This configuration is reported in 13% of patients. It is reported to have an ethnicity difference, occurring in 25% of African-Americans and 8% of Caucasians.
|What is usually erroneously called the "bovine arch": a common origin of the innominate artery and left common carotid. (ref 1)|
Also possible is a variant configuration in which there is no common trunk, and the left common carotid arises off the innominate artery (below). This is reported to occur in 9% of the population.
Why would reporting these variants matter? It probably doesn't most of the time and usually is merely a matter of accurately describing what one is seeing on CT or angiography. One situation in which the distinction might be significant could be with an intervention for an innominate artery injury. If the anterior cerebral circulation is potentially threatened by the injury, the interventional approach might be modified.
So what is a true bovine arch? In cows and buffalo, all the great vessels arise off the aorta from a single trunk. This long single trunk seems to be an adaptation related to the long distance from the aortic arch to the thoracic inlet in these animals (below).
|What a true "bovine arch" would look like. This is rarely, if ever, seen in humans. (ref 1)|
1. Laytona KF, Kallmesa DF, Clofta HJ, et al. Bovine Aortic Arch Variant in Humans: Clarification of a Common Misnomer. AJNR August 2006 27: 1541-1542
2. Mauney MM, Cassada DC, Kaza AK, et al. Management of Innominate Artery Injury in the Setting of Bovine Arch Anomaly. Ann Thorac Surg 2001;72:2134–6