An isolated left common carotid artery from the main pulmonary artery: possible malseptation of the truncoaortic sac.

An isolated left common carotid artery (LCA) is an extremely rare condition with only four reported cases. In each case, the isolated carotid artery connects to the right or left pulmonary artery via the ductus arteriosus and the embryologic basis for the abnormalities is believed to reflect an error in the development of the branchial arches. We present a case of an isolated LCA connecting to the main pulmonary artery in association with a right aortic arch and an anomalous origin of the left subclavian artery from the descending aorta. The left ligamentus arteriosus was identified separately. This may represent a disturbance in the septation of the truncoaortic sac secondary to abnormal migration of neural crest cells rather than a pure developmental anomaly of the branchial arches.