ABSTRACT
Aortic arch anomalies refer to congenital abnormalities of the position or branching pattern of the aortic arch alone or in combination. While certain aortic arch anomalies are asymptomatic, others may encircle the trachea and/or esophagus completely (vascular ring) or partially (vascular sling) and cause variable compression of these structures. Aortic arch anomalies are often associated with other congenital cardiac defects and/or chromosomal abnormalities, such as chromosome 22q11 deletion.2,3
Hypothetical double-arch model Understanding embryogenesis and fetal circulation is essential in understanding the pathology and pathophysiology of aortic arch anomalies.4 Normal and abnormal aortic arch development can be easily understood by reference to the hypothetical double aortic arch model introduced by the frontier pathologist, Dr. Jesse E. Edward in 1948.5,6 The model (Figure 31.2) illustrates a fairly late stage of development in that the aortic sac has been divided into the ascending aorta and pulmonary arterial trunk, and the descending aorta occupies a neutral position.7 Two aortic arches connect the ascending and descending aorta, forming a complete vascular ring around the trachea and esophagus. Each aortic arch gives rise to an ipsilateral common carotid artery, a subclavian artery, and an arterial duct that connects the distal part of the aortic arch to the adjacent branch pulmonary artery. Normally, the left aortic arch and left arterial duct persist, while the right aortic arch distal to the origin of the right subclavian artery and the right ductus regress (Figure 31.3a). As a result, the proximal part of the embryological right aortic arch becomes the right brachiocephalic (innominate) artery that bifurcates into the right common carotid and subclavian
arteries. Most of the malformations showing abnormal position and branching of the aortic arch are assumed to result from abnormal persistence of a part or parts that should have regressed and/or from abnormal regression of a part or parts that should have persisted.5,6
1. The left-or right-sidedness of the aortic arch relative to the trachea and main bronchus
2. The branching pattern of the head and neck arteries of the aortic arch; determining the absence or presence of an aberrant artery arising from the descending aorta and having a retroesophageal course
3. The left-or right-sidedness of the patent or ligamentous ductus arteriosus
Left aortic arch A left aortic arch refers to an aortic arch that is located on the left side of the trachea and arches over the proximal part of the left main bronchus. It is formed by interruption of a segment of the embryological right aortic arch. Interruption of the right arch distal to the origin of the right subclavian artery results in a normal left aortic arch (Figure 31.3). Interruption of the right arch between the origins of the right common carotid and right subclavian artery leaves the right subclavian artery attached to the distal part of the right aortic arch. As a consequence, the distal part of the embryological right aortic arch and right subclavian artery together constitute the aberrant right subclavian artery of the developed aortic arch (Figure 31.4).7-11 With interruption of the right aortic arch proximal to the origin of the right common carotid artery, the distal part of the right aortic arch will persist as the aberrant right innominate artery that gives rise to the right subclavian and right common carotid arteries. Each of these three forms of left aortic arch may have either left or right ductus arteriosus. Bilateral arterial ducts are exceedingly rare. When the left aortic arch has a normal branching pattern of the head and neck branches, no vascular ring or sling is formed around the trachea and esophagus
regardless of the presence of a left or right ductus arteriosus. When there is an aberrant origin of the right subclavian or innominate artery, the aberrant artery has an oblique retroesophageal course. When the right ductus is present between the aberrant artery and the right pulmonary artery, a complete vascular ring is formed around the trachea and esophagus. The ring consists of the ascending aorta, the left aortic arch, the descending aorta, the aberrant right subclavian or innominate artery, the right ductus arteriosus, the right pulmonary artery, and the pulmonary arterial trunk with the underlying heart completing the circle. When the left ductus arteriosus persists instead, the circle is not completed, and a vascular sling is formed around the left side of the trachea and esophagus.
