Internal thoracic artery

The internal thoracic artery (previously known as internal mammary artery) arises from the subclavian artery near its origin.

It travels downward on the inside of the ribcage, approximately a centimeter 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 costal cartilages and internal intercostal muscles, but superficial to the transversus thoracis muscle.

It continues downward until it divides into its terminal branches around the sixth costal cartilage (see below).

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

• Superior epigastric artery — continues the course of the internal thoracic artery, travelling downward into the abdominal wall