Internal thoracic artery

The internal thoracic artery (previously called the internal mammary artery) supplies the anterior body wall and its associated structures from the clavicles to the umbilicus. 

Gross anatomy

Origin

The internal thoracic artery arises from the first part of the subclavian artery in the base of the neck.

Course

It then passes from the neck to the thorax posterior to the subclavian vein and first rib. It has a vertical course and runs inferiorly within a few centimetres laterally of the sternum in a neurovascular plane between the transversus thoracus muscle posteriorly and the costal cartilages and internal intercostal muscles anteriorly. At the sixth-to-seventh costal cartilages the internal thoracic artery bifurcates into two terminal branches - musculophrenic artery and superior epigastric artery. 

Along its course, the internal thoracic artery gives off perforating branches which pass superficially towards the skin. At the second-to-fourth intercostal spaces these perforating branches are larger (and become even more enlarged during pregnancy) to supply to the breasts. 

The internal thoracic artery, via its superior epigastric branches anastomoses with the inferior epigastric arteries, provides an important alternate blood supply if the aorta becomes occluded between the arch of the aorta and descending aorta (see: coarctation of the aorta).

Branches

• anterior intercostal arteries within each intercostal space
• pericardiophrenic artery (runs with the phrenic nerve)
• perforating cutaneous branches
• musculophrenic artery (terminal branch)
• superior epigastric artery (terminal branch)

Supply

The internal thoracic artery supplies the anterior body wall from clavicle to umbilicus including the sternum and the breasts. In addition, via the pericardiophrenic artery it supplies the mediastinum, thymus, phrenic nerves and pericardium.

Variant anatomy

Recognition of variation of origin of the internal thoracic artery is important because it is often used as a coronary artery bypass graft:

• anomalous origin in 20% ⁴
  • second part (uncommon; ~7%) and third part (rare; ~1%) of subclavian artery ³
  • common origin with thyrocervical trunk ⁴
  • other subclavian artery branches (e.g. subscapular or transverse cervical arteries) ⁴
• terminal trifurcation (~12.5%) with an additional xiphoid branch