MRA Study on Variation of the Circle of Willis in Healthy Chinese Male Adults

Table 3

Developmental variation of the A1 segment.

A1 segment	Normal (side)	Variation (side)			Mean rank sum
		Mild variation	Hypoplasia	Absence
L	2041	135	56	14	2130.10
R	1817	198	150	81	2362.90

Note: , .