The Two Types of Right Aortic Arch

Abstract

Right aortic arch may occur as an isolated anomaly or in combination with congenital heart disease, its course under these two circumstances being generally quite different. With cyanotic heart disease, especially the tetralogy of Fallot and truncus arteriosus, the right arch is almost invariably the mirror image of the normal left arch and thus lies anterior and to the right of the trachea and the esophagus. On the other hand, when the right arch exists as an isolated anomaly, it extends posteriorly behind the esophagus. Thus, as will be shown, the presence of associated congenital heart disease and even its type are usually predictable from the location of the imprint of the right arch on the barium-filled esophagus. The two types of right aortic arch and their relationship to congenital heart disease have received little comment in the literature. Edwards (4) mentioned this correlation and Eisen (5) reported 8 patients with the posterior type of right arch, none of whom had congenital heart disease. Arkin (1) reported 6 similar cases, as did Boyle and Shaw (2). Keith et al. (11) stated that right aortic arch was rare in the presence of a normal heart and that in most of these exceptions the aorta extended behind the esophagus and descended on the left side. Neither the right aortic arch encountered in situs inversus nor the dextroposed ascending aorta are under consideration in the present discussion. Embryology For a clearer understanding of the two types of right aortic arch a brief review of the normal development of the aorta and main arteries is essential. Prior to the 30-mm. fetal stage there are a ventral aortic sac and dorsal paired aortas, connected at one time or another by six paired aortic arches (16). Certain segments of these arches disappear while other segments join to form the adult arch itself, the large arteries arising from it, the distal portion of the main pulmonary artery and its primary right and left branches, and the ductus arteriosus. Segments of the first three arches and their dorsal and ventral aortic connections form the carotid system. The ventral portion of the right fourth arch develops into the right subclavian artery and the adjacent portion of the ventral aorta becomes the innominate. The dorsal section of the right fourth arch drops out entirely. The left fourth arch persists as the adult aortic arch and left subclavian artery. The fifth arches disappear completely. The ventral portion of each sixth arch, after losing its connection to the ventral aorta, forms the extrapulmonary segment of the corresponding pulmonary artery and joins its mate to form the distal segment of the main pulmonary artery. The dorsal segment of the sixth arch on the right disappears while that on the left forms the ductus arteriosus, which becomes occluded postnatally.