FIG 48.10 Reanalyzed computed tomographic dataset from the patient shown in Fig 48.9B using virtual cardiac dissection technique (A) Frontal view shows external morphology (B) Short-axis view as seen from below shows arrangement of the vessels from inside The channel supplying the left pulmonary artery unequivocally arises distal to the brachiocephalic artery, making it more likely to represent a remodeled left-sided arterial duct, more so since it supplies the discontinuous left pulmonary artery Anomalous Origin of a Pulmonary Artery From the Ascending Aorta Other investigators have invoked persistence of the fifth arch artery to explain anomalous origin of the right or left pulmonary artery directly from the ascending aorta.29,34,55,63 Such interpretations do not reflect current knowledge concerning the development of the intrapericardial components of the arterial trunks The right and left pulmonary arteries develop within the pharyngeal mesenchyme, taking their origins from the sixth arch arteries as they exit from the floor of the aortic sac They would have no direct connection with a fifth arch artery should such an artery be present It is unequal separation of the aortic sac that results in anomalous connection of either of the right or left pulmonary artery to the ascending aorta rather than retaining its connection with the pulmonary trunk.9 The dubious nature of the evidence offered for persistence of a presumed artery of the fifth arch is further evidenced by reanalysis of the interpretations offered for cases having both anomalous origin of a pulmonary artery from the ascending aorta and a double-barreled aorta In the described instances of the cases of which we are aware, it was the left pulmonary artery that took its origin from the ascending aorta The double-barreled aorta was itself left-sided34,55 in two of the reported cases and right-sided in the other.29 These rare anatomic aberrations can be explained only on the basis of persistence of the artery of the fifth arch if the purported artery is either bilateral29 or is itself duplicated on the left side.34,55 Since the existence of a solitary fifth arch artery is in doubt, suggestions for existence of dual or bilateral fifth arch arteries are implausible Far better explanations are available on the basis of persistence of collateral channels for the double-barreled aorta and unequal separation of aortic sac for the anomalous origin of the pulmonary artery from the ascending aorta Unusual Forms of Systemic-to-Pulmonary Arterial Connections The lack of any connection of the pulmonary arteries with a channel that continues to supply the descending thoracic aorta has led some authors to argue that the channel itself is the fifth, rather than the sixth, arch artery These arrangements, however, can equally well be interpreted on the basis of a common arterial trunk with pulmonary dominance and interruption of the aortic arch, with the vessel in question indeed representing the persistent arterial duct (Fig 48.11A).71 In another patient, who had aortic atresia with interruption of the aorta beyond both carotid arteries and with aberrant retroesophageal origin of the right subclavian artery, the authors interpreted the channel connecting the right pulmonary artery to the diminutive ascending aorta as representing the persisting artery of the fifth arch The channel in question, nonetheless, takes its origin from a right-sided brachiocephalic artery and connects directly to the right pulmonary artery On the basis of probabilities, therefore, it is more likely that the vessel represents the right-sided arterial duct (see Fig 48.10B).23 We acknowledge, however, that in another report implicating the fifth arch artery, the anatomy is so unusual as to defy logical interpretation based on our current understanding of cardiac development.72 FIG 48.11 Two cases reported in the literature as representing persistence of the artery of the fifth pharyngeal arch (A) In this malformation, the channel connecting to the descending aorta was thus interpreted as fifth arch artery.71 (B) In this malformation the channel connecting the diminutive ascending aorta to the right pulmonary artery was interpreted as fifth arch artery.23 As this illustration shows, in both instances the channels could just as well, if not more likely, have represented the persistently patent arterial duct Abnormal Origin of Brachiocephalic Arteries Many investigators have interpreted abnormal arrangements of the origin of the brachiocephalic arteries from the ascending aorta or the aortic arch on the basis of persistence of fifth arch arteries (Table 48.3).77–107 As we have now shown, the arteries within the pharyngeal arches arising from the aortic sac undergo extensive remodeling during the embryonic period before attaining their final configuration (Figs 48.3 to 48.6), with the horns of the aortic sac itself providing the confluence of the arteries of the third and fourth arches Variations in the pattern of branching of the extrapericardial arteries from the aortic arch,