Hypermetabolic change as a possible predictive sign of a relapsed central nervous system lymphoma

PURPOSE: A patient with abdominal lymphoma who had been in complete remission for 6 years presented with a 1-month history of dysarthria. The aim of our report is to discuss the discordance of the patient's results between magnetic resonance (MR) imaging and F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET). MATERIALS AND METHODS: After the onset, FDG PET and brain MR imaging were performed. The FDG PET study included whole-body and brain scan. The MR study included pre- and postcontrast T1, T2, fluid-attenuated inversion recovery and diffusion-weighted sequences. RESULTS: Brain MR imaging showed a localized abnormal signal around the left Sylvian fissure in any sequence, although a postcontrast study exhibited poor enhancement in the lesion. Brain PET showed a widespread area of slightly increased uptake in the brain on the left side, which was quite inconsistent with the MR results. After 4 months, follow-up MR imaging revealed a widespread abnormal signal, with enhancing masses, in the hypermetabolic region. CONCLUSIONS: Hypermetabolic changes on FDG PET preceded signal changes on MR imaging, potentially suggesting that hypermetabolism occurred in the microscopic infiltration of lymphoma cells.