Evidence from cross-sectional imaging indicates abdominal but not thoracic aortic aneurysms are local manifestations of a systemic dilating diathesis

Abstract

The pathogenesis of aortic aneurysms remains unclear. There is epidemiologic and histologic evidence showing significant differences in aneurysms of the thoracic and abdominal aorta. Studies suggest that abdominal aortic aneurysms (AAA) may represent a local manifestation of a systemic dilating diathesis. It is not known whether thoracic aortic aneurysms (TAA) also have a systemic etiology. The evidence for a systemic dilating diathesis in AAA disease is reviewed and supplemented with an original morphologic study based on computed tomography (CT) comparing nonaneurysmal controls with patients with AAAs and TAAs. CT scans performed between January and November 2008 of 150 consecutive patients were examined. The morphology and dimensions of branches of the aorta in 50 TAA patients and 50 AAA patients were compared with 50 nonaneurysmal controls. Measurements of the aorta, common carotid artery (CCA), and superior mesenteric artery (SMA) were taken along with corresponding patient risk factors. Patients were well matched for age, gender, and comorbidity. Mean (SD) right CCA diameter was 9.3 +/- 1.2 in AAA patients vs 8.1 +/- 1 mm in TAA patients (P < .0001) and 7.9 +/- 0.9 mm in controls. Mean left CCA diameter was 9.3 +/- 1.2 mm in AAA patients vs 8.1+/- 0.8 mm in TAA patients (P < .0001) and 7.9 +/- 0.8 mm in controls. There was no significant difference in SMA morphology among the three groups: AAA, 8.6 +/- 1.1; TAA, 8.3 +/- .9; and controls, 8.4 +/- 0.9 mm. Multifactorial modeling accounting for risk factors, age, and gender confirmed that the diameter difference between groups retained independent statistical significance. This study provides further convincing evidence for a systemic dilating diathesis of elastic arteries in AAAs. It also highlights the differing natures of thoracic and abdominal aortic aneurysmal disease. A clear understanding of the pathophysiology of aortic aneurysms is essential. Observational studies have raised the suspicion that abdominal aortic aneurysms are a local representation of a systemic disease of the vasculature. Whether aneurysms of the thoracic aorta have a similar systemic tendency is unknown. Validation of this will open broader avenues of research clarifying understanding of the initiating factors of aneurysms and whether all aneurysms distributed through the arterial tree share the same etiology. This may in turn identify systemic treatments that eventually may allow targeted pharmaceutical management of small aortic aneurysms.