Aneurysm rupture risk is incredibly difficult to predict. Many risk factors have been identified already, but the impact of hemodynamics on aneurysm rupture risk remains unclear. Computational fluid dynamics (CFD) is a virtual technique that enables researchers to simulate blood flow patterns in vessels, and even in small intracranial aneurysms. In the field of CFD, the single most important factor influencing the results is the vascular geometry. This vascular geometry is generally derived from clinically used angiographic imaging, and due to varying quality and detail of the available modalities, the accuracy of the vascular geometry also varies greatly. We have always tried to use the best available aneurysm geometries for CFD, which in practice meant that only cases that had a 3D rotational angiography (3DRA) of the specific arterial segment could be included.

During the earlier pilot phases of our larger cohort study, we found a discrepancy between the 2D digital subtraction angiography and the corresponding 3DRA. Inherent to the acquisition technique and reconstruction algorithm of 3DRA, there is a blooming effect (or smudging) of high-density structures if they are in close proximity to each other. In

arteries this is not an issue, but when it happens in aneurysm neck areas, the subsequent reconstruction algorithm is portraying the aneurysm neck larger than in reality (neck size overestimation). We showed that this neck size overestimation can, in specific cases, have a profound effect on the calculated intra-aneurysmal hemodynamics with CFD.¹ We considered these findings very important to the research field of CFD. The main message is that the criterion standard in vascular geometry, 3DRA, is not without flaws.

Another line of research considers the differences in geometry between ruptured and unruptured aneurysms. In this paper we have shown that an aneurysm geometry is often different when imaged after rupture.² Although it is nearly impossible to prove direct causality between the rupture and apparent changes in vascular geometry, the geometric differences between the 2 time points alone is disconcerting. In aneurysm rupture risk factor identification studies, aneurysm geometry change associated with rupture is usually not taken into account, because aneurysms are rarely imaged before they rupture. Our findings should change the way we look at all comparisons between ruptured and unruptured aneurysms.

References

1. Schneiders JJ, Marquering HA, Antiga L, et al. Intracranial aneurysm neck size overestimation with 3D rotational angiography: the impact on intra-aneurysmal hemodynamics simulated with computational fluid dynamics. AJNR Am J Neuroradiol 2013;34:121–28, 10.3174/ajnr.A3179
2. Schneiders JJ, Marquering HA, van den Berg R, et al. Rupture-associated changes of cerebral aneurysm geometry: high-resolution 3D imaging before and after rupture. AJNR Am J Neuroradiol 2014;35:1358–62, 10.3174/ajnr.A3866

 

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