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

Figure 1

Ideographs 1 and 2 in the present study. Ideograph 1: type I: normal, balanced development of bilateral A1 segment, where ACoA exists; type II: noneven integral type, that is, ACoA exists and unilateral A1 segment is I^°; type III: maldevelopment type; type IV: A1 segment is absent. Type V1: A1 segment is evenly developed while ACoA is absent. Type V2: A1 segment is not balanced and ACoA is absent. Ideograph 2: (a) normal posterior circulation; (b) bilateral quasi-FTP type; (c) unilateral quasi-FTP type; (d) bilateral PCoA absent with normal PCA at both left and right rides; (e) unilateral PCoA exists, while contralateral PCoA is absent; (f) unilateral quasi-FTP, with one PcoA absent; (g) unilateral pure FTP, with one PCoA absent; (h) unilateral pure FTP; (i) unilateral pure FTP combining contralateral quasi-FTP; (j) bilateral pure FTP; (k) unilateral duel PCA, extended from internal carotid artery and basilar artery, respectively, without any connection between the two.