Brachiocephalic Trunk

The brachiocephalic trunk, also known as the brachiocephalic artery or innominate artery, is the first and largest branch of the aortic arch. It plays a crucial role in supplying oxygenated blood to the right side of the head, neck, and upper limb. It is unique in that it exists only on the right side of the body; there is no corresponding vessel on the left.

Location and Origin

The brachiocephalic trunk arises from the aortic arch in the superior mediastinum. It originates posterior to the manubrium of the sternum and slightly anterior to the trachea. It is the most proximal of the three main branches of the aortic arch, emerging to the right of the midline before ascending and bifurcating behind the right sternoclavicular joint.

The artery ascends obliquely upward and to the right, crossing the anterior surface of the trachea, and then divides into two terminal branches: the right common carotid artery and the right subclavian artery.

Course

• Originates from the aortic arch just to the left of the midline
• Passes upward and to the right, anterior to the trachea
• Reaches the posterior aspect of the right sternoclavicular joint
• Bifurcates into the right subclavian artery and right common carotid artery

The brachiocephalic trunk is relatively short, typically measuring around 4 to 5 cm in length. It does not give off any named branches before bifurcation, though small unnamed branches may occasionally arise.

Terminal Branches

1. Right Common Carotid Artery

This branch ascends within the neck, lateral to the trachea and esophagus, to supply the right side of the head and neck. It terminates at the level of the thyroid cartilage, where it bifurcates into the internal and external carotid arteries.

2. Right Subclavian Artery

The right subclavian artery arches laterally toward the upper limb. It travels posterior to the anterior scalene muscle and gives off major branches including the vertebral artery, internal thoracic artery, and thyrocervical trunk, among others.

Anatomical Relationships

Anterior to the Brachiocephalic Trunk

• Manubrium of the sternum
• Left brachiocephalic vein (crosses obliquely from left to right)
• Thymus (in infants and young children)

Posterior to the Brachiocephalic Trunk

• Trachea
• Esophagus (further posterior)

To the Right

• Right brachiocephalic vein
• Superior vena cava

To the Left

• Left common carotid artery (second branch of the aortic arch)
• Vagus nerve (descends between the common carotid and subclavian arteries)

Surface Anatomy

The brachiocephalic trunk lies deep to the upper part of the manubrium and cannot be directly palpated. However, its location corresponds roughly to the level of the right sternoclavicular joint, where it bifurcates. Its course is oblique and anterior to the trachea in the lower cervical and upper thoracic regions.

Function

The brachiocephalic trunk functions as a primary conduit of oxygenated blood from the aorta to the right side of the head, neck, and upper extremity. It ensures symmetrical distribution of blood to both sides of the body despite its unilateral presence.

Through its terminal branches, it indirectly supplies:

• Right side of the brain via the internal carotid artery (from the right common carotid)
• Extracranial structures of the face and scalp via the external carotid artery
• Right upper limb and parts of the thoracic wall via the subclavian and its branches

Embryological Development

Embryologically, the brachiocephalic trunk is derived from the aortic sac, a structure that forms part of the early arterial system. It develops from the proximal part of the right fourth aortic arch and a portion of the aortic sac that connects the truncus arteriosus to the dorsal aorta. The asymmetrical formation of the great vessels results in a brachiocephalic trunk only on the right side of the body.

Variations

While the classic branching pattern is most common, anatomical variations of the brachiocephalic trunk exist, including:

• Common origin of the brachiocephalic and left common carotid arteries (bovine arch)
• Presence of a retroesophageal or retrotracheal brachiocephalic trunk (rare)
• Trifurcation into the right common carotid, right subclavian, and a third accessory branch