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

Abstract

ObjectiveWe 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.MethodsWe 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).ResultsEight PIs in the six patients exhibited the rim sign with slight uptake (median SUVmax: 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.ConclusionThe 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

The Incidence of Pulmonary Embolism and Associated FDG-PET Findings in IV Contrast-Enhanced PET/CT

“…One demonstrated a complete rim of FDG avidity (Fig. 3), the previously described ''rim sign'' (27). Although only seen in a single case in our series, the rim sign may represent a relatively specific secondary sign of PE.…”

“…Multiple PET findings have been described in association with pulmonary emboli, including pulmonary artery hypermetabolism (13,(22)(23)(24), four-chamber cardiac uptake (25), and the presence of a rim of hypermetabolism surrounding a pulmonary infarction (26,27). However, the relative frequency of these findings has not been previously described.…”

Pulmonary Infarction: An Often Unrecognized Clinical Entity

“…25 Reportedly, positron emission tomography with 18 Fluorine labeled fluoro-deoxy-glucose may assist in differential diagnosis of pleural-based lung consolidations. 38 As opposed to neoplasm, pulmonary infarction features a characteristic tracer uptake along the periphery of the lesion with no uptake within the consolidation (rim sign). 38 In the opinion of the writer, however, careful history taking and radiologic imaging, be it chest X-ray or CT, go a long way toward establishing a diagnosis of pulmonary infarction.…”

“…38 As opposed to neoplasm, pulmonary infarction features a characteristic tracer uptake along the periphery of the lesion with no uptake within the consolidation (rim sign). 38 In the opinion of the writer, however, careful history taking and radiologic imaging, be it chest X-ray or CT, go a long way toward establishing a diagnosis of pulmonary infarction. The key take home messages from this review are listed in ►Table 1.…”

Acute saddle pulmonary embolism on 18F‐FDG PET/CT: diagnosis by functional imaging

“…A pulmonary infarction manifests as an area of geographical coagulative necrosis in the subpleural region with islands of viable lung parenchyma and a reparative margin of granulation tissue with a well‐defined edge consisting of palisading histiocytes and foamy macrophages . The peripheral inflammation demonstrates variable FDG uptake resulting in the “rim sign.” As pulmonary infarctions are absent in the majority of cases of PE, the absence of “rim sign” in no way reliably excludes the diagnosis . Additionally, a centrally necrotic tumour can mimic the appearance of the “rim sign” and the degree of uptake similar to low‐grade primary lung neoplasm such as adenocarcinoma.…”