Posterior communicating artery

Origin and course

The posterior communicating artery originates from the intracranial portion of the internal carotid artery, specifically from its C7 segment. The left and right posterior communicating arteries usually differ in size, with one of them being notably larger than the other. The artery takes a short posterior course, passing above the oculomotor nerve (CN III) and anastomoses with the posterior cerebral artery in the interpeduncular fossa.

Given that the posterior cerebral artery is the terminal branch of the basilar artery, the posterior communicating artery is an anastomotic channel between the anterior cerebral circulation (internal carotid artery) and the posterior cerebral circulation (basilar artery).

Branches and supply

The main function of the posterior communicating artery relates to its role to connect the anterior and posterior cerebral circulations. In case when either basilar or internal carotid arteries are occluded, the posterior communicating artery provides the brain with a viable blood supply by conducting the blood from the unoccluded vessel.

The fact that one of the PComm arteries is usually larger than the other one plays an important role in these situations; the smaller artery is unfit to bear the amount of blood that is necessary to compensate for the occlusion. However, the larger PComm artery is competent for such a role and it is a dominant anastomotic channel in the situations of this kind.

Besides its anastomotic function, the posterior communicating artery actively participates in the blood supply of the deep structures of the brain. The posterior communicating artery gives off a series of 4-14 small perforating branches called the posteromedial central arteries. These branches penetrate the posterior perforated substance and supply the posterior limb of the internal capsule, medial portion of the thalamus, central part of the hypothalamus, subthalamus, mammillary bodies, optic chiasm and lateral wall of the third ventricle.

The number of perforating arteries varies among individuals, but the most consistent ones are named according to the structures that they supply; mammillary branches, hypothalamic branch, thalamotuberal artery, artery of tuber cinereum and the chiasmatic branch. Note that the vascular territory of the PComm is aided by the posterolateral central branches of the posterior cerebral artery. So, in case of the smaller number of the PComm perforators, the branches of the posterior cerebral artery provide the blood supply for the above-mentioned regions.

Anatomical variations

In about 20% of individuals, the posterior communicating artery is notably larger than the posterior cerebral artery. In this case, the PComm is the main source for the posterior cerebral artery instead of the basilar artery. This variant is called the fetal posterior communicating artery.