Increased 18F-fluorodeoxyglucose uptake in abdominal aortic aneurysms in positron emission/computed tomography is associated with inflammation, aortic wall instability, and acute symptoms

ObjectiveWith the established computed tomographic (CT)- morphologic parameters, only the relative, but not the individual rupture risk of abdominal aortic aneurysm (AAA), can be determined. So far, increased aortic 18F-fluorodeoxyglucose (FDG) metabolism measured by positron emission tomography (PET) has been reported in AAA with increased rupture risk. The aim of the study was to analyze the histopathologic changes in AAA wall correlated with increased FDG uptake for further implications on aortic wall stability and AAA rupture risk.MethodsFifteen patients with asymptomatic (n = 12) and symptomatic (n = 3) AAA underwent FDG-PET/CT, followed by open AAA repair. FDG-PET/CT was used for precise localization of maximum FDG uptake, and the maximum standard uptake values (SUVmax) were calculated. Biopsies of the AAA wall were operatively collected from areas with maximum FDG uptake, immunohistologically stained, and semiquantitatively analyzed for inflammatory infiltrates, vascular smooth muscle cells (VSMC), matrix metalloproteinase (MMP)-2 and -9 expression, as well as for elastin and collagenous fibers.ResultsSymptomatic AAA showed significantly increased FDG uptake compared with asymptomatic AAA (SUVmax, 3.5 ± 0.6 vs 7.5 ± 3; P < .001). Thus, increased FDG uptake was correlated with higher densities of inflammatory infiltrates (r = +0.87, P < .01) and macrophage and T-cell infiltrations (r = +0.95, P < .01 and r = +0.66, P < .05), with higher MMP-9 expressions (r = +0.86; P < .01), and with reduction of collagen fiber (r = –0.76; P < .01) and VSMCs (r = –0.71; P < .01). Consecutive correlations were found for total inflammatory infiltrates, T lymphocytes, and macrophages with MMP-9 expression (r = +0.79, +0.79 and +0.74; P < .01). Moreover, MMP-9 expression was correlated with decreasing collagen fiber content (r = –0.53, P < .05) and VSMC density (r = –0.57, P < .05).ConclusionsMaximum aortic FDG uptake correlated significantly with inflammation, followed by increased MMP expression and histopathologic characteristics of aneurysm wall instability and clinical symptoms. Therefore, FDG-PET/CT might be a new diagnostic technique to study AAA disease in vivo and may contribute to improve prediction of individual AAA rupture risk.

Clinical RelevanceWith the established CT morphologic parameters, the exact rupture risk of individual abdominal aortic aneurysm (AAA) cannot be determined. Regarding AAA formation and rupture, metabolic processes that weaken the aortic wall, such as chronic inflammation and proteolysis, have a pivotal role. This pilot study demonstrated that increased metabolism in the AAA wall can be visualized by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT). Furthermore, aortic FDG uptake correlated with inflammation, histopathologic characteristics of aneurysm wall instability, and clinical symptoms. Therefore, after further investigation FDG-PET/CT might be a new diagnostic technique to assess AAA wall stability in vivo and consequently may contribute to improved prediction of individual AAA rupture risk.