Friday, September 28, 2012

The Cow Vessels

A common variant of the aortic arch is when the innominate artery and left common carotid artery arise from the same trunk, often misnamed the "bovine arch."

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)

43Y M, CT of the chest with contrast: There is an incidental common origin of the innominate / brachiocephalic artery and the left common carotid artery.  The two share a common trunk, which differentiates this from the variant in which the left common carotid arises directly off the innominate (normal-sized innominate origin).

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.

On the original radiograph, rightward deviation of the trachea was noted (green arrow).  On a follow-up CT, the deviation was seen to be due to mass effect from a T-shaped bifurcation of an innominate artery variant (green arrow) in which the left common carotid arises from the proximal innominate (not a common origin).

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 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