Relationship between A1 segment hypoplasia and the site of cerebral infarction: A single-center retrospective study

Background: The Circle of Willis (CoW) is a key collateral pathway that enables communication between the anterior and posterior cerebral circulations. However, anatomical variations deficiency of the A1 segment of the anterior cerebral artery can alter hemodynamics and may compromise this collateral function. While incomplete CoW configurations have been linked to aneurysm formation and altered patterns of hemorrhage, their role in the distribution of cerebral infarctions remains controversial. We investigated the impact of A1 segment deficiency within an incomplete CoW on infarct distribution by stroke type. Method: We retrospectively analyzed patients with unilateral anterior circulation infarction admitted between April 2017 and March 2023. The CoW was assessed by magnetic resonance angiography (MRA). A1 segment hypoplasia was defined as a segment diameter <1 mm; A1 deficiency was defined as non-visualization on MRA. The side with hypoplasia or aplasia was defined as the minor side, and the contralateral side as dominant. We assessed whether infarction occurred on the minor or dominant side. Result: Among 198 patients with unilateral anterior circulation infarction classified as lacunar, cardioembolic stroke (CES), or embolic stroke of undetermined source (ESUS), 30% had A1 hypoplasia or aplasia, with similar prevalence across subtypes. Infarcts occurred on the dominant A1 side in 53% of lacunar, 55% of ESUS, and 75% of CES cases. Although this difference was not statistically significant (p = 0.43), CES showed a tendency toward dominant-side infarction. Conclusion: A1 deficiency rates were similar across stroke types; in CES, infarcts tended to occur on the dominant A1 side.