In the brain, oxygenated blood travels through an extensive and central cerebral arterial circle. This network is called the circle of Willis. The posterior communicating artery makes up a large part of the circle's lower half.
The circle is symmetrical, so there are two posterior communicating arteries, with each having a left or right designation. Both are bridges between larger blood vessels, connecting the middle cerebral artery with the posterior cerebral artery. Eventually, this joins the basilar artery, which splits into two vertebral arteries.
Since the cerebral arterial circle is so central in the brain, problems with it may have life-threatening consequences. The posterior communicating artery is one of the potential sites of aneurysms, which are diseased areas of an artery that are weak and bulging (sometimes resulting in rupture). Most aneurysms occur in the anterior communicating artery, but in terms of frequency, the posterior comes in second. Such an aneurysm may ultimately lead to paralysis (“palsy”) of the oculomotor nerve. This nerve controls various functions of the eye, including movement of the eye, focus, and positioning of the upper eyelid. Palsy of this nerve can affect any of the various functions it controls.
The posterior communicating artery develops late during fetal gestation (development that occurs while a baby is still in the womb) as embryonic vessels begin to fuse together. However, this does not lead to any frequently occurring congenital (birth) defects.