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Ascending thoracic aortic aneurysm (ATAA) is defined as a dilatation of the ascending aorta producing a cross sectional diameter more than 1.5 times its normal value; values between 1.1 and 1.5 are considered dilated or ectatic ascending aorta. Normal values have been established by different imaging techniques: echocardiography, computed tomography (CT) and magnetic resonance imaging (MRI)1–3 (table 1). Aneurysmal disease of the aorta is clinically important since, as the diameter of the aorta expands, linear wall stress increases, which in turn directly increases the risk of spontaneous aortic rupture—an event with extremely poor prognosis for the patient. Thoracic aortic aneurysms (TAAs) involve the ascending aorta most commonly (50%), followed by the descending aorta (40%), whereas arch aneurysms (10%) and thoraco-abdominal aneurysms (10%) occur less often. In 25% of patients with ATAA, concomitant abdominal aortic aneurysm is present. Anatomical distinction is important since the aetiology, natural history and treatment differ for each of these segments.
The incidence of thoracic aneurysms has been classically estimated to be 2–5 cases per 100 000/year; however, in recent series this figure has been reported to reach 10.4 cases per 100 000/year.4 This increase is probably due to improvements in diagnosis and case ascertainment. There are several significant differences between TAA and abdominal aneurysms. Age at onset for TAA is 10 years earlier than for abdominal aneurysms (65 vs 75 years); abdominal aneurysms are more predominant in men, with a 6:1 male-to-female ratio, whereas TAAs occur only slightly more frequently in men (1.7:1).
The ascending aorta has a greater concentration of elastic fibres and is more compliant than the descending aorta. The elastin-to-collagen ratio progressively decreases as the aorta traverses distally into the descending thoracic and abdominal aorta. The difference in anatomical and …
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