Origin of the left subclavian artery as the first branch and origin of the right subclavian artery as the fourth branch of the aortic arch with crisscrossing posterior to the common carotid arteries.

We describe an aortic arch anomaly consisting of the origin of the left subclavian artery as the fourth branch and the right subclavian artery as the first branch off the aortic arch with crisscrossing of these two arteries anterior to the trachea without clinical consequences. This anomaly, to our knowledge, has not been reported previously.