The Anatomy of the Posterior Communicating Artery (PCOM)

Part of the Circle of Willis Supplying Blood to the Brain

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The posterior communicating artery (PCOM) is a part of a group of arteries in the brain known as the circle of Willis. The artery connects the internal carotid and the posterior cerebral arteries. Its role is to provide blood supply to the brain. The posterior communicating artery is a location where aneurysms can potentially occur. 

Diagram of the brain, showing the circle of Willis / Getty Images


The circle of Willis is a band of arteries at the base of the brain that connects the major arterial systems to the brain. As part of the lower half of the circle of Willis, the posterior communicating artery starts from the internal carotid artery (ICA) and joins the internal carotid and the posterior cerebral arteries (PCA).

The PCOM is located in the back of the head at the back end of the circle of Willis. It is located on the left and right sides of the head and is relatively short.

The posterior cerebral arteries branch off from the basilar artery. The left and right PCAs form the longest sections of the circle of Willis. The internal carotid arteries are located in the front of the neck. They travel through the carotid canal, where they enter the skull.

An anatomical variation called the fetal posterior communicating artery occurs when the posterior communicating artery is significantly larger than the posterior cerebral artery. When this happens, the posterior communicating artery becomes the main pathway instead of the basilar artery.


Arteries are blood vessels that transport oxygen and blood to the cells in the body. The posterior communicating artery supplies blood and oxygen to the brain in instances where the internal carotid or posterior cerebral arteries are blocked.

The posterior cerebral arteries provide blood to the occipital and temporal lobes, midbrain, thalamus, and choroid plexus. The internal carotid supplies the head and brain with blood.

In the circle of Willis, the anterior arteries supply blood and oxygen to the front of the brain, and the posterior arteries are responsible for supplying blood and oxygen to the back of the brain. 

Clinical Significance

Conditions affecting the PCOM can have a major impact on the brain.


The posterior communicating artery is a potential location of aneurysms. An aneurysm is a bulging area in an artery. Although aneurysms in the circle of Willis most commonly occur in the anterior communicating artery, those in the posterior circulation account for 15% to 20% of all intracranial aneurysms.

PCOM aneurysms are more likely to rupture than those that occur elsewhere in the brain. Aneurysms are classified by size and shape, with saccular aneurysms being the most common. Saccular aneurysms are those that bulge out from the artery like a berry attached by a stalk.

Symptoms do not always occur with aneurysms, especially if they haven’t ruptured. When they do occur, symptoms include headaches, stroke symptoms, seizures, vision changes, and loss of consciousness. Brain aneurysms generally develop without a known cause, but genetics may play a role.

Aneurysms are not always fatal, but they can be deadly, especially if they rupture. Diagnosis is done via computerized tomography (CT scan), magnetic resonance imaging (MRI), and cerebral angiography. Treatment is coordinated by a neurologist or a neurosurgeon.

Sometimes, unruptured aneurysms do not require treatment. Other times, they may need to be surgically repaired. Lifestyle changes may be suggested to reduce the risk of a rupture. Avoiding activities that may involve a risk of hitting your head or increasing your blood pressure may be some things that your healthcare provider advises. 


A stroke occurs when there is an interruption of blood flow in an artery. This blockage keeps blood from reaching its destination in the brain, resulting in a loss of function in the affected region.

Strokes can happen when a blood clot gets lodged in an artery, becomes blocked from disease, or if a blood vessel bleeds. Spotting a stroke as it happens is important so that a person can receive treatment and can have a better chance of rehabilitation. 

Healthcare providers have developed the acronym FAST to make it easier to remember the signs to watch for:

  • Facial drooping
  • Arm weakness
  • Speech difficulties
  • Time to call 9-1-1

At-home diagnosis can be extremely useful in determining if someone is having a stroke. Studies have shown that the Cincinnati Prehospital Stroke Scale is an accurate prehospital screening tool. In the hospital, healthcare providers may use EKG or ECG, spinal tap, blood tests, CT scan, MRI, and cerebral angiography to diagnose a stroke.

Treatment for stroke usually involves blood thinners, heparin, and aspirin. Managing blood pressure, blood glucose, fluids, and electrolytes are also important. Surgery is not a common treatment for strokes but may be recommended in some circumstances.

Traumatic Brain Injury

Head trauma can damage the PCOM. Traumatic brain injuries (TBI) that damage the PCOM can occur from falls, blows to the head, accidents, and sports injuries. 

Symptoms of a TBI can vary, but might include headache, dizziness, balance problems, confusion, and loss of consciousness. TBIs are usually diagnosed by a CT scan or MRI. Treatment may include medication or surgery to temporarily remove part of the skull to accommodate swelling. 

5 Sources
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By Kathi Valeii
As a freelance writer, Kathi has experience writing both reported features and essays for national publications on the topics of healthcare, advocacy, and education. The bulk of her work centers on parenting, education, health, and social justice.