The internal thoracic artery, previously known as the internal mammary artery, is a branch of the subclavian artery. It supplies blood to the chest wall, breasts, and portions of the upper abdomen.
Location
The internal thoracic artery originates from the first part of the subclavian artery and descends vertically along the inner surface of the anterior thoracic wall. It runs parallel to the sternum, located approximately 1 to 2 centimeters lateral to it, and courses deep to the intercostal muscles and costal cartilages. It travels through the thoracic cavity on either side of the sternum and gives rise to multiple branches, including the pericardiophrenic artery, before bifurcating into the musculophrenic and superior epigastric arteries at the level of the sixth intercostal space.
Anatomy
Origin
The internal thoracic artery (formerly called the internal mammary artery) originates from the first part of the subclavian artery. The subclavian artery gives rise to several key branches that supply the thorax, neck, and upper extremities, and the internal thoracic artery is one of its major branches.
Course
After originating from the subclavian artery, the internal thoracic artery descends vertically along the inner surface of the anterior thoracic wall. It runs deep to the clavicle, just posterior to the sternoclavicular joint. As it continues its descent, it courses along the inner aspect of the ribs, approximately 1 to 2 centimeters lateral to the sternum.
The artery runs posterior to the costal cartilages of the first to sixth ribs, between the transversus thoracis muscle and the internal intercostal muscles. It continues its course inferiorly until it reaches the sixth intercostal space, where it bifurcates into its two terminal branches: the musculophrenic artery and the superior epigastric artery.
Relations
- Anteriorly: The internal thoracic artery is positioned deep to the anterior thoracic wall and the pectoralis major muscle. It also lies anterior to the costal cartilages of the ribs.
- Posteriorly: The artery is related to the parietal pleura and the lungs, and it runs posterior to the internal intercostal muscles. The transversus thoracis muscle also lies posterior to the artery along its course.
- Laterally: The internal thoracic artery is positioned lateral to the sternum and runs approximately parallel to it. The intercostal arteries and veins also lie laterally in relation to the artery as it descends along the thoracic wall.
Branches
The internal thoracic artery gives rise to several branches as it descends through the thoracic cavity:
- Pericardiophrenic Artery: This branch arises near the origin of the internal thoracic artery and descends alongside the phrenic nerve, supplying the pericardium and diaphragm.
- Anterior Intercostal Arteries: These arteries branch off the internal thoracic artery at each intercostal space from the first to the sixth. They run within the intercostal spaces, supplying the intercostal muscles, skin, and other structures of the anterior thoracic wall.
- Perforating Branches: These branches emerge through the intercostal spaces and supply blood to the overlying skin and pectoralis major muscle. In females, they also provide blood supply to the breasts.
- Musculophrenic Artery: One of the terminal branches of the internal thoracic artery, the musculophrenic artery follows the costal margin and gives rise to anterior intercostal arteries in the seventh through ninth intercostal spaces.
- Superior Epigastric Artery: The other terminal branch, the superior epigastric artery, descends into the anterior abdominal wall, supplying the rectus abdominis muscle and anastomosing with the inferior epigastric artery.
Termination
The internal thoracic artery terminates at the level of the sixth intercostal space, where it bifurcates into its two terminal branches:
- Musculophrenic artery: This artery continues along the costal margin and supplies the diaphragm, giving off anterior intercostal branches to the lower intercostal spaces.
- Superior epigastric artery: This artery continues downward into the rectus sheath of the anterior abdominal wall, supplying the rectus abdominis muscle and the upper part of the abdominal wall.
Anastomoses
The internal thoracic artery forms important anastomoses with other arteries in the thorax and abdomen:
- Anterior intercostal arteries: These arteries anastomose with the posterior intercostal arteries, which arise from the thoracic aorta.
- Superior epigastric artery: This artery anastomoses with the inferior epigastric artery, which arises from the external iliac artery, forming an important collateral blood supply to the anterior abdominal wall.
- Musculophrenic artery: The musculophrenic artery forms small anastomoses with the inferior phrenic arteries, which arise from the abdominal aorta and supply the diaphragm.
Variations
The course and branching pattern of the internal thoracic artery is relatively consistent, though anatomical variations can occur. In some individuals, the artery may give rise to additional branches that supply the sternum, thymus, or pericardium. Occasionally, the origin of the internal thoracic artery may vary slightly, and in rare cases, it may give rise to a dorsal scapular artery or other anomalous vessels. Variations in the size and prominence of the musculophrenic and superior epigastric arteries are also possible, although these are less common.
Function
The internal thoracic artery is a major vessel responsible for supplying oxygenated blood to the anterior thoracic wall, diaphragm, and upper portion of the anterior abdominal wall. Its branches nourish important muscles, skin, and vital structures such as the pericardium and diaphragm. Below is a detailed explanation of the key functions of the internal thoracic artery.
Blood Supply to the Anterior Thoracic Wall
The internal thoracic artery is the primary artery responsible for providing blood to the anterior thoracic wall, which includes the intercostal muscles, ribs, and overlying skin. Through its anterior intercostal arteries, it supplies the first six intercostal spaces, nourishing the intercostal muscles responsible for stabilizing and moving the rib cage during respiration. The artery also provides perforating branches that pierce through the intercostal muscles to supply the overlying skin, subcutaneous tissues, and in females, the mammary glands (breasts).
