The posterior intercostal arteries (also known as the aortic intercostals) arise from the descending thoracic aorta to supply intercostal spaces.
The posterior intercostal arteries arise from the back of the thoracic aorta. On the right side, these arteries are longer because the aorta lies to the left of the midline. They travel in front of the vertebrae and behind vessels of the azygos venous system, esophagus, and thoracic duct. The left-sided posterior intercostal arteries pass posteriorly adjacent to the vertebrae and enter the intercostal spaces. The aortic intercostals supply the lower nine intercostal spaces.
The first two intercostal spaces are supplied by branches of the supreme intercostal artery (and these branches are sometimes also referred to as posterior intercostal arteries). The supreme intercostal artery is a branch of the costocervical trunk, which arises from the subclavian artery.
Each posterior intercostal artery divides into anterior and posterior branches.
The anterior branch passes along the costal groove (found on the internal surface of ribs). Within the groove, it is accompanied by an intercostal nerve and vein. It then splits into four branches:
The posterior branch of the posterior intercostal artery gives rise to branches that anastomose with other vessels to supply the spinal cord, as well as soft tissue structures of the back.
Along with the anterior intercostal arteries, which arise from the internal thoracic artery, the posterior intercostal arteries supply the muscles and other components filling the intercostal spaces, as well as the parietal pleura.