Brachiocephalic artery

The brachiocephalic artery, also known as the innominate artery, is a major vessel of the systemic circulation that arises from the aortic arch. It supplies blood to the right side of the head, neck, and upper limb through its terminal branches. Understanding its anatomy, relations, and clinical importance is crucial in vascular medicine and surgery.

Gross Anatomy of the Brachiocephalic Artery

Origin

The brachiocephalic artery originates as the first and largest branch of the aortic arch. It arises posterior to the manubrium of the sternum, slightly to the left of the midline, and ascends obliquely upward and to the right.

Course and Termination

The artery travels upward and to the right, crossing in front of the trachea. It is relatively short, measuring approximately 4 to 5 cm in length. The brachiocephalic artery terminates at the level of the right sternoclavicular joint, where it divides into:

• Right common carotid artery – supplying the right side of the head and neck.
• Right subclavian artery – supplying the right upper limb, thoracic wall, and parts of the neck.

Relations

The brachiocephalic artery lies in close association with several important anatomical structures, which are grouped as follows:

• Anterior Relations: Left brachiocephalic vein, sternohyoid and sternothyroid muscles, thymus (in children).
• Posterior Relations: Trachea, esophagus, and left recurrent laryngeal nerve.
• Lateral Relations: Right brachiocephalic vein, superior vena cava, right phrenic nerve, and vagus nerve.
• Superior and Inferior Relations: Superiorly continuous with the right common carotid and subclavian arteries; inferiorly related to the aortic arch.

Branches

Right Common Carotid Artery

This terminal branch ascends in the neck without branching in its cervical portion until it divides into the external and internal carotid arteries. It is responsible for supplying arterial blood to the right side of the head and neck.

Right Subclavian Artery

The right subclavian artery continues laterally and arches over the first rib to enter the axilla as the axillary artery. It provides branches to the thorax, neck, and upper limb, playing a vital role in systemic circulation to the right arm.

Other Minor Branches

The brachiocephalic artery generally has no additional branches before its bifurcation. However, in rare cases, small twigs to the thymus or mediastinal structures may arise. Anatomical variations such as early branching of the vertebral or thyroid arteries have been reported but are uncommon.

Embryological Development

Derivation from Aortic Arch System

The brachiocephalic artery develops from the embryonic aortic arch system. Specifically, it originates from the right horn of the aortic sac and the proximal part of the right fourth aortic arch. Its development ensures a vascular connection to the right common carotid and right subclavian arteries, which ultimately supply the right head, neck, and upper limb.

Developmental Variations

During embryogenesis, alterations in regression or persistence of aortic arches can lead to variations in the branching pattern of the aortic arch. For example, an abnormal persistence of vascular channels may result in a common trunk for all three major branches of the arch, while incomplete regression can give rise to aberrant subclavian arteries.

Variations and Anomalies

Absence or Duplication

Although extremely rare, the brachiocephalic artery may be absent, in which case the right common carotid and right subclavian arteries arise separately from the aortic arch. Duplication of the artery has also been reported, though it is exceedingly uncommon.

Aberrant Origin of Subclavian Artery

One of the most clinically significant anomalies is the aberrant origin of the right subclavian artery, which may arise directly from the distal aortic arch. This condition, known as arteria lusoria, can pass posterior to the esophagus, occasionally causing dysphagia (dysphagia lusoria) due to compression.

Common Trunk Variations

In some individuals, the brachiocephalic artery shares a common origin with the left common carotid artery, creating a two-branch aortic arch pattern. This is one of the most frequent variations observed in imaging and cadaveric studies, with important implications for vascular and endovascular procedures.

Histology

Wall Layers

The brachiocephalic artery, like other large elastic arteries, is composed of three main layers:

• Tunica intima: The innermost layer consisting of a single layer of endothelial cells supported by a thin subendothelial connective tissue layer. This layer provides a smooth lining that facilitates laminar blood flow.
• Tunica media: The thickest layer, composed of multiple concentric sheets of elastic lamellae interspersed with smooth muscle cells and connective tissue. The elasticity of this layer allows the vessel to withstand high pressures generated by the heart.
• Tunica adventitia: The outermost connective tissue layer containing fibroblasts, collagen fibers, nerves, and the vasa vasorum, which supply the outer part of the arterial wall with blood.

Elastic Properties

The brachiocephalic artery exhibits prominent elastic properties due to the presence of abundant elastic lamellae in the tunica media. These elastic features enable the vessel to accommodate the pulsatile output of the left ventricle and help maintain continuous blood flow during diastole. Degeneration or disease affecting the elastic fibers can predispose the artery to aneurysmal dilatation or other vascular disorders.

Relations to Neighboring Structures

Trachea

The brachiocephalic artery crosses anterior to the trachea in its thoracic portion. This relationship is clinically important in tracheostomy procedures and in cases of enlarged arteries compressing the airway.

Esophagus

Posterior to the artery lies the esophagus. Although separated by connective tissue, variations in the artery’s course or dilatation due to aneurysm can result in esophageal compression, sometimes leading to dysphagia.

Thymus and Sternum

In infants and young children, the thymus partly covers the artery anteriorly. In adults, the artery is situated posterior to the manubrium of the sternum, making surgical access challenging and requiring careful dissection during sternotomy.

