Posterior intercostal arteries

The posterior intercostal arteries are paired segmental vessels that supply the thoracic wall, spinal structures, and associated musculature. They play an essential role in perfusing the intercostal spaces and contribute significantly to collateral circulation within the thorax.

Origin: The first two posterior intercostal arteries arise from the supreme intercostal artery, a branch of the costocervical trunk of the subclavian artery. The next nine pairs (from the 3rd to the 11th intercostal spaces) originate directly from the descending thoracic aorta. The 12th pair forms the subcostal arteries, which are usually described separately.

Course: The posterior intercostal arteries run laterally within the costal groove along the inferior border of each rib. They course between the internal intercostal and innermost intercostal muscles, accompanied by the intercostal vein and nerve, forming the typical neurovascular bundle (VAN).

Along their course, they give rise to several branches:

• Dorsal branch, supplying the vertebrae, deep muscles of the back, and overlying skin.

• Collateral branch, which runs along the superior border of the rib below.

• Lateral cutaneous branch, supplying the skin of the thoracic wall and the breast.

They anastomose anteriorly with the anterior intercostal arteries, which arise from the internal thoracic and musculophrenic arteries.

Branches and distribution: Posterior intercostal arteries provide muscular branches to the intercostal muscles, pectoral muscles, serratus anterior, and abdominal wall muscles. Cutaneous branches supply the skin of the thoracic wall and the breast. Spinal branches pass through the intervertebral foramina to supply the vertebrae, spinal cord, nerve roots, and meninges (radicular branches).

Clinical note: These arteries are important contributors to collateral circulation, particularly in conditions such as coarctation of the aorta. They may also become enlarged during lactation due to increased vascular demand of the breast.