Basilar artery

Author: Lorenzo Crumbie, MBBS, BSc • Reviewer: Dimitrios Mytilinaios, MD, PhD
Last reviewed: October 30, 2023
Reading time: 13 minutes

The basilar artery is a relatively large, robust blood vessel located in the posterior cranial fossa. It is the main blood vessel that forms the posterior circulation of the brain.

This is one of two arterial circuits (the other being the anterior circulation) that delivers up to 15% of the total cardiac output to the brain tissue. This high demand for oxygenated blood is based on the diverse physiological functions that the brain executes on a daily basis. An occlusion of the basilar artery can have debilitating implications, such as speech difficulties, visual disturbances, cranial nerve palsies and altered consciousness.

Key facts about the basilar artery
Origin	Union of the vertebral arteries at the pontomedullary junction
Course	Along the basilar groove on the ventral surface of the pons in the pontine cistern
Termination	Bifurcates into the paired posterior cerebral arteries
Branches	Anterior inferior cerebellar artery Internal auditory (labyrinthine)artery Superior cerebellar artery

This article will review the gross anatomy and development of the basilar artery, including the course of its branches. Clinical information regarding lesions of the basilar artery will also be included.

Contents

Branches
Circle of Willis
Development
Clinical significance
1. Stroke (cerebrovascular accident)
Sources

+ Show all

Branches

The basilar artery is a large vessel that ascends along the ventral surface of the pons. It originates in the midline at the pontomedullary junction from the union of the vertebral arteries. The vessel then travels in a relatively shallow groove on the pons known as the basilar groove, within the pontine cistern. The lower half of the bony clivus is ventral to the basilar artery. Consequently, it is referred to as the basilar part of the occipital bone.

Along its course, the basilar artery gives off five major branches. These are:

anterior inferior cerebellar,
internal auditory (labyrinthine),
superior cerebellar,
pontine and
posteromedial arteries.

The vessel terminates at a bifurcation where it gives off the paired posterior cerebral arteries that contribute to the circle of Willis.

Anterior inferior cerebellar artery (AICA)

The anterior inferior cerebellar artery that arises from the proximal part of the basilar artery is one of the 3 pairs of arteries that supply the cerebellum. It is ventrally related to the abducens (CN VI), facial (CN VII), and vestibulocochlear (CN VIII) nerves. The vessel takes a posterolateral course as it goes to supply the inferior aspect of the cerebellum. It also anastomoses with the posterior inferior cerebellar artery – a branch of the vertebral artery.

The territory of the cerebellum covered by the anterior inferior cerebellar artery is dependent on the dominance of the posterior inferior cerebellar artery (a branch of the vertebral artery). However, the vessel supplies the anteroinferior surface and flocculus of the cerebellum, middle cerebellar peduncle, and the inferolateral part of the pons. On occasion, the vessels may also reach as far as the proximal medulla oblongata to supply this part of the brainstem.

Superior cerebellar artery

Before the basilar artery divides into its terminal branches, it gives off the superior cerebellar artery. This vessel emerges in a lateral direction, caudal to the oculomotor (CN III) nerve. It courses around the cerebral peduncles (pedunculi cerebri) and passes below the trochlear (CN IV) nerve. It eventually gains access to the superior aspect of the cerebellum, which it supplies, along with the tela choroidea of the 3rd ventricle, the pineal body, pons, and superior medullary velum. It also forms an anastomosis with derivatives of the inferior cerebellar arteries.

The function of the superior cerebellar artery is to supply the superior surface of the cerebellum. It also gives unnamed branches to other nearby areas. These include:

Pons
Superior medullary velum
Pineal body
Tela choroidea of the third ventricle.

Smaller Branches

Occasionally, a slender internal auditory (labyrinthine) artery arises from the basilar artery. In some instances, this vessel also originates from the superior cerebellar, posterior inferior cerebellar, or anterior inferior cerebellar arteries. Along with CN VII and CN VIII, the artery traverses the internal acoustic meatus to supply the internal ear.

