Unilateral agenesis of the parotid gland with contralateral compensation hypermetabolism of FDG.

: A 75-year-old man with prostate adenocarcinoma had a baseline FDG PET/CT that demonstrated increased left parotid and absent right parotid activity. The CT revealed fat in the right parotid space and enlargement of the left parotid gland. There was no history of dry mouth. Agenesis of one or more of the salivary glands is extremely rare with only few reported cases. Awareness of anatomic variations is helpful for reviewing PET without CT or pertechnetate, sestimibi, and gallium examinations where salivary gland activity may typically be interpreted without coregistered CT.