FIG 47.6 (A) Morphogenesis (left) fetal arrangement (middle) and postnatal structure of left aortic arch (LAA) with aberrant origin of the right subclavian artery and left-sided arterial duct In the hypothetical model, the red bars again indicate the segments that regress In the fetal and postnatal circulations, a vascular sling is formed on the left side of the trachea and esophagus (B) Computed tomograms show an LAA and aberrant right subclavian artery arising from the descending aorta, with no intervening diverticulum of Kommerell The posterior wall of the trachea shows a shallow indentation from the aberrant right subclavian artery (right) LCCA, Left common carotid artery; LPA, left pulmonary artery; LSA, left subclavian artery; MPA, main pulmonary artery; RAA, right aortic arch; RCCA, right common carotid artery; RPA, right pulmonary artery; RSA, right subclavian artery FIG 47.7 Derivation and structures of left aortic arch (LAA) with aberrant right subclavian artery when the arterial duct is right sided In the hypothetical model, the red bars again indicate the segments that regress In the fetal circulation (middle), the LAA, the distal remnant of the right aortic arch (RAA), the right-sided arterial duct, and the pulmonary trunk produce an L-shaped vascular loop around the trachea and esophagus Because the two limbs of the L-shaped loop are attached to the heart, there is a complete vascular ring In the postnatal circulation (right), subsequent to closure of the arterial duct, the proximal part of the aberrant right subclavian artery, representing the distal remnant of the RAA, persists as a diverticulum of Kommerell Note that, as with the previous situation, the flow in the distal remnant of the RAA switches its direction after birth LCCA, Left common carotid artery; LPA, left pulmonary artery; LSA, left subclavian artery; MPA, main pulmonary artery; RCCA, right common carotid artery; RPA, right pulmonary artery; RSA, right subclavian artery A right-sided aortic arch with a mirror-image branching results from abnormal regression of the left aortic arch distal to the origin of the left subclavian artery (Fig 47.8A and B) This anomaly of the aortic arch only rarely forms a vascular ring regardless of the sidedness of the arterial duct In this pattern, the persisting arterial duct is usually on the left, connecting the base of the left brachiocephalic artery to the left pulmonary artery.29 Less commonly, the arterial duct is either on the right or bilateral Rarely, the arterial duct arises from the descending aorta on the right side and takes a retroesophageal course to connect to the left pulmonary artery.3,6,29–32 This is the only combination that constitutes a complete vascular ring in the presence of mirror-image branching (Fig 47.9) The anomaly results from abnormal regression of the left aortic arch distal to the origin of the left subclavian artery and proximal to the insertion of the persisting left arterial duct, with regression of the right arterial duct The distal left aortic arch remnant persists as a diverticulum of Kommerell FIG 47.8 (A) Morphogenesis, fetal arrangement, and postnatal structure of a right aortic arch (RAA) with mirror-image branching, the red bars in the hypothetical model indicating the segments that regress In the majority of cases, it is the arterial duct on the left side that persists, with regression of the left aortic arch (LAA) distal to the origins of the left subclavian artery (LSA) and the left arterial duct, along with the right-sided arterial duct In the postnatal circulation, the left-sided arterial ligament connects the base of the left brachiocephalic or subclavian artery to the left pulmonary artery (LPA) Persistence of the right-sided arterial duct is uncommon (B) The computed tomograms, seen from above and the front, show the aortic arch on the right side of trachea The aortic arch gives rise to the left brachiocephalic artery (LBA), right common carotid artery (RCCA), and right subclavian artery in sequence The expected location of the ligamentous arterial duct is marked by a red bar (right) Note that the LSA kinks inferiorly and the LPA is mildly stenotic, both highly suggestive of the presence of a left-sided arterial ligament LCCA, Left common carotid artery; LIA, left innominate artery; MPA, main pulmonary artery; RPA, right pulmonary artery; RSA, right subclavian artery; SCV, superior caval vein