False-Positive 18F-FDG and 18F-Fluorothymidine Uptake in a Patient With Round Atelectasis.

A 64-year-old man with no significant medical history demonstrated a right lower lobe opacity on routine chest radiography. Transaxial CT showed a round, well-circumscribed, pleural mass with comet-tail sign in the right lower lobe and pleural thickening with pleural effusion. F-FDG PET/CT showed hypermetabolic activity in the mass (SUVmax 9.61). F-fluorothymidine PET/CT also showed mild increased uptake in the mass (SUVmax 3.26). Lung biopsy and follow-up CT scan revealed round atelectasis.