Posterior intercostal arteries
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The intercostal spaces are supplied by pairs of anterior and posterior intercostal arteries. The posterior intercostal arteries arise from the aorta and in part supply the spine and spinal cord and thus are considered segmental arteries.
There are 11 paired arteries that constitute the posterior intercostal arteries. The first two intercostal spaces are supplied by the superior intercostal artery, and the remaining nine are supplied by separate branches from the descending thoracic aorta 1. The right sided arteries are longer as the aorta lies to the left of the midline. They pass in front of the vertebrae and behind the azygos venous system, esophagus and thoracic duct. The left sided arteries run posteriorly adjacent to the vertebrae and enter into the intercostal space.
The superior intercostal artery is the descending branch of the costocervical trunk, which arises from the second part of the subclavian artery 2. It enters the thorax anterior to the neck of the first rib with the sympathetic trunk on its medial side.
The posterior intercostal artery divides into the anterior and posterior rami.
The anterior ramus runs along the costal groove, accompanied by an intercostal nerve and vein. The vein lies superior to the artery and the nerve inferior to it (mnemonic "VAN"). The intercostal artery, vein and nerve courses deep to the internal and superficial to the innermost intercostal muscles. The anterior ramus divides into four branches 1:
The posterior ramus (dorsal branch) gives off three branches:
The spinal branch gives off radicular, segmental medullary, and/or radiculomedullary branches.
Along with the anterior intercostal arteries, the posterior intercostal arteries supply the muscles and skin within the intercostal spaces as well as the parietal pleura 3.
Branches of the spinal branch anastomose with other vessels to supply the nerve roots and/or spinal cord (via the anterior and posterior spinal arteries).
The musculocutaneous branches supply the paraspinal soft tissue structures of the back.