Background: Chronic inflammation is a hallmark characteristic in the patho-physiology of abdominal aortic aneurysms (AAA). In this study we sought to prospectively investigate whether inflammation was related to aortic diameter. Given that diameter has been shown to be the best predictor of AAA expansion rate, we hypothesised that larger aneurysms would have the greatest degree of inflammation.

Methods: 34 patients with AAA were imaged using fluoro-deoxyglucose positron emission tomography (FDG-PET) with CT co-registration. Uptake of FDG, which directly reflects metabolic activity and is shown to correlate with macrophage activity, was quantified as a tissue to background ratio (TBR). A TBR was calculated for the entire aorta and for the ascending, descending, abdominal and aneurysmal segments. TBR values were correlated with AAA diameter as measured on CT images. Inflammatory biomarkers, including hsCRP were also measured.

Results: The mean aneurysm diameter was 44mm (SD+/−9mm). There was no correlation between aortic diameter and TBR within the aneurymal sac (r=0.021, p=0.93). The AAA diameter also did not correlate with abdominal aortic TBR (r=0.144, p=0.54) or the total aortic TBR (r=0.058, p=0.844). There was a modest but statistically non-significant correlation between AAA diameter and hsCRP (r=0.424, p= 0.12).

Conclusions: There was no relationship between FDG uptake, a surrogate of inflammation, and AAA diameter. However, this may indicate that inflammation is a potential predictor of AAA growth rate independently of AAA diameter.

Figure 1

Image of CT, PET and co-registered image showing inflamed AAA.