Monitoring the biological activity of abdominal aortic aneurysms Beyond Ultrasound

Abdominal aortic aneurysms (AAAs) are an important cause of morbidity and, when ruptured, are associated with >80% mortality. Current management decisions are based on assessment of aneurysm diameter by abdominal ultrasound. However, AAA growth is non-linear and rupture can occur at small diameters or may never occur in those with large AAAs. There is a need to develop better imaging biomarkers that can identify the potential risk of rupture independent of the aneurysm diameter. Key pathobiological processes of AAA progression and rupture include neovascularisation, necrotic inflammation, microcalcification and proteolytic degradation of the extracellular matrix. These processes represent key targets for emerging imaging techniques and may confer an increased risk of expansion or rupture over and above the known patient-related risk factors. Magnetic resonance imaging, using ultrasmall superparamagnetic particles of iron oxide, can identify and track hotspots of macrophage activity. Positron emission tomography, using a variety of targeted tracers, can detect areas of inflammation, angiogenesis, hypoxia and microcalcification. By going beyond the simple monitoring of diameter expansion using ultrasound, these cellular and molecular imaging techniques may have the potential to allow improved prediction of expansion or rupture and to better guide elective surgical intervention.