Mediastinal branches of internal thoracic artery

The mediastinal branches of the internal thoracic artery (ITA) are small, variable vessels that arise from the posterior (deep) aspect of the ITA and course medially into the anterior mediastinum. They are classified as one of the four types of "proper" (solitary) branches of the ITA alongside sternal, perforating, and anterior intercostal branches. These small arteries supply the anterior mediastinal contents, including mediastinal connective tissue, the thymus (or its remnant), mediastinal lymph nodes, and the posterior surface of the sternum.

Origin and course

The ITA itself arises from the inferolateral aspect of the first part of the subclavian artery, descends approximately 1 cm lateral to the sternal border between the internal intercostal muscles and the transversus thoracis muscle, and terminates most commonly at the sixth intercostal space by bifurcating into the musculophrenic and superior epigastric arteries. Along its course, it gives off parietal and visceral branches. The mediastinal branches are among the visceral branches, arising from the medial or posterior surface of the ITA and directed into the mediastinal space.

Anatomical characteristics

A detailed cadaveric study by Pietrasik et al. classified all ITA branches into proper (solitary) branches and common trunks. The proper branches sternal, perforating, intercostal, and mediastinal had a mean external diameter of approximately 0.72 mm. The mediastinal branches are typically the smallest and most variable of the ITA's collateral branches. They are distinct from the larger named visceral branch, the pericardiacophrenic artery, which arises from the ITA in approximately 89-99% of cases and accompanies the phrenic nerve to supply the pericardium and diaphragm.

Structures supplied

The mediastinal branches provide blood supply to:

• Thymic tissue (or thymic remnant in adults)

• Anterior mediastinal fat and connective tissue

• Mediastinal lymph nodes

• Pericardium (in part, supplementing the pericardiacophrenic artery)

• Bronchial tissue (minor contributions)

Clinical significance

These branches are of particular importance during ITA harvesting for coronary artery bypass grafting (CABG). The ITA is the conduit of choice for revascularization of the left anterior descending artery due to its superior long-term patency. During skeletonized or pedicled ITA dissection, the mediastinal branches along with sternal, intercostal, and perforating branches must be carefully identified and ligated. Ligation should be performed as close to the ITA trunk as possible to preserve collateral circulation, especially to the sternum, which is critical for sternal healing after median sternotomy.