F-18FDG positron emission tomographic image of an aortic aneurysmal thrombus

A 70-year-old woman with a history of breast cancer was referred for an F-18 fluorodeoxyglucose (FDG)-positron emission tomographic (PET) scan to evaluate a 1.1-cm single pulmonary nodule detected on a computed tomographic (CT) scan to determine whether it was benign or malignant. An incidental finding on the PET scan was an aneurysm of the descending thoracic aorta. In addition, a well-defined crescent-shaped area of absent F-18 FDG uptake was apparent in the posterior mediastinum within the expected location of the lumen of the descending thoracic aorta and along its wall. A CT scan of the chest revealed an intraluminal thrombus in the aneurysm of the descending thoracic aorta corresponding in location to the photopenic area on the F-18 FDG-PET scan. The metabolically inert area on the F-18 FDG-PET scan was thought to represent a thrombus within the aortic aneurysm.