Posterior Intercostal Arteries

The posterior intercostal arteries are a set of paired arteries that supply the intercostal spaces, back muscles, vertebrae, spinal cord, and overlying skin. They originate from the thoracic aorta and play a key role in vascularizing the thoracic wall. Each artery runs within an intercostal space alongside an intercostal vein and nerve, forming the neurovascular bundle of that space.

Origin

There are typically 11 pairs of posterior intercostal arteries, corresponding to the 11 intercostal spaces. Their origin varies as follows:

• First and second intercostal spaces: Supplied by the superior intercostal artery, a branch of the costocervical trunk (from the subclavian artery)

• 3rd to 11th intercostal spaces: Arise directly from the posterior surface of the descending thoracic aorta

Course

Each posterior intercostal artery travels laterally from its origin and enters the intercostal space. It courses between the internal intercostal and innermost intercostal muscles, within the costal groove of the rib, along with the corresponding intercostal vein and nerve. The typical arrangement from superior to inferior is: vein, artery, nerve (VAN).

Before entering the intercostal space, the artery gives off several branches.

Dorsal Branch

• Arises near the vertebral column

• Passes posteriorly to supply the vertebral muscles, spinal cord, meninges, and skin of the back

Lateral Cutaneous Branch

• Perforates the intercostal and superficial muscles

• Supplies the lateral thoracic wall and skin

Terminal Branches

• End as anterior and posterior terminal branches within the intercostal muscles

Collateral Circulation and Anastomoses

The posterior intercostal arteries anastomose with the anterior intercostal arteries, which arise from the internal thoracic artery (superiorly) and musculophrenic artery (inferiorly). These anastomoses ensure a continuous blood supply to the thoracic wall and play a key role in collateral circulation during arterial blockage.

Structures Supplied

• Intercostal muscles (external, internal, innermost)

• Overlying thoracic skin and subcutaneous tissue

• Parietal pleura

• Thoracic vertebrae and spinal meninges

• Spinal cord and dorsal root ganglia (via spinal branches)

• Back muscles and skin (via dorsal branches)

Venous Drainage

Each posterior intercostal artery is accompanied by a posterior intercostal vein, which drains into:

• Right side: Azygos vein

• Left side: Hemiazygos or accessory hemiazygos veins

Topographic Relationships

• Superior: Intercostal vein

• Inferior: Intercostal nerve

• Anteriorly: Intercostal muscles and ribs

• Posteriorly: Vertebral bodies and paravertebral muscles

Histological Structure

Posterior intercostal arteries are medium-sized muscular arteries, with a tunica media rich in smooth muscle and elastic fibers to accommodate thoracic movement and maintain arterial pressure.

Clinical Significance

• Thoracentesis: To avoid damaging the artery, procedures are typically performed just above the upper border of the lower rib in an intercostal space

• Coarctation of the Aorta: Enlarged posterior intercostal arteries may serve as collateral pathways and become visible on imaging as “rib notching”

Topographic Summary

• Total pairs: 11 (first two from subclavian system, rest from thoracic aorta)

• Course: Runs in the costal groove between internal and innermost intercostal muscles

• Accompanied by: Intercostal vein (superior) and nerve (inferior)

• Anastomoses: With anterior intercostal arteries

• Drainage: Into azygos system