Molecular Imaging Predicts Risk for Abdominal Aortic Aneurysms

Several newly identified markers could provide valuable insight to predict the risk of rupture abdominal aortic aneurysms (AAA), according to new research out of Europe.

The study’s findings were published in the October 2013 issue of the Journal of Nuclear Medicine. Positron emission tomography/computed tomography (PET/CT) imaging sans revealed that dense white blood cells in the outermost connective tissue in the vascular wall, increased C-reactive protein and a loss of smooth muscle cells in the middle layer of the vascular wall are all factors that may indicate future AAA rupture.

An abdominal aneurysm causes stress on the wall of the aorta, which can rupture it. Rupture of AAA is the 13th leading cause of death in western society and leads to substantial morbidity and mortality in the aging population. AAA is typically asymptomatic; therefore, it is an effective prediction of a rupture is crucial.

To determine potential markers that could be predictive of AAA rupture, researchers conducted ¹⁸F-FDG PET/CT scans on 18 patients with AAA diagnosed by ultrasound. Ten of the patients had no uptake of the ¹⁸F-FDG, while eight had positive uptake of the imaging agent. Biopsy specimens were then retrieved from each of the patients; patients with positive ¹⁸F-FDG uptake had tissue taken from both the site of the positive uptake and a distant negative site of the aortic wall.

“Our approach allows us—for the first time to our knowledge—to analyze spots of high ¹⁸F-FDG uptake and compare them to a distant inactive zone of the same aneurysm. We further compared these biopsies to fragments collected in patients with negative ¹⁸F-FDG uptake. This strategy allowed for the discrimination of biologic alterations associated with ¹⁸F-FDG uptake that would help identify relevant biologic markers predictive of rupture,” said Audrey Courtois, PhD, from the laboratory of connective tissues biology, GIGA-R, University of Liège (Belgium), and lead author of the study.

The tissue from the area of positive ¹⁸F-FDG uptake were characterized by an increased number of inflammatory cells in the outermost connective tissue, a high level of C-reactive protein and an extreme decrease in smooth muscle cells, as compared to the biopsies from areas of no uptake. Furthermore, an increase in several matrix metalloproteinase enzymes was seen in the tissue with positive ¹⁸F-FDG uptake.

“These data suggest that a PET scan with positive ¹⁸F-FDG uptake provide diagnostic support to proceed without delay to aneurysm surgery, despite a person’s age or operative risk. However, the absence of FDG uptake at the level of the aneurismal aortic wall can help us make a safe decision to avoid unnecessary surgery and decrease the burden of healthcare costs,” concluded Dr. Courtois. “This ¹⁸F-FDG PET/CT study, with an arterial phase CT, allows us to fully characterize the disease, including the conventional risk factors such as the size of the aneurysm. Although much of the current research is being conducted in the field of oncology, the current study further strengthens ¹⁸F-FDG PET/CT as a decisive tool in the management of inflammatory disorders.”

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