First posterior intercostal artery

At a glance

English

First posterior intercostal artery

Latin (TA2)

Arteria intercostalis posterior prima

System

Artery

Region

Trunk

Side

Paired, left and right

About the first posterior intercostal artery

Most posterior intercostal arteries come straight from the back of the descending thoracic aorta. The aorta, however, begins too low to reach the highest spaces easily, so the first two spaces are served from the subclavian system instead. The first posterior intercostal artery is a branch of the supreme (superior) intercostal artery, which itself comes from the costocervical trunk.

The supreme intercostal artery drops behind the pleura across the neck of the first rib. Here it lies between the sympathetic trunk on its medial side and the ventral ramus of the first thoracic nerve on its lateral side. As it passes, it gives the first posterior intercostal artery, which turns laterally into the first intercostal space beneath the first rib.

In the space the vessel follows the general intercostal plan. It runs forwards with its companion vein and nerve, sending a dorsal branch back to the muscles and skin of the upper back and a branch into the vertebral canal, before supplying the intercostal muscles and the overlying chest wall. Towards the front it meets the anterior intercostal branch of the internal thoracic artery, so the space is fed from both ends.

Because it arises from the subclavian side rather than from the aorta, the vessel does not carry the collateral flow of coarctation of the aorta, in which the lower intercostal arteries fill backwards from the internal thoracic artery to reach the aorta below the narrowing; this is why the first two ribs are spared the notching seen on lower ribs. Its position at the neck of the first rib places it close to the stellate ganglion and the lower roots of the brachial plexus.

Course and supply

Arises from

The supreme intercostal artery, a branch of the costocervical trunk of the subclavian artery, as it crosses the neck of the first rib.

Ends in

Runs forwards in the first intercostal space and ends by anastomosing with the anterior intercostal branch of the internal thoracic artery.

Supplies

Supplies the first intercostal space, its muscles and the adjacent chest wall, with dorsal branches to the upper back and a spinal branch to the vertebral canal.