Pulmonary FDG uptake without a CT counterpart - a pitfall in interpreting PET/CT images

Abnormal pulmonary 18F-FDG foci may occur with benign lesions like pneumonia but seldomly without any pathological CT findings. We report the case of a focal pulmonary 18F-FDG uptake without CT correlate in an initial staging examination of a patient with squamous cell carcinoma of the base of the tongue. A follow-up study did not show any suspicious lesion in this area, but pneumonia with 18F-FDG uptake in another region of the lung. 18F-FDG foci without pathological CT are a rare finding and have been associated with emboli. In the literature two main mechanisms underlying focal 18F-FDG uptake in pulmonary embolism are mentioned: an inflammatory reaction of a pre-existing vascular thrombus and an iatrogenic microembolism caused during injection. In our case the 18F-FDG accumulation was assessed as an iatrogenic pulmonary microembolism.