape, metabolic inhibition, and structural shift were determined as well. PCNSL was found to favor the cortex, especially the frontal lobe, followed by the basal ganglia and corpus callosum. All PCNSLs were near the lateral ventricular area. Tumor shapes were subdivided into three groups: diffuse, round, and irregular patterns. Reduced radiation was observed in the ipsilateral cortex, the basal ganglia and the contralateral cerebellum. The lateral ventricles were prone to be compressed on the side ipsilateral to the tumor, pushing the midline towards the contralateral side of the brain. In conclusion, aside from SUV_max and T/N values, other visual characteristics are also available to facilitate the differentiation of PCNSLs from other brain conditions on ¹⁸F-FDG-PET scans.