The rim sign: FDG-PET/CT pattern of pulmonary infarction

OBJECTIVE We aimed to describe a pattern of rim uptake observed in lung infarction on FDG-PET/CT, called the "rim sign." It was defined as a continuous slight FDG uptake along the border of a subpleural consolidation without uptake within the consolidation. METHODS We retrospectively reviewed the FDG-PET/CT studies of 400 patients referred for thoracic oncological workup from November 2010 to July 2011. The rim sign was observed in six patients who had confirmed pulmonary infarction (PI) on MDCT showing acute pulmonary embolism (n = 4) or tumoral arterial obstruction (n = 2). RESULTS Eight PIs in the six patients exhibited the rim sign with slight uptake (median SUV(max): 3.6, 2.2-6.8) and median size of 48.5 mm (30-74). On MDCT, central lucencies, triangular shape and vessel sign were observed in 5/8, 4/8 and 1/8 cases, respectively. Two out of the eight PIs exhibited only the rim sign and none the suggestive MDCT sign. CONCLUSION The rim sign is easily recognisable at FDG-PET/CT and is strongly suggestive of PI. This pattern can be observed even in the absence of suggestive findings on MDCT. Recognition of this sign should prompt investigations for pulmonary embolism. MAIN MESSAGES • The rim sign is a slight FDG uptake around an area of subpleural consolidation • The rim sign is strongly suggestive of pulmonary infarction • Recognition of the rim sign should prompt investigations for pulmonary embolism.