Incomplete double aortic arch with Kommerell diverticulum
This anomaly results when a segment of the left arch in the embryologic double aortic arch undergoes atresia rather than complete involution between left subclavian artery distal to the left ductus arteriosus and the descending aorta. Now the left innominate artery is seen arising from left arch, followed by the right common carotid and right subclavian artery arising from right arch.
Kommerell diverticulum is remnant of left 4th aortic arch which does not undergo complete involution and in this case, it is basically residual distal atretic segment.
Differential Diagnosis is right aortic arch with mirror image branching which can be ruled out by looking at the position of descending aorta which is positioned on right side in right arch variant and on left side in this case.