Table 2:

Reference values of the prevalence of anatomic variations of the CoW in a group of 65 infants (24 term-born, 41 preterm-at-term) with normal MR imaging findings

	Term (normal MRI) n = 24	Preterm (normal MRI) n = 41	P Value	Mean
Completeness of CoW	9 in 24 (37.5%)	18 in 41 (44%)	.405	41.50%
AcomA absence/hypoplasia	6 in 24 (25%)	6 in 41 (14.6%)	.237	18.50%
PcomA absence/hypoplasia	13 in 48 (27%)	26 in 82 (31.7%)	.363	30%
A1 segment of ACA absence/hypoplasia	5 in 48 (10.4%)	1 in 82 (1.2%)	.026*	4.60%
P1 segment of PCA absence/hypoplasia	4 in 48 (8.3%)	4 in 82 (4.8%)	.332	6.10%
Fetal-type origin of PCA	14 in 48 (29%)	22 in 82 (26.8%)	.463	27.70%
Transitional-configuration origin of PCA	6 in 48 (12.5%)	4 in 82 (4.8%)	.11	5.40%
Bilateral fetal-type origin	8 in 14 (57.1%)	14 in 22 (63.6%)	.482	61.10%
Bilaterally absent PcomA	6 in 13 (46.2%)	14 in 26 (53.8%)	.455	51.30%

Note:—CoW indicates circle of Willis; MRI, MR imaging; AcomA, anterior communicating artery; PcomA, posterior communicating artery; ACA, anterior cerebral artery; PCA, posterior cerebral artery.

^*Statistically significant.