Internal thoracic artery

Structure

The internal thoracic artery arises from the anterior surface of the subclavian artery near its origin. It has a width of between 1–2 mm.

It travels downward on the inside of the rib cage, approximately 1 cm from the sides of the sternum, and thus medial to the nipple. It is accompanied by the internal thoracic vein.

It runs deep to the abdominal external oblique muscle, but superficial to the vagus nerve.

In adults, the internal thoracic artery lies closest to the sternum at the first intercostal space. The gap between the artery and lateral border of the sternum increases when going downwards, up to 1.1 cm to 1.3 cm at the sixth intercostal space. In children, the gap ranges from 0.5 cm to 1.0 cm.

Branches

• Mediastinal branches
• Thymic branches
• Pericardiacophrenic artery – travels with the phrenic nerve
• Sternal branches
• Perforating branches
• Twelve anterior intercostal branches, two to each of the top six intercostal spaces. In a given space, the upper branch travels laterally along the bottom of the rib until it anastomoses with its corresponding posterior intercostal artery. The lower branch of the space anastomoses with a collateral branch of the posterior intercostal artery.

After passing the sixth intercostal space, the internal thoracic artery splits into the following two terminal branches:

• Musculophrenic artery – roughly follows the costal margin and it again gives branch for 7,8,9 ribs
• Superior epigastric artery – continues the course of the internal thoracic artery, travelling downward into the abdominal wall and to the content of rectus sheath