By supporting the thoracic muscles and skin, the internal thoracic artery plays a critical role in maintaining the structure and function of the chest wall, enabling both respiratory movement and protection of the thoracic organs.
Blood Supply to the Breast
The internal thoracic artery plays a significant role in supplying blood to the breast tissue, especially in females. Its perforating branches emerge through the intercostal spaces to supply the mammary glands, skin, and other connective tissues of the breast. These branches are particularly important for maintaining the vascular health of the breast and supporting its functional role in lactation.
In reconstructive surgery, such as after a mastectomy, the internal thoracic artery is often used for breast reconstruction through the deep inferior epigastric perforator (DIEP) flap or other flap procedures, where it provides a reliable blood source to the transplanted tissue.
Blood Supply to the Pericardium and Diaphragm
Through its pericardiophrenic artery, a key branch that accompanies the phrenic nerve, the internal thoracic artery supplies blood to the pericardium, which is the fibrous sac surrounding the heart, and the superior part of the diaphragm, the primary muscle responsible for breathing. The pericardiophrenic artery ensures that both the pericardium and diaphragm receive adequate oxygen and nutrients, supporting the health of the heart’s protective membrane and the diaphragm’s continuous function in respiration.
This supply is crucial for maintaining the pericardium’s ability to protect the heart from friction and excessive movement, while also ensuring the diaphragm’s efficiency during the inhalation and exhalation process.
Contribution to Collateral Circulation in the Thorax
The internal thoracic artery plays a vital role in forming collateral circulation within the thoracic region. Its anterior intercostal branches form important anastomoses with the posterior intercostal arteries, which arise from the thoracic aorta. This collateral network ensures that the intercostal muscles, ribs, and overlying tissues continue to receive blood even if there is an obstruction in the main arterial supply, such as in cases of atherosclerosis or trauma.
Additionally, the internal thoracic artery’s anastomotic network contributes to overall vascular redundancy, protecting against ischemic events in the chest wall and ensuring that the thoracic tissues remain well-vascularized even in cases of localized arterial damage or compression.
Blood Supply to the Anterior Abdominal Wall
The internal thoracic artery provides oxygenated blood to the anterior abdominal wall through its superior epigastric artery, one of its terminal branches. The superior epigastric artery descends into the rectus sheath, supplying the rectus abdominis muscle and other structures of the upper abdominal wall. This function is essential for maintaining the strength and functionality of the anterior abdominal muscles, which play a critical role in core stability, posture, and movements such as bending, twisting, and lifting.
The superior epigastric artery also forms an important anastomosis with the inferior epigastric artery, a branch of the external iliac artery. This anastomosis provides a robust blood supply to the anterior abdominal wall, ensuring continuous oxygenation and nutrient delivery to the abdominal muscles, fascia, and overlying skin.
Support for the Diaphragm
The internal thoracic artery’s terminal branch, the musculophrenic artery, plays a key role in supplying blood to the diaphragm. This artery follows the costal margin, giving off branches to the diaphragm and contributing to its vascularization, along with other arteries like the inferior phrenic artery. The diaphragm is a critical muscle for respiration, and its continuous contraction and relaxation require a steady supply of oxygenated blood to support respiratory function.
The musculophrenic artery also provides anterior intercostal branches to the lower intercostal spaces (7th to 9th), supplying blood to the intercostal muscles and thoracic structures along the lower rib cage.
Support for Reconstructive and Coronary Bypass Surgery
Although its primary functions are anatomical, the internal thoracic artery is frequently used in surgical procedures due to its long and reliable blood supply. In coronary artery bypass grafting (CABG), the internal thoracic artery is often harvested to bypass blocked coronary arteries because of its robust and durable blood flow. Its location and consistent blood supply make it one of the most commonly used arteries in this procedure, significantly improving the outcomes for patients with coronary artery disease.
In reconstructive surgery, particularly in the case of breast reconstruction following a mastectomy, the internal thoracic artery is used to provide blood to transplanted tissues in flap-based procedures, ensuring that the new tissue receives adequate blood supply for healing and integration.
Clinical Significance
The internal thoracic artery (formerly known as the internal mammary artery) is highly significant in both clinical and surgical settings due to its role in supplying the anterior chest wall, pericardium, diaphragm, and portions of the abdominal wall. Its branches contribute to critical vascular supply for the intercostal muscles, ribs, breasts, and upper abdominal muscles.
In coronary artery bypass grafting (CABG), the internal thoracic artery is one of the most preferred vessels for creating a bypass around blocked coronary arteries. Its robust and long-lasting blood flow makes it highly effective in improving cardiac outcomes for patients with coronary artery disease.
The artery is also important in breast reconstruction surgeries, particularly in flap-based procedures, where it is used to ensure that transplanted tissues receive an adequate blood supply. Its reliable vascularization in the thorax and upper abdomen also makes it crucial in maintaining collateral circulation in cases of trauma, surgery, or vascular occlusion. Understanding its anatomy is essential for surgeons to minimize complications in chest surgeries and ensure the proper function of critical structures.
