From: Types of the cerebral arterial circle (circle of Willis) in a Sri Lankan Population
 | Author | Riggs and Rupp 1963,[2] | El Khamlichi et al., 1985, [16] | Fisher 1965,[17] | Lazorthes et al., 1979,[18] | Eftekhar et al., 2006,[19] | Present study |
---|---|---|---|---|---|---|---|
 | Country | USA (1) | Morocco | USA (2) | France | Iran | Sri Lanka |
 | Total brains | 994 | 100 | 414 | 200 | 102b | 225 |
Types | Configuration | Â | Â | Â | Â | Â | Â |
1 | Typical | 192(19) | 18(18) | 20(5) | 29(14.5) | 29(28) | 32(14) |
2 | all segments hypoplastic | 54(5) | 0(0) | 0(0) | 10(5) | 0(0) | 0(0) |
3 | hypoplastic AcoA | 91(9) | 11(11) | 6(1) | 9(4.5) | 0(0) | 32(14) |
4 | Unilateral hypoplastic PcoA | 88(9) | 14(14) | 24(6) | 28(14) | 20(20) | 26(11.5) |
5 | Unilateral hypoplastic PcoA and AcoA | 41(4) | 6(6) | 12(3) | 10(5) | 4(4) | 15(7) |
6 | Bilateral hypoplastic PcoAs; | 126(13) | 24(24) | 131(32) | 44(22) | 28(27) | 52(23) |
7 | Bilateral hypoplastic PcoAs and hypoplastic AcoA | 67(7) | 10(10) | 58(14) | 34(17) | 4(4) | 37(16) |
8 | hypoplastic A1 | 38(5) | 2(2) | 0(0) | 3(1.5) | 0(0) | 6 (3) |
9 | Unilateral hypoplastic P1 | 47(5) | 3(3) | 4(0.9) | 5(2.5) | 1(0.9) | 2(0.8) |
10 | Bilateral hypoplastic P1s | 33(3) | 1(1) | 16(4) | 6(3) | 0(0) | 1(0.4) |
11 | hypoplastic P1 and contralateral A1 | 2(0.2) | 0(0) | 10(2) | 0(0) | 0(0) | 0(0) |
12 | hypoplastic P1 and ipsilateral A1 | 20(2) | 1(1) | 1(0.2) | 3(1.5) | 1(0.9) | 4 (2) |
13 | Bilateral hypoplastic P1s and A1 | 5(0.5) | 0(0) | 3(0.7) | 1(0.5) | 0(0) | 1(0.4) |
14 | hypoplastic A1 and contralateral PcoA | 7(0.7) | 0(0) | 1(0.2) | 1(0.5) | 0(0) | 0(0) |
15 | Hypoplastic AcoA and P1 | 35(3.5) | 4(4) | 0(0) | 4(2) | 1(0.9) | 6(3) |
16 | hypoplastic PcoA, ipsilateral A1 and AcoA | 16(2) | 3(3) | 2(0.4) | 2(1) | 0(0) | 0(0) |
17 | hypoplastic PcoA and contralateral P1 | 26(3) | 0(0) | 46(11) | 3(1.5) | 2(2) | 1(0.4) |
18 | A1 and bilateral hypoplastic PcoAs | 58(6) | 0(0) | 21(5.0) | 6(3) | 0(0) | 4(2) |
19 | hypoplastic PcoA, AcoA and contralateral P1 | 17(2) | 1(1) | 28(7) | 1(0.5) | 1(0.9) | 0(0) |
20 | hypoplastic P1, contralateral PcoA and ipsilateral A1 | 10(1) | 1(1) | 5(1) | 0(0) | 0(0) | 0(0) |
21 | Bilateral hypoplastic P1s and AcoA | 13(1) | 0(0) | 10(2) | 1(0.5) | 0(0) | 1(0.4) |
22 | hypoplastic PcoA, ipsilateral A1 and contralateral P1 | 3(0.3) | 0(0) | 8(2) | 0(0) | 0(0) | 0(0) |
Others | Â | 5(0.5) | 1(1) | 8(2) | 0(0) | 1(0.9) | 5(2) |