Posterior communicating artery

At a glance

English

Posterior communicating artery

Latin (TA2)

Arteria communicans posterior

System

Artery

Region

Head

Side

Paired, left and right

About the posterior communicating artery

The posterior communicating artery is a small connecting vessel that forms the side of the arterial circle on the underside of the brain. There is one on each side. It arises from the back of the internal carotid artery shortly before the carotid splits into the anterior and middle cerebral arteries, and runs backwards and slightly medially to join the posterior cerebral artery a short distance from the basilar bifurcation. So on each side it ties the three cerebral arteries of that half into one system.

Along its course it lies above the oculomotor nerve, which emerges between the posterior cerebral and superior cerebellar arteries, and beside the optic tract, the tuber cinereum and the mammillary bodies. It gives small perforating branches that pass through the posterior perforated substance to the medial thalamus, the hypothalamus and the internal capsule.

Its importance is as a bridge between the carotid supply in front and the vertebrobasilar supply behind. If one system is narrowed or blocked, blood can flow through this artery in either direction to support the other, although its size varies widely, and it may be thread-like or absent on one side. Its development explains this. In the embryo the posterior cerebral artery grows mostly out of the communicating vessel; later the basilar artery takes over in most people. In about a fifth of adults the communicating artery remains large and is the main source of the posterior cerebral artery, the fetal pattern, so that the occipital lobe on that side depends on the internal carotid.

Aneurysms at the junction of the posterior communicating and internal carotid arteries are among the commonest in the circle of Willis, after those of the anterior communicating artery. Because the oculomotor nerve runs right beside this junction, an enlarging aneurysm can press on it, giving a drooping lid, an outward-turned eye and, typically, a dilated pupil; a new painful third-nerve palsy of this kind is treated as an emergency.

Course and supply

Arises from

The posterior wall of the internal carotid artery, just before its terminal division.

Ends in

Joins the posterior cerebral artery near the basilar bifurcation.

Supplies

Connects the carotid and vertebrobasilar systems, providing collateral flow, and sends perforating branches to the thalamus, hypothalamus and internal capsule.