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CHAPTER SUMMARY AND CENTRAL ILLUSTRATION

Chapter Summary

This chapter discusses the pathophysiology, diagnosis, and management of diseases of the aorta, including both aortic aneurysm and dissection, from the aortic valve to aortic bifurcation. Aneurysmal disease differs between the ascending portion and the descending and thoracoabdominal segments (see Fuster and Hurst’s Central Illustration). Genetically mediated degeneration of the aortic wall results in disruption of the normally uniform pattern of regularly spaced aortic lamellae, leading to fluid-filled lacunae and decreased aortic strength. Aneurysmal dilatation ensues. Monitoring by echocardiography, computed tomography (CT), or magnetic resonance imaging (MRI) is recommended. Surgical repair is recommended in patients with symptomatic or rapidly expanding aneurysms or at aortic diameters >5.5 cm. Thresholds for intervention are lower in patients with certain genetic conditions/syndromes. Whole exome sequencing is recommended for affected individuals, and first-order relatives should undergo screening for thoracic aortic aneurysms. Adult male smokers and former smokers should undergo screening for abdominal aortic aneurysm. Aortic dissection occurs catastrophically without premonitory symptoms, often precipitated by conditions that raise blood pressure and hemodynamic stress acting on an enlarged aorta. Urgent surgery is required for ascending (Type A) aortic dissections. Descending (Type B) dissections can usually be managed medically. Endovascular approaches are increasingly employed as alternatives to open surgical repair, but they carry a risk of endoleak, requiring postprocedural imaging surveillance.

eFig 23-01 Chapter 23: Diseases of the Aorta

BIOLOGY OF THE AORTA

The biological and mechanical properties of the normal aorta involve intrinsic contraction and relaxation that enhance hemodynamics through interaction with left ventricular (LV) ejection. Normally the largest elastic artery, the trilaminar aortic wall consists of a tunica intima, tunica media, and tunica adventitia (Fig. 23–1). The innermost lining of the tunica intima is the endothelium, resting on a thin basal lamina. The subendothelial tissue is comprised of fibroblasts, collagen fibers, elastic fibers, and mucoid ground substance. An internal elastic membrane forms the outer lining of the tunica intima. The tunica media is approximately 1 mm thick, comprised of elastin, smooth muscle cells, collagen, and ground substance. The predominance of elastic fibers in the aortic wall and their arrangement as circumferential lamellae distinguish it from the smaller muscular arteries. A lamellar unit is made up of two concentric elastic lamellae containing smooth muscle cells, collagen, and ground substance. The thoracic aorta incorporates 35 to 56 lamellar units and the abdominal aorta about 28 units. Surrounding the tunica media is the tunica adventitia, which is composed of loose connective tissue, including fibroblasts, relatively small amounts of collagen fibers, elastin, and ground substance. The adventitia strengthens the aorta and is essential to aortic surgeons for secure suturing of tissues. Within the tunica adventitia lie the nervi vasorum and vasa vasorum. The arteries arising along the course of the aorta give rise to the vasa vasorum, which develop into a capillary ...

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