Fourth Posterior Intercostal Artery

Origin

The first and second posterior intercostal arteries arise from the supreme intercostal artery, a branch of the costocervical trunk. The third to eleventh posterior intercostal arteries arise from the posterolateral aspect of the descending thoracic aorta.

Course

From their origin, the posterior intercostal arteries travel posterolaterally along the posterior thoracic wall to reach its corresponding intercostal space. 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 of 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.

Additionally, the third intercostal artery forms an anastomosis with the supreme intercostal artery (not depicted in the model), thus, may provide the major supply to the second intercostal space.

Branches

Along its path, the posterior intercostal arteries give off dorsal, collateral, and lateral cutaneous branches.

Supplied Structures

The posterior intercostal arteries supply structures of the thoracic wall.