Dual-phase F-18 FDG PET cannot increase the diagnostic accuracy to differentiate solitary pulmonary nodules

Distinguishing malignant from benign solitary pulmonary nodules (SPN) is a challenge because both can show increased FDG uptake. Traditionally, a standardized uptake value (SUV) of 2.5 to 3.8 on a routine FDG-positron emission tomography (PET) image has been proposed as the optimal threshold for separating malignant from benign SPN. However, there is still considerable overlap between SUV of malignant and benign SPN. Recently, dual-phase FDG-PET with a higher sensitivity and specificity for the detection of SPN has been reported. Increased SUV in the SPN was considered as malignant, but decreased SUV in the SPN was considered as benign. We present 2 cases with misdiagnosed results that serves as a reminder that to make a final interpretation of SPN by a change of SUV on dual-phase FDG-PET, one must be very careful.