Posterior intercostal arteries originate as:
- The 1st and 2nd posterior intercostal arteries are the divisions of superior intercostal artery which is a branch of the costocervical trunk.
- The 3rd – 11th posterior intercostal arteries emerge straight from the descending thoracic aorta.
Posterior intercostal arteries emerge from vessels that are connected with the posterior thoracic wall. The supreme intercostal artery, which moves down within the thorax as a division of the costocervical trunk in the neck creates the upper two posterior intercostal arteries on both sides. The costocervical trunk is a posterior branch of the subclavian artery.
Due to the location of the descending aorta on the left part of the front of the vertebral column, the right posterior intercostal arteries are lengthier compared to the left. In front of the anterior part of vertebral body, they travel behind the esophagus, thoracic duct, azygos vein, and sympathetic chain. The left posterior intercostal arteries go towards the back of the hemiazygos vein as well as sympathetic chain in front of the side of the vertebral body and are smaller in length. The posterior intercostal artery is located amongst the intercostal vein above as well as the intercostal nerve below within the intercostal space. The neurovascular bundle in the intercostal space is located in the middle of the internal intercostal and intercostalis intimus muscles.
- Dorsal branch supplies the spinal cord, vertebra and muscles, and skin of the back.
- Collateral branch emerges near the angle of the rib, then travels forwards alongside the upper margin of the rib below and terminates by anastomosing along with the lower anterior intercostal artery.
- Muscular branches supply the intercostal, pectoral, and serratus anterior muscles.
- Lateral cutaneous branch directly goes along the lateral cutaneous branch of the intercostal nerve.
- Mammary branches (external mammary arteries) emerge from posterior intercostals arteries of the 2nd, 3rd, and 4th intercostal spaces and supply the mammary gland of breasts.
- Right bronchial artery arises from right 3rd posterior intercostal artery.
The posterior intercostal artery splits within the anterior and posterior rami. The anterior ramus travels beside the costal groove, alongside an intercostal nerve and vein. The posterior ramus produces branches which anastomose together with other vessels in order to supply the spinal cord and soft tissue structures of the back.