Proximal Stenosis Is Associated with Rupture Status in Middle Cerebral Artery Aneurysms

Hemodynamic factors impact cerebral aneurysm development and progression. Parent vessel architectural features, such as caliber, curvature, and angle, can affect downstream pressure and shear stress.

To investigate the association between proximal parent vessel stenosis and aneurysm rupture status at the middle cerebral artery (MCA) bifurcation.

Catheter 3-dimensional rotational angiographic datasets from 69 Japanese patients with MCA aneurysms (58 unruptured/11 ruptured) were analyzed. The narrowest cross-sectional area of the M1 segment was evaluated through equidistant cross-sectional plane cuts along the M1 length. The degree of stenosis relative to M1 size (StenosisIndex) and the distance from stenosis to the aneurysm neck (StenosisAnDist) were statistically evaluated. The effects of StenosisIndex and StenosisAnDist were determined in parametric aneurysm models with/without stenosis using computational fluid dynamic and fluid-structure interaction simulations.

MCA harboring ruptured aneurysms had significantly greater StenosisIndex (0.31 ± 0.21 vs. 0.17 ± 0.14, P = 0.01), indicative of greater narrowing, and shorter StenosisAnDist (4.26 ± 1.91 vs. 6.94 ± 4.06 mm, P = 0.02) compared with unruptured aneurysms. Multivariate analysis combining StenosisIndex and StenosisAnDist resulted in P = 0.003, area under the curve = 0.81 (80% sensitivity, 74% specificity). Computational fluid dynamic and fluid-structure interaction simulations identified a synergetic effect of high stenosis and short StenosisAnDist in inducing greater aneurysm inflow velocity and deeper jet penetration, greater dome pressure, and greater tensile stress in the aneurysm wall.

Ruptured status in bifurcation MCA aneurysms was associated with severity of proximal M1 stenosis and its proximity to the aneurysm neck, a novel risk factor, which acts by increasing aneurysm dome wall tension, and should be considered in investigations of rupture risk stratification.