Internal thoracic artery
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.
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.
Anterior intercostal branches
Medial mammary arteries
Superior epigastric artery
|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.
- Origin and course
- Branches and supply
- Anatomical variations
Origin and course
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.
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.
Quiz yourself on the neurovasculature of the thoracic wall.
Branches and supply
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 cage
- skin and muscles of the superior aspect of the abdominal wall
- parietal pleura
- typical ribs
Additionally, the branches of the internal thoracic artery split into three separate categories; anterior, posterior and terminal 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.
- Perforating branches stem from the medial aspects of the internal thoracic artery. They have a short medial course along the inner surface of the superior six intercostal spaces. Accompanied by the cutaneous branches of the intercostal nerves, these arteries pierce through the internal intercostal muscles and emerge on the anterior surface of the thoracic cage. The perforating branches supply the superior six internal intercostal muscles, pectoralis major muscle and overlying skin.
- Medial mammary branches usually originate from the second to fourth perforating branches after piercing the intercostal muscles and supply the tissue of the breast. During high vascular demand (i.e. during lactation) these branches enlarge in diameter.
- 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.
- Perforating and sternal branches: together with bronchial and tracheal branches, these branches contribute to the vascularization of the corresponding structures of the mediastinum (thymus, pericardium, diaphragm, sternum, trachea and bronchi).
- Sternal and pericardiacophrenic arteries anastomose with the branches of the costocervical trunk to form the subpleural mediastinal plexus.
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.
- The musculophrenic artery runs in an inferolateral direction, terminating before reaching the last intercostal space. It provides two anterior intercostal branches that provide blood supply for the last three intercostal spaces. In its distal segment, it gives off branches for the pericardium and abdominal muscles.
- The superior epigastric artery is a distal continuation of the internal thoracic artery. It supplies the superior aspect of the rectus abdominis muscle. Upon appearing in the umbilical region, it anastomoses with the inferior epigastric artery.
To learn more about the nerves and vessels of the thoracic wall check out our other articles, videos, quizzes and labeled diagrams.
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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