Internal thoracic veins

The internal thoracic veins are paired veins located along the inner surface of the thoracic cavity. They run vertically on both sides of the sternum, accompanying the internal thoracic arteries. These veins collect deoxygenated blood from the anterior chest wall and the upper abdominal region. The internal thoracic veins originate near the sixth intercostal space, where they receive blood from the superior epigastric and anterior intercostal veins. They ascend along the thoracic wall and eventually drain into the brachiocephalic veins on both sides of the neck, which then return blood to the superior vena cava and the heart.

Location

The internal thoracic veins are located on the inner surface of the anterior thoracic wall, running vertically on both sides of the sternum. These veins accompany the internal thoracic arteries, lying just lateral to them, and extend from the lower rib cage up to the root of the neck. They are enclosed within the thoracic cavity, along the posterior surface of the costal cartilages.

Anatomy

Origin

The internal thoracic veins originate at the level of the sixth intercostal space, where they begin as continuations of the superior epigastric veins. These veins drain the upper portion of the anterior abdominal wall, passing through the diaphragm before ascending into the thoracic cavity.^[6] The internal thoracic veins then ascend toward the base of the neck, collecting venous blood from several tributaries along the way.

Course

The internal thoracic veins ascend vertically within the thoracic cavity, running alongside the internal thoracic arteries. Their course follows the inner surface of the thoracic wall, passing anterior to the pleura (the membrane covering the lungs) and deep to the costal cartilages. As they travel upward, the veins receive blood from several smaller veins, including the anterior intercostal veins, which drain the intercostal spaces between the ribs. They continue their course superiorly, eventually reaching the root of the neck, where they empty into the brachiocephalic veins. The internal thoracic veins on the left and right sides follow a similar pathway and drain into their respective brachiocephalic veins.

Tributaries

The internal thoracic veins receive several tributaries during their course through the thoracic cavity:

• Anterior Intercostal Veins: These veins drain the anterior portion of the intercostal spaces and accompany the anterior intercostal arteries. Each internal thoracic vein receives multiple anterior intercostal veins as it ascends along the thoracic wall.
• Superior Epigastric Veins: The superior epigastric veins are the continuation of the internal thoracic veins in the lower part of the thorax.^[5] These veins drain the upper part of the anterior abdominal wall.
• Musculophrenic Veins: These veins drain the lower intercostal spaces and the diaphragm. They also serve as tributaries to the internal thoracic veins, typically joining near the sixth or seventh intercostal space.
• Pericardiophrenic Veins: These veins drain the pericardium (the sac surrounding the heart) and the diaphragm, running alongside the phrenic nerve. The pericardiophrenic veins typically empty into the internal thoracic veins near their midpoint.

Relations to Neighboring Structures

• Internal Thoracic Arteries: The internal thoracic veins run parallel to and slightly lateral to the internal thoracic arteries, forming a paired vascular system that supplies and drains the anterior thoracic wall.
• Costal Cartilages: The veins lie deep to the costal cartilages of the ribs, which protect them within the thoracic cavity. This position places the veins in close proximity to the ribs and the intercostal spaces.
• Pleura and Lungs: The internal thoracic veins lie just anterior to the pleura, which surrounds the lungs.^[3] This close relationship means that the veins are situated between the pleura and the inner surface of the chest wall.
• Diaphragm: At their lower end, the internal thoracic veins pass through the diaphragm, continuing as the superior epigastric veins. The diaphragm acts as an anatomical boundary between the thoracic and abdominal regions, and the veins pass through it near the midline.

Termination

The internal thoracic veins terminate by draining into the brachiocephalic veins. On the right side, the internal thoracic vein drains into the right brachiocephalic vein, while on the left side, it drains into the left brachiocephalic vein. These brachiocephalic veins then join to form the superior vena cava, which returns deoxygenated blood to the heart’s right atrium.

Variations

The anatomy of the internal thoracic veins is generally consistent, but some variations can occur.^[1] In some cases, the number and size of tributaries may vary, and occasionally, the veins may have additional small branches that drain into other nearby veins. The position and course of the internal thoracic veins are typically symmetric on both sides of the body, but individual anatomical differences may exist, particularly in the connections with the brachiocephalic veins.

Function

Venous Drainage of the Anterior Thoracic Wall

The primary function of the internal thoracic veins is to drain venous blood from the anterior thoracic wall. These veins collect deoxygenated blood from structures in the chest, including the intercostal muscles, ribs, and skin. The anterior intercostal veins, which drain the spaces between the ribs, empty into the internal thoracic veins, ensuring that blood is efficiently transported away from the thoracic wall and returned to the heart.

