In the human circulatory system, a left brachiocephalic artery is not typical. While a significant vessel known as the brachiocephalic artery exists, it is generally found only on the right side of the body. This article clarifies why a distinct left brachiocephalic artery is absent in most individuals and discusses common variations.
The Aortic Arch: Standard Branching
The aorta, the body’s largest artery, emerges from the heart and forms a curved segment known as the aortic arch. This arch is the origin point for the major arteries that deliver oxygenated blood to the head, neck, and upper limbs. Typically, three main arteries branch from the superior aspect of the aortic arch. These are, in order from right to left, the brachiocephalic artery, the left common carotid artery, and the left subclavian artery.
The brachiocephalic artery is the first of these branches, supplying blood to the right side of the head, neck, and upper limb. The left common carotid artery then arises directly from the aortic arch, providing blood to the left side of the head and neck. The third typical branch is the left subclavian artery, which supplies the left upper limb.
The Brachiocephalic Artery: A Right-Sided Vessel
The brachiocephalic artery, also known as the brachiocephalic trunk or innominate artery, is a solitary vessel in most individuals. It arises as the first branch from the aortic arch, located in the upper right side of the chest. This artery is relatively short, typically measuring about 4 to 5 centimeters in length.
Soon after its origin, the brachiocephalic artery divides into two main branches: the right common carotid artery and the right subclavian artery. The right common carotid artery supplies blood to the right side of the head and neck. The right subclavian artery provides arterial blood to the right upper limb.
Why No Separate Left Brachiocephalic Artery?
The absence of a separate left brachiocephalic artery is a defining characteristic of the typical human aortic arch anatomy. On the left side of the body, the major arteries supplying the head, neck, and upper limb do not originate from a single common trunk. Instead, the left common carotid artery and the left subclavian artery arise directly and independently from the aortic arch.
This differs significantly from the right side, where the brachiocephalic artery serves as a shared origin for the right common carotid and right subclavian arteries. The left common carotid artery emerges as the second branch from the aortic arch, with the left subclavian artery arising as the third distinct branch. This direct branching pattern for the left-sided vessels eliminates the need for a separate left brachiocephalic trunk.
Variations in Aortic Arch Anatomy
While the three-branch pattern is most common, occurring in approximately 65% to 86% of individuals, anatomical variations of the aortic arch branching can occur. One frequently observed variation is referred to as a “bovine arch.” In this human variant, the brachiocephalic artery and the left common carotid artery share a common origin from the aortic arch. This configuration is found in about 10% to 20% of the population.
Another variation includes an aberrant right subclavian artery, which arises directly from the aortic arch as the last branch, rather than from the brachiocephalic artery. This aberrant artery typically crosses behind the esophagus to reach the right arm and occurs in about 1% to 2% of individuals. Less common variations can involve the aortic arch giving rise to four distinct branches or, conversely, only two branches, reflecting the complex embryological development of these vessels.