THE FORMAL PATHOGENESIS OF ISOLATED COMMON CAROTID OR INNOMINATE ARTERIES - THE CONCEPT OF MALSEPTATION OF THE AORTIC SAC

Deficient connections (= isolation) of the innominate artery or the co mmon carotid artery to the aorta are rare congenital anomalies of the human aortic arch complex that are usually associated with a patent va scular connection between the isolated artery and a pulmonary artery. In the present study we demonstrate chick fetuses with a corresponding anomaly, the isolation of the brachiocephalic artery. In our chick fe tuses the left brachiocephalic artery did not arise from the aortic ar ch, but was connected to the pulmonary trunk proximal (upstream) to th e patent left and right ductus arteriosus. These cases are of interest because the presence of a congenital pulmonary-systemic arterial conn ection proximal (upstream) to the ductus arteriosus cannot be explaine d by the traditional concept of the morphogenesis of the aortic arch c omplex. The development of the normal and abnormal branching patterns of the aortic arch arteries is traditionally explained by transformati on of the primitive embryonic pharyngeal arch arterial system due to o bliteration of some of its vascular segments. Based on this concept, t he isolation of an aortic arch artery can be explained by obliteration of vascular segments proximal and distal to this artery, whereas its connection to a pulmonary artery can be explained only by deficient ob literation (persistence) of the distal portion of the right or left si xth pharyngeal arch artery. The connecting ''vascular segment'' betwee n an isolated aortic arch artery and the pulmonary circulation, theref ore, is traditionally interpreted as a patent ductus arteriosus. The f ormal pathogenesis of congenital pulmonary systemic arterial connectio ns proximal (upstream) to the ductus arteriosus is discussed. The pres ented cases of isolation of the brachiocephalic artery are explained b y disturbances in the partition of the embryonic aortic sac, possibly due to abnormal development of the ''cardiac'' neural crest.