A Hemodynamic Mechanism Correlating with the Initiation of MCA Bifurcation Aneurysms

Schematic drawing of the angles measured in our study. A and B, The parent-daughter angle was defined as the angle between the M1 trunk and different M2 branches, and the daughter-daughter angle was the angle between 2 M2 branches. C, In the MCA aneurysm bifurcation, lines L1 and L2 were crossed in the aneurysm neck and then measured to decide on which side of the M2 branch the aneurysm was located. D, The measurements of diameters were performed 5 mm beyond the bifurcation apex.

A, The size of ϕA was significantly different from that of the other 3 parent-daughter angles in the aneurysmal group and the 4 parent-daughter angles in the control group. There were no statistically significant differences among the 3 parent-daughter angles in the aneurysmal group and all 4 parent-daughter angles in the control group. B, The size of γ_A was significantly different from that of another daughter-daughter angle in the aneurysmal group and 2 daughter-daughter angles in the control group. There were no statistically significant differences between the 2 daughter-daughter angles in the control group. C, An optimal threshold of 100.06° for ϕA (area under the curve, 0.903) with 84.1% sensitivity and 81.5% specificity revealed that the daughter artery that is apt to harbor an MCA aneurysm is the artery with a smaller parent-daughter angle. NS indicates no statistical significance (P > .05); asterisk, statistical significance (P < .05).

CFD analysis. A, CFD analysis on an aneurysmal MCA bifurcation shows the initial sites of aneurysms overlap with HPRs and LWSSRs, and these sites incline to the daughter artery with a smaller parent-daughter angle (first row, pressure contour; second row, wall shear stress contour; third row, blood flow direction. See also On-line Digital Content 2). B, CFD analysis of simplified 3D MCA bifurcation models. When a single parent-daughter angle varied from 120° to 30°, HPRs and LWSSRs were displaced from the apex of the bifurcation to the same daughter artery wall (detailed demonstrations are also shown in On-line Digital Content 3); the values of hemodynamic parameters were obtained along the virtual path (black arrows) in the simplified 3D MCA bifurcation models. C and D, The distribution of pressure and wall shear stress shifts along the virtual path when a single parent-daughter angle varies from 120° to 30°. The HPR and LWSSR (black arrows) shift from the apex to the left daughter artery, which has a smaller parent-daughter angle. The red line represents the bifurcation apex, the left part represents the daughter artery with a variable angle, and the right part represents the daughter artery with a fixed angle.