Absence of the Left Common Carotid Artery with Cervical Origin of the Right Subclavian Artery

The right ductus caroticus (arrow), the right seventh intersegmental artery and the right dorsal aorta below the level of the third arch form the right subclavian artery arising from right common carotid artery. Persistence of ductus caroticus with regression of third arch or fourth arch causes the internal and external carotid arteries to arise from the aortic arch on the left side. DC, ductus caroticus; 1 to 4, aortic arches (arrows).