Quantitative comparison of the dynamic flow waveform changes in 12 ruptured and 29 unruptured ICA–ophthalmic artery aneurysms

Abstract

IntroductionStudies have reported a correlation between blood flow dynamics in the cardiac cycle and vascular diseases, but research to analyze the dynamic changes of flow in cerebral aneurysms is limited. This quantitative study investigates the temporal changes in flow during a cardiac cycle (flow waveform) in different regions of aneurysms and their association with aneurysm rupture.MethodsTwelve ruptured and 29 unruptured aneurysms from the internal carotid artery–ophthalmic artery segment were studied. Patient-specific aneurysm data were implemented to simulate blood flow. The temporal flow changes at different regions of the aneurysm were recorded to compare the flow waveforms.ResultsIn more than 60 % of the cases, peak flow in the aneurysm sac occurred after peak flow in the artery. Flow rate varied among cases and no correlation with rupture, aneurysm flow rate, and aneurysm size was found. Higher pulsatility within aneurysm sacs was found when comparing with the parent artery (P < 0.001). Pulsatility was high throughout ruptured aneurysms, but increased from neck to dome in unruptured ones (P = 0.021). Significant changes between inflow and outflow flow profile were found in unruptured aneurysms (P = 0.023), but not in ruptured aneurysms.ConclusionQuantitative analysis which considers temporal blood flow changes appears to provide additional information which is not apparent from aneurysmal flow at a single time point (i.e., peak of systole). By considering the flow waveform throughout the cardiac cycle, statistically significant differences were found between ruptured and unruptured cases — for flow profile, pulsatility and timing of peak flow.

Morphologic and Hemodynamic Risk Factors in Ruptured Aneurysms Imaged before and after Rupture

“…As previously reported by Chien et al 6 and Baek et al, 27 aneurysm and vascular shape affect pulsatile flow properties at the aneurysm site. These effects are made especially clear when a single, standard flow profile is used for hemodynamic analysis of all cases, as is the standard method and was done in this research.…”

“…For all cases, a standard ICA flow profile acquired from a healthy subject with phase-contrast MR imaging was applied. 5,6,18,22 The qualitative hemodynamic risk factors analyzed included aneurysm inflow jet size, flow impingement size, and aneurysmal flow pattern, as proposed by Cebral et al 5 Quantitative hemodynamic risk factors, including normalized wall shear stress (WSS), maximum aneurysm wall shear stress, and pulsatility index were analyzed. 8,15,22 On the basis of the indices proposed by Xiang et al, 15 normalized aneurysm wall shear stress was obtained by averaging wall shear stress over a cardiac cycle (equation 6), and maximum aneurysm wall shear stress was defined as maximum intra-aneurysmal WSS normalized by the average parent artery WSS (equation 7).…”

“…[2][3][4] By analyzing blood flow properties in groups of ruptured and unruptured aneurysms, reports have also shown that certain hemodynamic factors may play an important role in aneurysm rupture. [5][6][7][8][9] However, the morphologic and hemodynamic risk factors analyzed in these studies have generally been identified by analyzing ruptured aneurysms after rupture. Because clinical reports also suggest that aneurysms change due to rupture, how well these risk factors can actually help predict rupture has been controversial.…”

“…The fundamental rationale in aneurysm risk analysis based on comparing ruptured and unruptured aneurysm groups is that aneurysms that rupture have the same risk characteristics in the unruptured and ruptured states. [5][6][7][8][9]13 In that case, the results obtained by comparing ruptured with unruptured aneurysms can help assess the risk of rupture in as-yet-unruptured aneurysms. However, there are limited studies testing this hypothesis.…”

“…4,[6][7][8][14][15][16][17] Our objective was to investigate morphology and flow properties of aneurysms before and after rupture and find whether previously identified risk factors were present in aneurysms before rupture. We sought to identify risk factors that consistently existed in ruptured aneurysms in both unruptured and ruptured states to guide early determination of aneurysm rupture risk.…”