A rare case with the absence of a distinct common brachiocephalic trunk in an adult mixed-breed horse

The only branch that detaches from the aortic arch of adult horses is the common brachiocephalic trunk. This report describes a rare case of the unusual arterial arrangement of the aortic arch in a female adult horse. The aortic arch was found to lack a common brachiocephalic trunk and had instead two branches, the first being a brachiocephalic trunk and the second being a left subclavian artery. The direct origin of the left subclavian artery from the aortic arch is very rare in horses and a similar case has not been reported previously. The potential embryologic and phylogenetic aspects of this variation are discussed.