Posterior Intercostal Arteries (Left)

Description

There are eleven pairs of posterior intercostal arteries that travel within the eleven intercostal spaces.

The first and second posterior intercostal arteries differ from the other posterior intercostal arteries, since they arise from the supreme intercostal artery, a branch of the costocervical artery. The remaining intercostal arteries arise from the posterolateral descending thoracic aorta. The right posterior intercostal arteries are longer than their left counterparts (since the descending thoracic aorta sits to the left of the midline); thus the right posterior intercostal arteries must travel over the vertebral bodies. When it reaches the intercostal space, the posterior intercostal artery is situated, firstly, between the pleura of the lungs and the internal intercostal membranes and muscle, then between the innermost and internal intercostal muscles.

The posterior intercostal artery extends anteriorly, lying within the costal groove of the rib above and accompanied by a vein superiorly and a nerve inferiorly (i.e., the posterior intercostal vein and anterior ramus of thoracic nerve). It continues to travel in the intercostal space and anastomoses with the anterior intercostal branches of the internal thoracic artery. Along its path, the posterior intercostal arteries give off dorsal, collateral, and lateral cutaneous branches, which are responsibly for supplying structures of the thoracic wall.