Molecular Imaging of Aortic Aneurysms

Aortic aneurysms (AAs) are life-threatening permanent dilations of the aorta, frequently defined by a diameter of 1.5 times normal.1 They are subdivided anatomically into thoracic aortic aneurysms (TAAs) and abdominal aortic aneurysms (AAAs). The underlying pathogenesis differs between the 2 anatomic sites; for TAAs, the histological abnormality is medial degeneration characterized by loss of smooth muscle cells, fragmented and diminished elastic fibers, and accumulation of proteoglycans.2,3 Genetic mutations are the underlying cause of TAAs in many young or middle-aged patients.4 In contrast, the histopathology of AAAs is dominated by severe intimal atherosclerosis, chronic transmural inflammation, and remodeling of the elastic media.2,3 Analysis of gene expression demonstrated that AAAs and TAAs exhibit distinct patterns with most changes relative to normal aortas unique to each disease.3 However, several risk factors are shared between TAAs and AAAs, including smoking, hypertension, male sex, and aging.2 The age and sex dependence is illustrated by the prevalence of AAAs 2.9 to 4.9 cm in diameter, ranging from 1.3% in men aged 45 years to 54% to 12.5% at ages 75 to 84 years. For women the prevalence for the same age groups is 0% and 5.2%, respectively.5 The prevalence of TAAs also increases with age and is higher in men.6 If untreated, AAs can expand and eventually rupture, resulting in death rates as high as 90%; in 2009, mortality in the United States from AAs and dissections was >10 500.7 Both expansion rates and rupture rates of AAs increase with aneurysm size. Diagnosis of AAs generally involves anatomic imaging, typically ultrasound or CT angiography, and once diagnosed, risk stratification involves measurement of diameter by CT angiography.8 There has been controversy concerning the value of population screening for AAAs, but the Multicenter Aneurysm …