Author: Roberto Grujičić MD•Reviewer: Alexandru Andrușca MD, PhDLast reviewed: September 08, 2021Reading time: 7 minutes

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Internal thoracic artery (Arteria thoracica interna)

The internal thoracic artery (internal mammary artery) is a long, paired vessel that originates from the proximal part of the subclavian artery. It runs inferomedially and enters the thoracic cage deep to the clavicle and the first rib. Terminating at the level of the sixth rib, it divides into two terminal branches: superior epigastric and musculophrenic arteries.

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The internal thoracic artery gives rise to numerous branches that supply the skin and muscles of the anterior aspect of the thoracic cage and the superior part of the abdominal wall. Additionally, it provides blood supply for the breasts, parietal pleura, sternum, pericardium and thymus.

This article will discuss the anatomy and function of the internal thoracic artery.

Key facts about the internal thoracic artery
Origin Subclavian artery
Branches Anterior collaterals: Anterior intercostal branches Perforating branches Medial mammary arteriesPosterior collaterals: Mediastinal branches Thymic branches Pericardiacophrenic artery Sternal branches Bronchial branches Tracheal branchesTerminal branches: Superior epigastric arteryMusculophrenic artery
Supply Skin and muscles of the anterior aspect of the thoracic cage and superior aspect of the abdominal wall, typical ribs, breasts, parietal pleura, sternum, pericardium and thymus.

Contents
Branches and supply
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The internal thoracic artery originates from the first part of the subclavian artery. It arises as the second branch, proximal and inferior to the thyrocervical trunk and distal to the vertebral artery.

It then descends into the thoracic cage by taking an anteroinferior path, traveling posterior to the first costal cartilage and the clavicle. The artery runs inferiorly in an almost vertical manner, positioned close to the anterior chest wall and deep to the first six costal cartilages. The artery ends at the level of the sixth rib or sixth intercostal space, by splitting into two terminal branches: superior epigastric artery and musculophrenic arteries.

Relations 

The artery runs inside the thorax, sitting close to its anterior wall. At the level of the first rib, the vessel is crossed anteriorly by the phrenic nerve. It descends through the thorax, by traveling parallel to the lateral margin of sternum. The artery runs under the pectoralis major muscle and the first six costal cartilages.

Due to its anterior position within the thorax, the proximal segment of the artery (proximal to second or third costal cartilage) is separated from the parietal pleura by a strong layer of fascia and distally by the transversus thoracis muscle. The artery is accompanied, on its course, by the internal thoracic vein that lies medial to the artery.

Branches and supply


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The internal thoracic artery gives rise to numerous collateral branches that supply the following structures:

skin and muscles of the anterior aspect of the thoracic cageskin and muscles of the superior aspect of the abdominal wallbreastparietal pleurasternumtypical ribspericardiumthymus

Additionally, the branches of the internal thoracic artery split into three separate categories; anterior, posterior and terminal branches.

Anterior branches

Anterior branches include the anterior intercostal, perforating and medial mammary arteries.

Anterior intercostal branches diverge laterally from the internal thoracic artery to run into the first six intercostal spaces. They supply the intercostal, pectoral muscles and the adjacent skin, anastomosing with their posterior counterparts near the posterior trunk.

Posterior branches

Posterior branches include the following:Mediastinal and thymic branches: these are small branches which supply the connective tissues of the mediastinum, thymus and the anterior part of the pericardium.Pericardiacophrenic artery: arises at the first costal cartilage and descends, on both sides, along with the phrenic nerve till the diaphragm and supplies the pericardium and pleura.

Terminal branches

The internal thoracic artery terminates at the level of the sixth rib or the sixth intercostal space, dividing into two terminal branches: the musculophrenic and superior epigastric arteries.

To learn more about the nerves and vessels of the thoracic wall check out our other articles, videos, quizzes and labeled diagrams. 


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Neurovasculature of the thoracic wall Explore study unit

Anatomical variations

In terms of its origin and termination, the internal thoracic artery expresses relatively common variations. It can arise as a branch from the distal segment of the subclavian artery as a single vessel, or it can share a common origin with the thyrocervical trunk. In about 10-15% of cases, the terminal end of the internal thoracic exists as a trifurcation, with an additional branch supplying arterial blood to the inferior aspect of the sternum (xiphoid branch).

The presence of a lateral costal branch is a variation present in approximately 15-30% of cases. It usually originates at the proximal part of the internal thoracic. This vessel runs parallel and lateral to the internal thoracic artery. It can be present unilaterally or bilaterally. The lateral costal branch contributes to the supply of the thoracic wall.


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Show references

References:

Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.Netter, F. (2019). Atlas of Human Anatomy (7th ed.). Philadelphia, PA: Saunders.Standring, S. (2016). Gray"s Anatomy (41st ed.). Edinburgh: Elsevier Churchill Livingstone.Tubbs, R. S., Shoja, M. M., Loukas, M., & Bergman, R. A. (2016). Bergman’s comprehensive encyclopedia of human anatomic variation. Hoboken: Wiley Blackwell.

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