Introduction: Circle of Willis is the great arterial anastomotic ring at the base of the brain and is an important pathway to maintain adequate blood supply to the brain. In case of arterial occlusion, it is the important source of collaterals to the occluded territory. A detailed knowledge of the normal anatomy of circle of Willis, its anomalies and clinical significance helps the neurosurgeon for planning and keeps away from vascular trauma during surgeries.

Materials and Methods: A retrospective study was conducted on 312 patients (188 men and 124 women). 3 dimensional time of flight Magnetic resonance angiogram technique was used. Variations in the Circle of Willis were evaluated.

Results: The findings show that majority of circle showed anomalies. Percentage of complete circle was slightly higher in males and young subjects. Normal variants are more common in anterior part of the circle and the most common normal variant is the absent anterior communicating artery (34%).

Conclusion: Magnetic resonance angiogram is the sensitive technique for detecting the anatomy of Circle of Willis. Variations in anterior circulation may be asymptomatic and may reduce complications. Knowledge of the presence of Circle of Willis and its variants plays an important role in planning of neurological procedures or may be mistaken for pathologies.

Keywords: Anomalies, absent anterior communicating artery, 3-dimensional time of flight.

1. Dimmick SJ, Faulder KC. Normal variants of the cerebral circulation at multidetector CT angiography. Radiographics. 2009; 29: 1027–43.
2. Kondori BJ, Azemati F, Dadseresht S. Magnetic Resonance Angiographic Study of Anatomic Variations of the Circle of Willis in a Population in Tehran. Arch Iran Med. 2017; 20(4): 235 – 239.
3. Naveen SR, Bhatt V, Karthik GA. Magnetic resonance angiographic evaluation of Circle of Willis: A morphologic study in a tertiary hospital set up. Annals of Indian academy of neurology.2015; 391-397.
4. Krabbe – Hartkamp MJ, Van dergrond J. Investigation of the circle of Willis using MR angiography. Medicamundi .2000; 44(1): 20 -7.

1. Lippert H, Pabst R. cerebral arterial circle (circle of willis) . In:Lippert H, Pabst R, editors. Lippert H, Pabst R, editors. Arterial variations in man: classification and frequency. Bergmann: Munich, Germany; 1985. p. 92–3.
2. Haripriya M, Melani RS, A study of the anatomical variations of the Circle of Willis using Magnetic Resonance Imaging: International Journal of Anatomical Sciences: 2010: 1: 21 – 25.
3. Chen HW, Yen PS, Lee CC, et al. Magnetic resonance angiographic evaluation of circle of Willis in general population: a morphologic study in 507 cases. Chin J Radiol 2004; 29:223–9.
4. Hafez KA, Afifi NM, Saudi FZ. Anatomical variations of the circle of Willis in males and females on 3D MR angiograms. Egyptian J Hospital Med 2007;26:106–21.
5. Alpers BJ, Berry RG, Paddison RM. Anatomical studies of the circle of Willis in normal brain. AMA Arch Neurol  Psychiatry 1959;81:409-18.  
6. Ozaki T, Handa H, Tomimoto K, Hazama F. Anatomical variations of the arterial system of the base of the brain.  Arch JpnChir 1977;46:3-17.  
7. Kapoor K, Singh B, Dewan LI. Variations in the configuration of the circle of Willis. Anat Sci Int 2008;83:96106
8. Macchi C.etal Magnetic resonance angiographic evaluation of circulus arteriosus cerebri (circle of Willis): A morphologic study in 100 human healthy subjects. Ital J Anat Embryol 1996;101:115-23
9. Jongen JC, Franke CL, Soeterboek AA, Versteege CW, Ramos LM, van Gijn J. Blood supply of the posterior cerebral artery by the carotid system on angiograms. J Neurology 2002;249:455-60.  
10. Papantchev V, Hristov S, Todorova D, Naydenov E, Paloff A, Nikolov D, etal. Some variations of the circle of Willis, importat for cerebral protection in aortic surgery - A study in Eastern Europeans. Eur J Cardiothoracic Surg 2007;31:982-9
11. Lee JH et al. relationship between circle of willis morphology on 3D time of flight MR angiograms and transient ischemia during clamping of internal carotid. Artery during carotid endarterectomy. AJNR2004;25:558-64.
12. Brunereau LO, Levy C, Arrive L. Anatomie du polygone de Willis en ARM 3d temps devolavecanalyse des patitions. J Radiol 1995;76:573–5.
13. William AN. Thomas Willis' understanding of cerebrovascular disorders. J Stroke Cerebrovasc Dis 2003;12:280-4. DOI: 10.1016/ j.jstrokecerebrovasdis.2003.09.012.
14. Ustun C. Dr. Thomas Willis' famous eponym: the Circle of Willis. Turk J Med Sci 2004;34:271-4.

Dr K.S.Kaviyavarshini

SMVMCH, Puducherry