Coronal FDG-PET images of the brain (A in Clinical Presentation) demonstrate decreased metabolic activity at the right anterior temporal location (circle). T2-weighted axial and coronal MRI sections (B in Clinical Presentation) through the temporal lobes are unremarkable.

Differential Diagnosis

•  Interictal seizure focus (right temporal lobe): This is the most likely etiology for the focal hypometabolism, particularly given the history and normal MRI appearance.

•  Low-grade glioma: Low-grade tumors are usually low or non–FDG-avid and can also have this appearance on PET. Normal brain MRI makes this very unlikely, however.

•  Central nervous system infection: This can be decreased on FDG-PET but is less likely, given the history.