Patient-specific computational fluid dynamics modeling of anterior communicating artery aneurysms: a study of the sensitivity of intra-aneurysmal flow patterns to flow conditions in the carotid arteries

Abstract

Background and purpose: The purpose of this study was to investigate the effects of unequal physiologic flow conditions in the internal carotid arteries (ICAs) on the hemodynamics of anterior communicating artery aneurysms.

Methods: Patient-specific computational fluid dynamics models of 2 cerebral aneurysms were constructed from bilateral 3D rotational angiograms. The flow dynamics of the aneurysm sac were analyzed under the effect of unequal mean flows, phase shifts, and waveforms between the ICAs. A total of 9 simulations were performed for each patient; cine flow velocity simulations and unsteady wall shear stress (WSS) maps were created for each flow condition. Time-dependent curves of average WSS magnitude over selected regions on the aneurysms were constructed.

Results: Mean flow unbalances in the feeding vessels tended to shift the regions of elevated WSS towards the dominating inflow jet and to change the magnitude of the WSS peaks. The overall qualitative appearance of the WSS distribution and velocity simulations was not substantially affected. Phase and waveform asymmetry increased the temporal complexity of the hemodynamic patterns and tended to destabilize the flow pattern.

Conclusions: Differences in the relative phase and waveform shape in ICAs can significantly affect the complexity and stability of the hemodynamic force distributions. The magnitude of these effects is related to the geometry of the aneurysm and the feeding vessels. Conditions affecting the flow characteristics in the parent arteries of cerebral aneurysms with more than 1 avenue of inflow should be incorporated into flow models.

Fig 1.

Construction of 2 vascular models of AComA aneurysms from bilateral 3D rotational angiograms. The top row corresponds to patient 1, whereas the bottom row corresponds to patient 2. From left to right, the columns show volume renderings of the 3D rotational angiograms obtained by contrast injection in the right and left ICAs, the coregistered 3D rotational angiograms, and the reconstructed vascular models.

Fig 2.

Flow waveforms used in the numeric models of aneurysm hemodynamics.

Fig 3.

Visualization of the inflow and intra-aneurysmal flow patterns: Instantaneous streamlines at peak systole of the base case (1) are plotted for patient 1 (A) and patient 2 (B). The streamlines originating in the left and right A1 segments are rendered in red and light blue, respectively. The dominance of the left inflow in patient 2 and the more symmetric inflow pattern of patient 1 can be clearly seen.

Fig 4.

Selected regions for comparison of WSSs obtained under different flow conditions. The left and right panels correspond to the aneurysms of patients 1 and 2, respectively.

Fig 5.

Average WSS magnitude over each region of patient 1 for the flow conditions listed in the Table. WSS magnitudes are in dynes per square centimeter, and time is in percentage of the cardiac cycle.

Fig 6.

Average WSS magnitude over each region of patient 2 for the flow conditions listed in the Table. WSS magnitudes are in dynes per square centimeter, and time is in percentage of the cardiac cycle.

Fig 7.

Visualizations of the instantaneous WSS distribution over the aneurysm of patient 1. Each column corresponds to each of the 4 selected instants of time defined in Fig 5. Each row corresponds to each of the 9 flow conditions listed in the Table. The regions defined in Fig 4 (left) are also shown for reference. WSS magnitudes range from 0 (blue) to 200 dyne/cm² (magenta).

Fig 8.

Visualizations of the instantaneous WSS distribution over the aneurysm of patient 2. Each column corresponds to each of the 4 selected instants of time defined in Fig 6. Each row corresponds to each of the 9 flow conditions listed in the Table. The regions defined in Fig 4 (right) are also shown for reference. WSS magnitudes range from 0 (blue) to 200 dyne/cm² (magenta).