Internal thoracic artery
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The internal thoracic artery arises from the first part of the subclavian artery in the base of the neck.
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 centimeters laterally of the sternum in a neurovascular plane between the transversus thoracis 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 -
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).
musculophrenic artery (terminal branch)
superior epigastric artery (terminal branch)
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.
Recognition of variation of origin of the internal thoracic artery is important because it is often used as a coronary artery bypass graft: