Congenital anomalies of aortic arch take many forms. Often no symptoms result, and only presented as radiologic findings. But on occasion the anomaly may lead to major cardiovascular or respiratory symptoms. Five primary groups of anatomic arch anomalies are listed as following: 1) double aortic arch, 2) right aortic arch with mirror-image branching or abnormal branching, 3) Isolation of a subclavian artery, 4) left aortic arch with abnormal branching, and 5) Interruption of the aortic arch. The common anomalies are relatively easy to make a diagnosis, but the rare and complicated variants can be confusing. Therefore, understanding the normal development and associated developmental errors is helpful for correct radiology interpretation.

Normal Development

During the embryologic development, six pairs of the vascular arches connect the ventral aorta with the paired dorsal aorta. These vascular arches are numbered 1 to 6 in cephalocaudal order (Fig. 1A). The first, second, and fifth arches regress. The ventral aorta with the third arches form the common carotid arteries (CCAs). Cephalad continuation of the right and left dorsal aortae form the internal carotid arteries (ICAs). The external carotid arteries sprout from the proximal CCAs. The fourth arch forms the aortic arch and the proximal sixth arches become the pulmonary arteries. The distal right sixth arch disappears and the distal portion of the left sixth arch forms the patent ductus arteriosus. Bilateral C7 intersegmental arteries enlarge to become subclavian arteries (Fig. 1B).

The double aortic arch hypothesis of Edwards

The hypothetical double-aortic arch system of Edwards is useful to understand the aortic arch anomalies. It is said that there are the double aortic arch with the ductus arteriosus on each side encircling the trachea and esophagus. Each CCA and subclavian artery arises from the ipsilateral aortic arch. The descending aorta is in the midline (Fig. 2A). The regressions occurred in various portion at the two aortic arches result in different types of abnormalities of aortic arches. The normal left-sided aortic arch is regression of primitive right aortic arch beyond origin of right subclavian artery (Fig. 2B).