A 68-year-old woman with colon carcinoma was referred to F-FDG PET/CT imaging for staging. In addition to primary tumor involvement, PET/CT demonstrated focal FDG uptake in the right temporal lobe suggestive of primary brain tumor or metastasis. To delineate the lesion, a brain MRI scan showed sigmoid sinus thrombosis and vasogenic edema in the right temporal lobe. The patient presented a history of right-sided headache that began 1 week before the PET/CT. Neurological examination and MRI findings were concluded as subacute venous infarct due to sigmoid sinus thrombosis and that is a potential cause for false-positive FDG uptake on PET/CT.