The basilar artery also gives off numerous pontine arteries from its lateral surface (bilaterally) as well as posteromedial (paramedian) arteries from the distal bifurcation. These vessels enter the pons to provide arterial supply.

Posterior cerebral arteries

The basilar artery bifurcates behind the dorsum sellae to form the two posterior cerebral arteries. They travel superior to the smaller superior cerebellar artery and are separated from that artery by CN III. The arteries continue in a course lateral to the midbrain (adjacent to CN IV).

Along their course, they join with the posterior communicating artery to complete the circle of Willis. Subsequently, they course around the pedunculi cerebri toward the tentorial aspect of the cerebrum. Here, they give small terminal branches that supply the occipital and temporal lobes.

Circle of Willis

There is a major communication between the dual supply to the brain. The anterior communicating artery provides communication between the contralateral anterior cerebral arteries. The posterior communicating artery bridges each ipsilateral internal carotid artery with the posterior cerebral artery.

Circle of Willis: Diagram

The completed structure is known as the circle of Willis. It surrounds the optic chiasm and infundibulum, as it rests within the chiasmatic and interpeduncular cisterns. The circular anastomosis was initially believed to provide an alternative route for blood flow in the event of vascular occlusion. While that theory still stands, there are additional concepts that suggest the vascular bed may also serve as a pressure relief system to accommodate increased blood flow in instances of raised intracranial pressure.

Take a look at the following resources to cement your knowledge about the basilar artery and nearby arteries of the brain.

Development

The formation of the basilar artery is initiated by the growing brainstem and occipital lobe. Tributaries arising from the internal carotid artery and vertebral arteries all contribute to the formation of the basilar artery.

Worried about remembering all the arteries of the Circle of Willis? Ease into the topic, practice identifying them and test yourself by using our specially designed Circle of Willis quizzes and unlabeled diagrams!

During the 4th gestational week, the internal carotid artery bifurcates into the anterior and posterior divisions. It is the posterior division that gives rise to the fetal posterior cerebral artery, which eventually feeds the basilar artery. Also developing during the 3rd to 4th gestational week are the carotid-vertebrobasilar anastomoses. In the 5th gestational week, these vessels go on to form the distal portion of the trunk of the basilar artery.

The paired vertebral arteries develop during the 5th gestational week. They converge in the midline at the pontomedullary junction, where they form the proximal part of the basilar artery.

Clinical significance

Hypoperfusion of any organ results in a decrease in oxygen and nutrient supply to these tissues. Consequently, if the tissues remain hypoperfused for a prolonged period, they will die. This process is known as infarction, and the resulting lesion is referred to as an area of infarct. In the brain, infarcted tissue undergoes liquefactive necrosis, as the tissue is digested by enzymes released during tissue damage.

Anything that causes disruption of blood flow through the basilar artery can result in hypoperfusion of the areas which it supplies. Aneurysms, blood clots, and other lesions of the basilar artery are just a few examples

Stroke (cerebrovascular accident)

Clinically, the prolonged hypoperfusion manifests as a cerebrovascular accident (stroke). This may be due to an ischaemic process (following a blood clot embolus or a propagating thrombus, for example) or a hemorrhagic process (following rupture of a vessel due to trauma, chronic uncontrolled hypertension, or an arteriovenous malformation). The manifestation of symptoms depends on the vessels that were damaged and the region of the brain that they supply. Basilar strokes are uncommon but may result from a ruptured basilar aneurysm or basilar artery occlusion.

