Introduction
: Morphological and hemodynamic characteristics have been reported to be involved in the rupture of cerebral aneurysms. Therefore, geometrical measurements of cerebral aneurysms and blood flow analysis using computational fluid dynamics (CFD) have been conducted. Some previous studies investigated the rupture risk factors from cerebral arterial geometries that were taken before the rupture (pre‐rupture), and the others used geometries taken after the rupture (post‐rupture). However, aneurysm rupture may alter arterial geometries and CFD simulation results. The aim of this study is to evaluate the morphological and hemodynamic alternations due to cerebral aneurysm rupture.
Methods
: We identified 21 cerebral aneurysms (ICA: 9, MCA: 3, ACA: 4, BA: 3, VA: 2) which had ruptured during the follow‐up terms. Each case had at longest two‐years term between the rupture date and the latest angiographic date before the aneurysm rupture (pre‐rupture). The post‐rupture arterial geometries were acquired preoperatively for subarachnoid hemorrhage. We used the arterial geometries reconstructed from computed tomography angiography or digital subtraction angiography images for conducting morphological measurements and CFD simulations. We performed transient blood flow simulations for two heart pulse cycles in the CFD simulations. We obtained five morphological parameters and 24 hemodynamic parameters considered as the rupture risk factors. Finally, we conducted Wilcoxon’s signed‐rank sum test between the parameters obtained from pre‐ and post‐rupture aneurysms to specify altered parameters due to the aneurysm rupture. We also calculated the change rate (CR) based on the value in pre‐rupture for parameters that had a statistical significance to investigate the alternation in detail.
Results
: The aneurysmal volume (
V
), height (
H
), aspect ratio (
AR
), and spatial averaged, maximum, and minimum wall shear stress of the aneurysm dome normalized by the spatially averaged wall shear stress of the parent vessel (
NWSSave
,
NWSSmax
, and
NWSSmin
) were significantly altered between pre‐ and post‐rupture. In particular, the morphological parameters increased after the rupture (average
CR
of
V
,
H
, and
AR
were 25.8 %, 13.4 %, and 15.9 %, respectively). These results indicate that the aneurysm shapes tended to increase lengthwise after the rupture. On the other hand, the
NWSS
tended to decrease (average
CR
of
NWSSave
,
NWSSmax
, and
NWSSmin
were ‐21.0 %, ‐13.7 %, and ‐22.7 %, respectively). These results imply that the aneurysm rupture altered the aneurysm to a more complicated shape, and thereby the blood flow became stagnated that introduced lower
WSS
. In contrast, there were some cases in which
NWSS
increased, and these cases had vasospasm at their parent arteries caused by the rupture (i.e., 5 of 21 cases had vasospasm, and the average
CR
of
NWSSave
was 14.1 %). The parent vessel proximal to the aneurysm was shrunk due to the vasospasm, resulting in increased flow velocity and thus increased
NWSS
.
Conclusions
: The cerebral aneurysm rupture deformed the aneurysms into longitudinal and led to increased volumes. The NWSSs in CFD simulations using post‐rupture geometries tended to decrease in comparison with pre‐rupture. When studying rupture factors of cerebral aneurysms using geometrical measurements and CFD simulations, special attention should be paid to the clinical image and rupture characteristics standardization criteria.
Threshold Values of Morphological Parameters Associated with Cerebral Aneurysm Rupture Risk