Venous Structures

The left brachiocephalic vein crosses anterior to the artery, while the superior vena cava lies to its right. These venous relations are significant during central venous catheterization and cardiothoracic surgical procedures, where injury to the artery can cause serious complications.

Blood Supply and Anastomoses

Contribution to Head and Neck

The brachiocephalic artery contributes indirectly to the arterial supply of the head and neck through its terminal branch, the right common carotid artery. This vessel later divides into the external and internal carotid arteries, providing extensive branches to the face, scalp, brain, and cervical structures.

Contribution to Right Upper Limb

The right subclavian artery, another terminal branch of the brachiocephalic artery, is the main source of blood for the right upper limb. It also provides branches to the thoracic wall, vertebral column, and spinal cord via the vertebral artery and other collateral vessels.

Collateral Circulation

Collateral circulation involving the brachiocephalic artery and its branches ensures continuous perfusion even in the presence of arterial obstruction. Key anastomotic pathways include:

• Connections between the vertebral arteries and the circle of Willis at the base of the brain.
• Anastomoses between branches of the subclavian artery and intercostal arteries of the thoracic wall.
• Cervical anastomoses involving branches of the thyrocervical and costocervical trunks.

Clinical Significance

Aneurysms of the Brachiocephalic Artery

Aneurysmal dilatation of the brachiocephalic artery, although rare, poses a high risk of rupture and compression of adjacent structures such as the trachea or esophagus. Symptoms may include cough, dyspnea, and dysphagia. Surgical repair or endovascular stenting is often required.

Stenosis and Occlusive Disease

Atherosclerotic changes can lead to narrowing of the artery, resulting in reduced perfusion to the right side of the head and upper limb. Patients may present with neurological symptoms, vertigo, or ischemic limb manifestations. Angioplasty and stenting are common interventional treatments.

Trauma and Iatrogenic Injury

Due to its anterior location in the superior mediastinum, the brachiocephalic artery is vulnerable to penetrating trauma. It may also be inadvertently injured during surgical or interventional procedures, particularly central venous catheter placement. Such injuries can cause life-threatening hemorrhage.

Compression of Adjacent Structures

Enlargement of the artery, whether due to aneurysm or anatomical variation, may compress the trachea, esophagus, or veins. This can result in airway obstruction, dysphagia, or venous congestion. Careful imaging and timely management are necessary to prevent severe complications.

Radiological Evaluation

X-ray Findings

Plain chest radiographs may occasionally reveal an enlarged brachiocephalic artery as a widening of the mediastinum or abnormal soft tissue shadow. However, X-rays are not highly sensitive for detailed arterial assessment and are usually supplemented by advanced imaging techniques.

CT Angiography

Computed tomography angiography (CTA) provides detailed cross-sectional and three-dimensional visualization of the brachiocephalic artery. It is widely used for detecting aneurysms, stenosis, and traumatic injuries. CTA also allows accurate mapping of variations before surgical or endovascular interventions.

MRI Angiography

Magnetic resonance angiography (MRA) offers excellent soft tissue contrast without ionizing radiation. It is useful for evaluating vessel wall integrity, intraluminal thrombus, and flow dynamics. MRA is often preferred in younger patients or in those requiring repeated imaging.

Ultrasound and Doppler Studies

Duplex ultrasonography with Doppler flow analysis can assess blood flow velocity and detect stenosis in the proximal right common carotid and subclavian arteries, indirectly reflecting brachiocephalic artery pathology. It is a non-invasive, cost-effective tool but is limited by operator dependency and body habitus.

Surgical and Interventional Considerations

Surgical Exposure and Approaches

Access to the brachiocephalic artery is achieved via a median sternotomy or suprasternal approach, depending on the pathology. Careful dissection is required due to its proximity to the trachea, esophagus, and major veins.

Bypass and Grafting

In cases of significant stenosis or occlusion, bypass grafting may be performed using autologous vein grafts or synthetic conduits. Surgical reconstruction is sometimes necessary for complex aneurysms or traumatic injuries.

Endovascular Interventions

Minimally invasive approaches such as stenting and balloon angioplasty are increasingly used for treating stenosis and aneurysmal dilatation. Endovascular repair offers shorter recovery times and reduced perioperative risk compared to open surgery, although long-term outcomes require careful follow-up.

References

1. Standring S, ed. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2021.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Wolters Kluwer; 2018.
3. Drake RL, Vogl W, Mitchell AWM. Gray’s Anatomy for Students. 4th ed. Elsevier; 2019.
4. Skandalakis JE, Skandalakis LJ, Skandalakis PN. Surgical Anatomy and Technique: A Pocket Manual. 4th ed. Springer; 2014.
5. Sato K, Sato T. Variations in branching patterns of the aortic arch in Japanese patients. Anat Sci Int. 2019;94(3):200-210.
6. Illig KA, Doyle AJ. Aneurysms of the brachiocephalic artery: A review of literature and case report. J Vasc Surg. 2009;49(1):222-226.
7. Wang Z, Liu C, Zhao Z, et al. Endovascular management of brachiocephalic artery aneurysms: Outcomes and mid-term follow-up. Eur J Vasc Endovasc Surg. 2017;54(2):183-189.
8. Baldwin ZK, Comerota AJ. Brachiocephalic artery stenosis and occlusion: Clinical presentation and treatment options. Semin Vasc Surg. 2011;24(1):26-31.