Circle of Willis is an important arterial communication that supplies the forebrain (telencephalon, diencephalon and optic vesicle) and often frequently tested in the exams. Circle of Willis receives blood from:
- Vertebrobasilar system: Basilar artery which gives off Posterio Cerebral Arteries (PCA) and Posterior communicating arteries which are the branches of PCA
- Internal Carotid Artery System: Gives off other arteries of Circle of Willis
Here, we will learn a mnemonic to draw the circle of willis and intracranial course of Internal Carotid Artery (ICA).
Step-wise instructions for drawing the circle of willis:
1. Draw a Circle – Circle of Willis is a circle of arteries.
Now write the “Willis” around this circle:
2. Write a large “W” at the inferior of circle – this represents Posterior Cerebral Arteries (PCA) which arises from a single basilar artery.
3. Write a horizontal “i” at the sides of the circle – this represents Middle Cerebral Artery (MCA) outside the circle and Internal Cerebral Artery (ICA) inside the circle.
4. Write “l l” at the superior of the circle – this represents the Anterior Cerebral Arteries (ACA) along with the part of circle between the MCA-ICA and Anterior communicating artery.
5. Write a horizontal “i” at the sides of the circle – this represents Middle Cerebral Artery (MCA) outside the circle and Internal Cerebral Artery (ICA) inside the circle.
Now, the intra-cranial course of Internal Carotid Artery:
6. Write a horizontal “S” – starting from carotid canal and ending in foramen lacerum.
7. Write another horizontal “S” beginning from the end of previous “S” –
- starting from foramen lacerum and then
- forming “S” shaped carotid siphon within cavernous sinus and then
- ending at the level of anterior clinoid process
- supraclinoid segment of ICA gives of branches to form Circle of Willis
| Artery | Function/supply |
| Anterior cerebral (ACA) | Frontal lobes, Superior-Medial parietal lobes |
| Anterior communicating | Connects ACA |
| Middle cerebral (MCA) | Lateral cerebral hemispheres (mostly), Basal ganglia, Internal capsule |
| Posterior communicating | Joins PCA to terminal trifurcation of ICA |
| Posterior cerebral (PCA) | Occipital lobes |
| Superior cerebellar (SCA) | Superior cerebellum, Parts of midbrain |
| Basilar | Brainstem |
| Anterior Inferior Cerebellar (AICA) | Anterior inferior cerebellum |
| Vertebral | Deliver blood to circle of Willis |
He is the section editor of Orthopedics in Epomedicine. He searches for and share simpler ways to make complicated medical topics simple. He also loves writing poetry, listening and playing music.