Potent Risk Factor for Aneurysm Formation: Termination Aneurysms of the Anterior Communicating Artery and Detection of A1 Vessel Asymmetry by Flow Dilution

A1 flow configuration on DSA from a single patient with right A1 dominance. A−F, Selective images from angiography after injection of contrast into the right ICA (A, C, and E) and left ICA (B, D, and F) for the same patient. During the pressure of injection into the ICA in the neck (A and B), contrast is seen filling both A2s from each A1. Following release of the pressure of injection, contrast continues showing the early dilution phase (C and D), maintaining both A2s filling from the right A1 (C), while there is substantial dilution of left A2 (D), injected from the left ICA. The late phase in both E and F shows all vessels as dilute. Effectively, there is a mixed supply of left A2 from both A1s, giving the classification of the configuration as “right dominant.”