The bifurcation angle is associated with the progression of saccular aneurysms

Abstract

The role of the bifurcation angle in progression of saccular intracranial aneurysms (sIAs) has been undetermined. We, therefore, assessed the association of bifurcation angles with aneurysm progression using a bifurcation-type aneurysm model in rats and anterior communicating artery aneurysms in a multicenter case-control study. Aneurysm progression was defined as growth by ≥ 1 mm or rupture during observation, and controls as progression-free for 30 days in rats and ≥ 36 months in humans. In the rat model, baseline bifurcation angles were significantly wider in progressive aneurysms than in stable ones. In the case-control study, 27 and 65 patients were enrolled in the progression and control groups. Inter-observer agreement for the presence or absence of the growth was excellent (κ coefficient, 0.82; 95% CI, 0.61-1.0). Multivariate logistic regression analysis showed that wider baseline bifurcation angles were significantly associated with subsequent progressions. The odds ratio for the progression of the second (145°-179°) or third (180°-274°) tertiles compared to the first tertile (46°-143°) were 5.5 (95% CI, 1.3-35). Besides, the bifurcation angle was positively correlated with the size of aneurysms (Spearman's rho, 0.39; P = 0.00014). The present study suggests the usefulness of the bifurcation angle for predicting the progression of sIAs.

Figure 1

Schematic diagrams showing angle measurement at the anterior communicating artery (Acom)-anterior cerebral artery (ACA) bifurcation. The angles formed between the Acom and the A2 segment (the Acom/A2 angle) (A) and between the A1 segment and the plane containing both the Acom and the A2 segment (the A1/Acom-A2 plane angle) (B) are presented.

Figure 2

Present saccular aneurysm model at the surgically created common carotid artery (CCA) bifurcation in rats. (A) A macroscopic view of the surgically created CCA bifurcation. (B) Representative magnetic resonance angiography findings of the CCA bifurcation one month after aneurysm induction demonstrating the three categories: a growing aneurysm (An) (the left panel), a stable An (the middle panel), and no An (the right panel). These images were created using Horos visualization software (64-bit, version 3.6.6, https://horosproject.org). Systolic blood pressure (C) and body weight (D) before and on the 5th and 10th days after aneurysm induction. Data are presented as means ± SD. Statistical comparisons were performed by the Steel-Dwass test at each time point.

Figure 3

The association of the bifurcation angle with aneurysm progression in rats. (A) A schematic representation of the study design. Magnetic resonance imaging (MRI) includes MR angiography and cardiac-gated two-dimensional phase-contrast MRI. (B) Sequential assessments by MR angiography showing the size of growing (n = 7) and stable (n = 8) aneurysms (An). Data are presented as means ± SD. (C) MR angiography showing the bifurcation angle and the point where blood flow volume estimated by phase-contrast MR imaging was measured. This image was created using Horos visualization software (64-bit, version 3.6.6, https://horosproject.org). (D) Comparison of the bifurcation angle (the left panel) and blood flow volume at peak systole (the middle panel) and end-diastole (the right panel) between growing (n = 7), stable (n = 8), and no An (n = 6) on the 5th day after the aneurysm induction. Data are shown as box-and-whisker plots. Statistical comparisons were performed by the Steel-Dwass test.

Figure 4

Patient enrollment flowchart in the case–control study. Acom anterior communicating artery.

Figure 5

Scatter diagrams with a linear regression line showing the correlation between the largest dimension of anterior communicating artery (Acom) aneurysms and the angle formed between the Acom and the A2 segment of the ACA (Acom/A2 angle). Spearman’s correlation analysis was performed at each time point before (A) and after (B) progression.