Table 2:

Variations in the circle of Willis and volume flow rates

Variations in the Circle of Willis“Textbook” Type (n = 105)A1 Hypoplasia (n = 6)P1 Hypoplasia (n = 6)
Total volume flow (mL/min) (mean ± SD)781 ± 151744 ± 119763 ± 129
Right internal carotid artery or internal carotid artery ipsilateral to hypoplastic A1 or P1311 ± 73236 ± 48355 ± 66
Left internal carotid artery or internal carotid artery contralateral to hypoplastic A1 to P1304 ± 74367 ± 67317 ± 60
Basilar artery165 ± 43141 ± 3990 ± 24
  • Note:— A1 indicates precommunicating segment of the anterior cerebral artery; P1, precommunicating segment of the posterior cerebral artery.