CIRCLE OF WILLIS-NORMAL VARIANTS

SUMMARY

1. ICA: persistent embryonic cervical ICA branches to vertebrobasilar system, persistent trigeminal a., persistent hypoglossal a.

2. ACA: hypoplastic A1 segments, azygous ACA, duplicated/fenestrated segments

3. MCA: rare; can be fenestration, duplication

4. PCOM: hypoplastic PCOM

5. PCA: fetal PCA (arises from ICA instead of vertebrobasilar system)



Image: Circle of Willis. Netter. (2014). Atlas of Human Anatomy, Sixth Edition. 6th ed. Elsevier.

Reference(s)

R.M.H McMinn (1998). Last’s anatomy: regional and applied. Edinburgh: Churchill Livingstone. Get it on Amazon.
Drake, Richard L., et al. Gray's Anatomy for Students. Elsevier, 2023. Get it on Amazon.