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

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).

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.

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.

Hypermetabolic changes on FDG PET preceded signal changes on MR imaging, potentially suggesting that hypermetabolism occurred in the microscopic infiltration of lymphoma cells.