Seventy-eight subjects (37.1% of all cases) were included in the PA group, including 15 in the PA1 group (7.1%) with a unilateral F-PCA and absent contralateral PcomAA, 45 in the PA2 group (21.4%) with ≥50% PcomA asymmetry, and 18 in the PA3 group (8.6%) with < 50% PcomA asymmetry. Twenty-three subjects had both A1 and PcomA asymmetry. In these subjects, the dominant A1 was most likely to be on the same side as the non-dominant PcomA (19 patients, P < 0.001, McNemar’s test). Only 4 subjects had the dominant A1 and dominant PcomA on the same side.