18F-FET PET Pitfall in Pituitary Imaging: False-positive Uptake Due to Neurosarcoidosis

We report a rare pituitary imaging pitfall on ¹⁸ F-FET PET/CT in a 38-year-old man with a history of treated pulmonary sarcoidosis. MRIs demonstrated a left-sided pituitary neuroendocrine tumor (PitNET)/pituitary adenoma. ¹⁸ F-FET PET/CT showed discordant bilateral uptake with higher activity on the right side. Histopathological analysis demonstrated a PitNET of corticotroph type on the left side and noncaseating granulomas consistent with sarcoidosis on the right side. Neurosarcoidosis should be considered a potential cause of false-positive ¹⁸ F-FET uptake.