Drainage of the Anterior Intercostal Spaces

The internal thoracic veins are essential for the venous drainage of the intercostal spaces, specifically the anterior portions of these spaces.^[8] The anterior intercostal veins, which accompany the arteries in the intercostal spaces, drain blood from the muscles and tissues involved in respiration, such as the intercostal muscles. These veins allow for proper removal of deoxygenated blood from these active muscles, ensuring efficient respiration and circulation.

Venous Return from the Upper Abdominal Wall

The internal thoracic veins are continuous with the superior epigastric veins, which are responsible for draining blood from the upper abdominal wall. This connection allows the internal thoracic veins to contribute to the venous return from the abdominal wall, particularly from the rectus abdominis muscle and surrounding tissues. Blood from the superior epigastric veins is funneled into the internal thoracic veins, further supporting the return of blood to the heart.

Drainage of the Diaphragm and Pericardium

The internal thoracic veins receive venous blood from the pericardiophrenic veins, which drain both the diaphragm and the pericardium (the sac surrounding the heart). This function is crucial for maintaining proper circulation in these regions, particularly during respiration and cardiac function. By draining the diaphragm, the internal thoracic veins help regulate blood flow in the muscles involved in breathing. Similarly, draining blood from the pericardium helps support heart function by ensuring the pericardial sac remains well-vascularized.

Contribution to the Thoracic Collateral Circulation

The internal thoracic veins play a role in collateral circulation within the thorax. In cases of obstruction or blockage in other major veins, such as the subclavian vein or the brachiocephalic vein, the internal thoracic veins can serve as an alternative pathway for venous return.^[6] This collateral network ensures that blood can still be returned to the heart even if the primary pathways are compromised, preventing complications such as venous congestion or swelling.

Maintenance of Blood Pressure in the Thoracic and Abdominal Wall

The internal thoracic veins help maintain venous pressure in the thoracic and upper abdominal walls. By providing an efficient route for blood to flow from the chest and abdominal muscles back to the heart, these veins prevent the buildup of venous pressure in the tissues, which could otherwise lead to venous congestion or edema. This regulation of pressure is especially important during activities that increase intrathoracic or intra-abdominal pressure, such as heavy lifting or intense physical exertion.

Connection to the Superior Vena Cava System

The internal thoracic veins are integral to the overall venous return to the superior vena cava. By draining into the brachiocephalic veins, they directly contribute to the venous system that ultimately returns deoxygenated blood to the superior vena cava. This pathway ensures that venous blood from the thoracic wall, diaphragm, and upper abdomen is efficiently transported to the heart for reoxygenation.

Support for Post-Surgical Recovery in the Thoracic Region

In the context of thoracic surgeries, such as procedures involving the ribs, sternum, or chest wall, the internal thoracic veins are important for post-surgical recovery.^[4] By providing proper venous drainage, these veins help prevent the accumulation of blood or fluid in the surgical area, reducing the risk of hematomas or seromas. Their role in ensuring efficient venous return supports tissue healing and reduces post-operative complications.

Prevention of Venous Congestion

The internal thoracic veins are crucial for preventing venous congestion in the chest wall and upper abdomen. If venous drainage were impaired, blood could accumulate in the muscles, skin, and connective tissues, leading to swelling, discomfort, or impaired function of the respiratory muscles. The internal thoracic veins prevent these issues by ensuring a clear and efficient path for venous blood to return to the heart.

Role in Thermoregulation of the Thoracic Wall

By removing deoxygenated blood from the thoracic wall, the internal thoracic veins also contribute to thermoregulation. Blood carries heat, and by draining it from the chest muscles and skin, these veins help dissipate excess heat and maintain a stable temperature in the thoracic region. This function supports overall body temperature regulation, particularly during physical activity or exposure to temperature changes.

Clinical Significance

The internal thoracic veins hold significant clinical importance due to their role in draining the anterior thoracic wall, diaphragm, and upper abdominal wall.^[2] They are often encountered in cardiac and thoracic surgeries, such as coronary artery bypass grafting (CABG), where the internal thoracic artery is frequently used, and care must be taken to avoid damaging the accompanying veins. Damage to the internal thoracic veins during surgery can lead to excessive bleeding or hematoma formation. The internal thoracic veins are also involved in conditions such as venous congestion or obstruction, and their role in collateral circulation makes them critical in compensating for blockages in other major veins like the subclavian or brachiocephalic veins. Additionally, in some cases of thoracic trauma or injury to the chest wall, these veins can be damaged, leading to complications that require careful management. Their anatomy is also important for imaging studies and diagnostic evaluations of the chest.