Basilar artery aneurysm

An aneurysm is an abnormal dilatation of the blood vessel wall that involves all three muscular layers of the vessel. They often occur in areas where the arterial walls are thin or weak. The circle of Willis is the most common site of aneurysm formation – with the middle cerebral artery being the most frequently affected vessel. Although it is rare to see a basilar trunk artery aneurysm (an aneurysm occurring distal to the formation and proximal to the origin of the superior cerebellar artery), they may still occur. The clinical manifestation of cerebral aneurysms depends on:

the structures that are adjacent to it
whether or not it is ruptured
the structures supplied by the vessel in question

Ruptured basilar aneurysms may present as subarachnoid hemorrhage or a hemorrhagic stroke. The symptoms experienced will be similar to those seen in cerebellar dysfunction (ataxia, dysdiadochokinesia, vomiting, cardiac arrhythmias, etc.). If the aneurysm remains unruptured but is relatively large, it may result in compression of nearby nerves. The may result in focal deficits related to the affected area of the brain. For example, if the aneurysm compresses the facial nerve (CN VII) then the patient may have facial nerve palsy, resulting in facial hemiparesis (weakness of the muscles of facial expression on half of the face).

Basilar artery occlusion

A thrombus refers to a blood clot that has formed within a blood vessel and obstructs the flow of blood through that lumen. These clots may cause problems locally where they originated or may break off and migrate to occlude distal blood vessels. The latter process is known as an embolism. With respect to the basilar artery, thrombosis or occlusion of this vessel is associated with a very poor outcome. Some individuals present with an acute onset thrombosis, while others have a more gradual, indolent course. Eventually, patients will experience difficulty with speech (dysarthria), visual disturbances (diplopia, pupillary changes), nausea and vomiting, vertigo (dizziness), cranial nerve palsies, and altered consciousness.

Improved outcome for these patients is associated with early detection (using magnetic resonance or computed tomographic imaging) and early treatment (thrombolysis or thrombectomy) to restore blood flow to the affected areas.

Sources

All content published on Kenhub is reviewed by medical and anatomy experts. The information we provide is grounded on academic literature and peer-reviewed research. Kenhub does not provide medical advice. You can learn more about our content creation and review standards by reading our content quality guidelines.

References:

Cruz-Flores, S., & Muengtaweepongsa, S. (2019). Basilar Artery Thrombosis: Background, Anatomy, Pathophysiology. Retrieved from https://emedicine.medscape.com/article/1161044-overview#a3
Fix, J., & Brueckner, J. (2009). High-yield neuroanatomy (4th ed.). Philadelphia, Pa.: Wolters Kluwer, Lippincott, Williams et Wilkins.
Giffin, N. (2001). Basilar artery aneurysm with autonomic features: an interesting pathophysiological problem. Journal Of Neurology, Neurosurgery & Psychiatry, 71(6), 805-808. doi: 10.1136/jnnp.71.6.805
Haines, D. (2013). Fundamental neuroscience for basic and clinical applications (4th ed.). Elsevier Saunders.
Kiernan, J., Barr, M., & Rajakumar, N. (2013). Barr's the human nervous system (10th ed.). Wolters Kluwer Lippincott, Williams, And Wilks.
Menshawi, K., Mohr, J., & Gutierrez, J. (2015). A Functional Perspective on the Embryology and Anatomy of the Cerebral Blood Supply. Journal Of Stroke, 17(2), 144. doi: 10.5853/jos.2015.17.2.144
Netter, F. (2014). Atlas of human anatomy (6th ed.). Philadelphia: Elsevier Saunders.
Saliou, G., Sacho, R., Power, S., Kostynskyy, A., Willinsky, R., & Tymianski, M. et al. (2015). Natural History and Management of Basilar Trunk Artery Aneurysms. Stroke, 46(4), 948-953. doi: 10.1161/strokeaha.114.006909
Snell, R. (2010). Clinical neuroanatomy (10th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins.
Standring, S., & Gray, H. (2008). Gray's anatomy (42nd ed.). Edinburgh: Churchill Livingstone/Elsevier.

Layout:

Adrian Rad

Illustrators:

Basilar artery, its branches and other arteries of the brain (diagram) - Paul Kim
Circle of Willis (diagram) - Paul Kim

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