Teaching Case

A widespread variety of the aortic arch and the origin of its branches has been frequently reported in the literature to date. However, symptoms or disability related to congenital anomalies of cardiovascular pattern are not always seen, unless they are associated with a congenital cardiac disease. Thus, some of the clinical cases in the literature with a right-sided aortic arch were incidental findings and neither dysphagia nor dyspnea was referred; some of them were found at autopsy or during diagnostic procedures in patients who died from unrelated causes. We report a case of the right-sided aortic arch with a retroesophageal bulge and an aberrant left subclavian artery. The embryological hypotheses for these anomalies are discussed, keeping in mind that correct identification of such variations may be useful to physicians and surgeons in order to avoid major surgical complications.

A 79-year-old man came to our attention during a routine X-ray examination of the chest, which detected the presence of the right aortic knob (Fig. 1). Subsequently, the patient underwent a CT scan for more detailed information. The CT showed a right-sided aortic arch (Fig. 2a and b) with an aberrant left subclavian artery arising from the first segment of the dorsal aorta and running behind the esophagus. The brachiocephalic trunk and the left common carotid artery were normally placed. The aorta arose normally from the left ventricle and was in relationship with the pulmonary trunk. The ascending aorta was in its usual position but the arch was right-sided. The descending aorta was in the midline. The aortic branches arose from the right to the left as follows: the brachiocephalic trunk (that gives rise to the right subclavian artery and the right common carotid artery) and the left common carotid artery were normally placed; the left subclavian artery was in aberrant retroesophageal position. The pulmonary and cardiac patterns did not show any anomalies. No lesions were found in the abdominal internal organs. The patient did not complain of symptoms such as dysphagia or dyspnea.

As reported by Bialowas et al. (1) apart from cases of complete "situs viscerum inversus", the following anatomical changes can be distinguished: (1) a left-sided aortic arch with a properly established system of branches; (2) a left-sided aortic arch with an aberrant right subclavian artery; (3) a left-sided aortic arch with a retroesophageal course and a right-sided descending aorta or retroesophageal course of the brachiocephalic trunk onto the right side; (4) a right-sided aortic arch of the "symmetric" type usually coexisting with cyanotic congenital heart lesions; (5) a right-sided aortic arch with a retroesophageal bulge and an aberrant left subclavian artery (as in our case); and (6) a right-sided aortic arch with an aorta descending on the left side or a brachiocephalic trunk lying behind the esophagus on the left side. The anatomical variations of the aortic arch and its branches may be explained by embryological development, as suggested by Edwards' hypothesis (2). Normally, the aortic arch is derived from the left fourth embryonic arch and the right fourth arch: after giving rise to the right common carotid artery, it continues into the right subclavian artery. The distal end of the left sixth arch connects the left pulmonary artery to the left extremity of the aortic arch as the arterial duct or ligament. The same connection between the aorta and the pulmonary artery is on the right side. Four branches arise from the aortic arch as follows: the right common carotid artery, the right subclavian artery, the left subclavian artery and the left common carotid artery. When the fusion of the embryonic arches is complete, there are three vessels arising from the right side to the left side: the brachiocephalic trunk, the left common carotid artery and the left subclavian artery. The regression of different segment within the embryologic aortic pattern give rise to the final setting of the aorta, its arch and branches. Normally, the regression of the right cephalic arch occurs after that of the right subclavian artery and leads to the formation of the normal aortic system. On the other hand, an interruption at different levels explains the persistence of a right fourth aortic arch, as studied by different authors (3). We agree with other authors that there are three types of anomalies. In the first one, the regression occurs between the left common carotid artery and the left subclavian artery with the resultant aberrant left subclavian artery. In this type, the left subclavian artery arises from the dorsal, right-sided aortic arch and goes to the left arm, running behind the esophagus. The descending aorta is generally left-sided to the midline. Thus, the vascular ring is formed around the trachea and esophagus, by the right arch on the right side, the left subclavian artery posteriorly, the ligamentum arteriosum on the left and the pulmonary arterial bifurcation anteriorly. The second type is the right aortic arch with mirror-image branching of the arch vessels. The interruption is between the descending aorta, right-sided, and the left subclavian artery. The branches arise from the aortic arch as follows: firstly the left brachiocephalic trunk, passing over the right pulmonary artery in the left; secondly the right common carotid artery, followed by the right subclavian artery. As referred by Knight and Edwards (4), many intracardiac anomalies have been described associated with the second type, for example, the tetralogy of Fallot or the ventricular septal defect. The third type could be explained by the regression after the left subclavian artery. This is a less common finding, having a left aortic arch too, placed between the left common carotid and the left subclavian arteries proximally and behind the attachment of the left ligamentum arteriosum. The left subclavian artery has no connection with the aorta but it is attached to the left pulmonary trunk by a left ligamentum arteriosum. This situation may lead to a subclavian syndrome. The case presented had a normal rise of the aortic branches, although the position of the left subclavian artery was unusual, as a retroesophageal arterial trunk in a right-sided aortic arch. Occasionally, the aberrant position of the left subclavian artery may give rise to difficulty in swallowing. This is so-called "dysphagia lusoria" (lusoria meaning a prank of nature), but no such symptoms are referred in the present case. These aberrant cardiovascular patterns are rarely associated with symptoms. In fact, they might be detected and described occasionally, if the patient underwent diagnostic procedures for unrelated causes. Some X-ray films of the chest are suggestive of a the presence of a right aortic arch; namely, the lack of the aortic knob, the deviation of the trachea on the right or the indentation of the posterior esophageal wall after the administration of barium meal. In some cases, as studied by Sakalihassan et al. (5), aortography permitted an assesment of the position of the aortic arch, but its relationship with other structures has not been documented. On the other hand, the CT scan technique was useful because it visualized the anatomical pattern of the vessels and their relationship with the internal organs, as in our case. In fact, the CT scan allows a definite view of possible anomalies and the connection among the neighboring structures. Other imaging techniques may also be used: MRI, for instance, may add useful information for analysis of the anatomy of the cardiac and great vessels. A knowledge of the various kinds of anomalies that may affect the aortic arch and its branches is essential for the thoracic surgeon in order to avoid major complications, as well as to physicians performing procedures such as needle biopsies or injection. Moreover, some symptoms could occasionally be explained by postulating and detecting the presence of an anatomical variation.