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INTRODUCTION

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The aorta is the largest artery in the body and connects the heart to the systemic vascular bed. It consists of both a thoracic and an abdominal portion, which are delineated by the ligamentum arteriosum. The thoracic aorta begins at the aortic valve and has four segments: the aortic root, ascending aorta, aortic arch, and descending aorta. These segments originate connections with several critical vessels including the coronary, innominate, subclavian, and carotid arteries. Similarly, the abdominal aorta, which begins as the vessel travels through the diaphragm, gives rise to the celiac, superior mesenteric, inferior mesenteric, and renal arteries and ultimately bifurcates into the common iliac arteries.

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As with other arteries, the aortic wall consists of three distinct layers. The intima, or innermost wall, primarily contains endothelial cells. These cells function as a regulatory barrier between the blood and the rest of the vessel wall and modulate processes such as thrombosis, fibrinolysis, and inflammation. The middle layer, or media, consists of vascular smooth muscle cells, elastic fibers, and other extracellular matrix components. Finally, the outer layer, or adventitia, consists primarily of collagen, nerves, and small blood vessels known as the vasa vasorum, which help provide oxygen and nutrients to the vessel wall itself. Separating each vessel layer is an additional layer of elastic lamina. Functioning in conjunction with the medial layer, these elastic fibers confer both distensibility and elastic recoil of the aortic wall, which are essential properties for normal function.

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The primary function of the aorta is transport of oxygenated blood from the left ventricle to the rest of the body. In order to accomplish this, the aorta must withstand the shear stress and transmural pressure generated by blood as it is ejected from the left ventricle. Rather than functioning as a passive conduit, the vessel wall components permit distension of the aorta during systole, thereby storing potential energy. The aorta undergoes compensatory recoil during diastole, which ensures ongoing blood flow throughout the cardiac cycle. Changes in the vessel wall, either from aging, mechanical trauma, or disease-associated pathology, may affect the elastic properties of the aorta and lead to abnormalities at any position along the vessel. According to data from the Centers for Disease Control and Prevention, diseases of the aorta were responsible for nearly 10,000 deaths in the United States in 2013. Given the significant morbidity and mortality of aortic pathology despite its relative rarity, clinicians must be able to recognize and manage the various disease processes that can affect the aorta.

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THORACIC AORTIC ANEURYSM

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An aneurysm is a pathologic, focal dilatation of a blood vessel that involves the intima, media, and adventitia. Most aneurysms affect the entire circumference of the vessel and are termed fusiforum. Saccular aneurysms involve only a small region of the vessel wall and cause diverticular outpouchings. The normal size of the thoracic aorta depends on the segment in question in addition to other ...

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