Corpus: Cerebral arterial circle

The Circulus arteriosus cerebri is an arterial vascular ring at the base of the brain that supplies blood to the brain.

The cerebral arterial ring is made up of the following vessels from anterior to posterior:

• Arteria communicans anterior (unpaired)
• Arteria cerebri anterior (left and right)
• Arteria carotis interna (left and right) or its direct continuation, the arteria cerebri media
• Posterior communicating artery (left and right)
• Posterior cerebral artery (left and right), both of which arise from the basilar artery

The two middle cerebral arteries are not included in the cerebral arterial circle.

The arterial circle lies in the cisterna basalis and frames the following structures from front to back:

• Lamina terminalis
• Optic chiasm
• Tuber cinereum
• Corpora mamillaria
• interpeduncular fossa

The anatomy of the cerebral arterial circle is extremely varied. The significance of the vessels that feed blood into the cerebral arterial circle can therefore vary greatly. In particular, the anastomoses via the communicans arteries vary greatly between individuals.

A closed arterial ring is present in around 90 to 95 % of cases. In 40 to 50 % of people, however, there are variants that particularly affect the formation and calibre of the posterior communicating arteries. Rarely, they are completely absent or one of the two posterior cerebral arteries emerges from the ACI (foetal PCA).

The cerebral arterial circle forms a collateral circulation (anastomosis), which primarily serves to equalise the pressure between the different flow areas and thus ensures an even blood supply to the brain. If one of the arteries involved is chronically blocked, blood flow to the brain can be maintained within certain limits.

It is also suspected that the cerebral arterial circle may play a role in the attenuation of pulse waves in the brain.

Cerebral aneurysms are often found in the region of the arterial circle. Ruptures lead to a subarachnoid haemorrhage.

• 3D model: Dr Claudia Krebs (Faculty Lead) University of British Columbia