Could A1 Aplasia or Hypoplasia Affect the Morphology and Rupture Risk of Anterior Communicating Artery Aneurysm?

Abstract

Objective : Anterior communicating artery (Acom) aneurysm is one of the most common intracranial aneurysms, constituting approximately 30–35% of all aneurysm formation in the brain. Anatomically, the H-complex (the anatomic morphology of both A1 to A2 segments) is thought to affects the nature of the Acom aneurysm due to its close relationship with the hemodynamics of the vessel. Therefore, we investigated the relative risk factors of aneurysmal rupture, especially focusing on H-complex morphology of the Acom.Methods : From January 2016 to December 2020, a total of 209 patients who underwent surgery, including clipping and coiling for Acom aneurysm in our institution were reviewed. There were 102 cases of ruptured aneurysm and 107 cases of unruptured aneurysm. The baseline morphology of aneurysms was investigated and the relationship between the H-complex and the clinical characteristics of patients with Acom aneurysms was assessed.Results : Of the 209 patients, 109 patients (52.1%) had symmetrical A1, 79 patients (37.8%) had unilateral hypoplastic A1, and 21 patients (10.0%) had aplastic A1. The hypoplastic A1 group and the aplastic A1 group were grouped together as unilateral dominancy of A1, and were compared with the symmetrical A1 group. There was no significant difference in demographic characteristics and radiological findings of Acom aneurysms between two groups. However, when dichotomizing the patients into ruptured cases and unruptured cases, unilateral dominance of the A1 segment was associated with aneurysmal rupture with statistical significance (<i>p</i>=0.011).Conclusion : These results suggest that the unilateral dominance of the A1 segment does not have a significant effect on the morphology of Acom aneurysms, but contributes to aneurysmal rupture. Thus, we can better understand the effects of hemodynamics on Acom aneurysm.

Anatomical variations in the Circle of Willis and the formation and rupture of intracranial aneurysms: A systematic review and meta-analysis

“…Overall, the included cross-sectional studies that were assessed using the AHRQ scale received 6–9 scores, while the cohort and case-control studies that were assessed using NOS received 6–7 and 5–7 scores, respectively. Five studies were of high quality ( 15 , 19 , 20 , 26 , 29 ), while the others were of medium quality. A summary of the study quality assessment is provided in Supplementary Tables 4 – 6 .…”

Geometry and Symmetry of Willis’ Circle and Middle Cerebral Artery Aneurysms Development

“…The PCom tract was defined as "fetal" when the proximal PCA (P1 segment) was hypoplastic or absent and PCom served as the main dominant source of blood supply to the PCA territory [20]. The vessel was considered hypoplastic when the width was less than 50% of the width of the contralateral corresponding larger vessel [21]. Measurements were performed on TC-angiograms in the arterial phase using the maximum intensity projection (MIP) images.…”

“…However, the development of aneurysms cannot be explained solely through an increased impingement of axial flow to an apex [36,37], and some other hemodynamic factors such as secondary factors flow as well as the local structure must be taken into consideration. Also, aneurysms develop more often in bifurcations with relatively sharp angles, where the bloodstream deviates significantly from the direction of flow of the parent artery, than in bifurcations with more obtuse angles, where the bloodstream deviates relatively little from the direction of flow of the parent artery [3,21,26]. This last geometrical characteristic would seem to be the most important predisposing feature compared with the circle of Willis' symmetry for the risk of MCA aneurysm development, aneurysms that are often more similar to a bifurcation dysplasia than true saccular aneurysms [38][39][40].…”

Variantes anatómicas del segmento anterior del polígono de Willis: relación con aneurismas cerebrales

“…En estos casos, el segmento A1 contralateral irriga todo el territorio de la ACA. Se cree que esta relación surge a partir del mayor estrés hemodinámico que ocurre debido al flujo aumentado a través de la ACA, lo que puede predisponer a la formación de aneurismas (11,14). En una investigación en la que se definió hipoplasia del segmento A1 de la ACA como un diámetro menor al 50% del segmento A1 contralateral, se evidenció una asociación a favor de la formación de aneurismas en esta variante anatómica.…”