Significant head motion can cause either hypermetabolic or hypometabolic cerebral activity on 18F-FDG PET/CT.

We report 2 separate cases with significant head motion causing apparent hypometabolic and hypermetabolic cerebral activity on FDG PET/CT. Case 1 is a 57-year-old man with facial numbness status post chemotherapy for mantle cell lymphoma. Restaging attenuation-corrected PET showed increased left frontal region activity, whereas nonattenuation-corrected PET demonstrated evidence of patient motion with normal physiologic left frontal cortical activity.

F-18 FDG PET-CT imaging in recurrent cerebral gliosarcoma.

We report the F-18 FDG PET-CT appearance of recurrent gliosarcoma (GS) with extracranial extension in a 47-year-old man who underwent surgical resection of a right frontal GS 5 months earlier. F-18 FDG PET demonstrated moderate uptake in the recurrent disease. GS is a very rare, biphasic primary neoplasm of the central nervous system, composed of glioblastoma multiforme mixed with a sarcomatous component.