Perforating branches of internal thoracic artery

The perforating branches of the internal thoracic artery (also known as internal mammary artery perforators, or IMAPs) are cutaneous vessels that arise from the internal thoracic artery (ITA) as it descends along the posterior surface of the anterior chest wall, approximately 1 cm lateral to the sternal border. These branches pass anteriorly through the intercostal muscles and the medial fibers of the pectoralis major muscle to reach and supply the overlying skin of the ventromedial thorax in a segmental fashion.

Anatomical characteristics:

• The perforating branches are given off by the ITA in the first through sixth intercostal spaces. Each perforator pedicle typically consists of one artery and one vein, accompanied by the anterior cutaneous branch of the corresponding intercostal nerve.

• The second intercostal space most commonly harbors the dominant perforator, which is the largest in both sexes, with a mean diameter of approximately 0.8-1.0 mm at its point of emergence. The accompanying vein measures approximately 1.53.2 mm in diameter.

• A single dominant perforator (at least twice the size of any other) is present in approximately 85% of cases, while codominance (two perforators of equal size) occurs in about 15%.

• The mean distance from the sternal border to the point of ramification from the ITA is approximately 6.7-7.0 mm, and the mean intramuscular pedicle length (from the ITA to the subcutaneous tissue) is approximately 17 mm.

• In women, perforators from the third and fourth intercostal spaces also tend to be large, as they contribute significantly to the arterial supply of the breast, providing up to 60% of total breast blood flow.

Branching patterns:

The ITA gives off four types of proper (solitary) branches sternal, perforating, intercostal, and mediastinal as well as common trunks that combine destinations. Relevant combined patterns include the sterno-perforating branch, which supplies the sternum before perforating anteriorly to supply the pectoral region and anastomose with the thoracoacromial artery. The mean external diameter of proper branches is 0.72 mm, while common trunks average 1.06 mm with a mean length of 3.0 mm.

Clinical significance:

The perforating branches are clinically important in several contexts. They serve as recipient vessels for microsurgical free-tissue breast reconstruction (e.g., DIEP flap), offering advantages including good caliber match with the deep inferior epigastric vessels, more medial flap positioning for better aesthetics, and avoidance of rib cartilage resection when used instead of the main ITA trunk. They also form the vascular basis of the internal mammary artery perforator (IMAP) flap, used for reconstruction of the anterior chest, breast, and head and neck defects. Additionally, understanding the branching pattern is critical during ITA harvesting for coronary artery bypass grafting, as branches should be ligated close to the ITA trunk to preserve collateral blood supply to the sternum via sterno-perforating and sterno-intercostal common trunks.