Chapter 26

### INTRODUCTION

This chapter is intended to provide a clinically oriented discussion of proximal aortic disease emphasizing not only the more common problems seen in clinical practice such as ascending aneurysms and dissection but also to serve as an initial reference for many less common conditions that are generally encountered only occasionally or in specialized circumstances. A discussion of congenital aortic disease is included since an ever-increasing number of patients are now surviving into adulthood and will be encountered by vascular specialists.

### EMBRYOLOGY

The primordial heart and the vascular system appear in the middle of the third week of embryonic development. As the pharyngeal arches form during the fourth and fifth weeks of development, they are supplied by arteries—the aortic arches—that arise from the aortic sac and terminate in the dorsal aortae. Initially, the paired dorsal aortae run through the entire length of the embryo, but they soon fuse to form a single dorsal aorta, just caudal to the pharyngeal arches (Figure 26-1). When the primordial ventricle contracts, blood is pumped through the bulbus cordis and truncus arteriosus into the aortic sac, from which it is distributed to the aortic arches in the pharyngeal arches. The blood then passes into the dorsal aortae for distribution to the embryo.

###### FIGURE 26-1.

Embryonic cardiovascular system (at approximately 26 days).

Reproduced with permission from Moore K, Persaud TVN. The cardiovascular system. In: Before We Are Born. Essentials of Embryology and Birth Defects, 6th ed. Philadelphia, PA: WB Saunders; 2003:264.

During the fifth week of development, active proliferation of mesenchymal cells in the walls of the bulbus cordis results in the formation of bulbar ridges, similar ridges form in the truncus arteriosus. The bulbar and truncal ridges undergo a 180-degree spiraling. The spiral orientation of the bulbar and truncal ridges results in the formation of a spiral aorticopulmonary septum when the ridges fuse. This septum divides the bulbus cordis and truncus arteriosus into two arterial channels, the aorta and pulmonary trunk (Figure 26-2). The final transformation of the truncus arteriosus, aortic sac, aortic arches, and dorsal aorta into the adult arterial pattern are shown in Figure 26-3.1

###### FIGURE 26-2.

Partitioning of the bulbus cordis and truncus arteriosus. (A) Ventral aspect of the heart at 5 weeks. (B) Transverse sections of the truncus arteriosus and bulbus cordis, illustrating the truncal and bulbar ridges. (C) The ventral wall of the heart and truncus arteriosus have been removed to demonstrate these ridges. (D) Ventral aspect of the heart after partitioning of the truncus arteriosus. (E) Sections through the newly formed aorta (A) and pulmonary trunk (PT) show the aorticopulmonary septum. (F) Six weeks. The ventral wall of the heart and pulmonary trunk have been removed to show the aorticopulmonary septum. (G) Diagram illustrating the spiral form of ...

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