A vertebrobasilar junction aneurysm successfully treated with a combination of surgical clipping and flow diverter placement based on the results of computational fluid dynamics analysis: illustrative case.

BACKGROUND: The treatment of vertebrobasilar junction (VBJ) aneurysms is challenging. Although flow diverters (FDs) are a possible treatment option, geometrical conditions hinder intervention. VBJ aneurysms possess dual inflow vessels from the bilateral vertebral arteries (VAs), one of which is ideally occluded prior to FD treatment. However, it remains unclear which VA should be occluded. OBSERVATIONS: A 75-year-old male with a growing VBJ complex aneurysm exhibiting invagination toward the brainstem and causing perifocal edema required intervention. Preoperative computational fluid dynamics (CFD) analysis demonstrated that left VA occlusion would result in more stagnant flow and less impingement of flow than right VA occlusion. According to the simulated strategy, surgical clipping of the left VA just proximal to the aneurysm was performed, followed by FD placement from the basilar artery trunk to the right VA. The patient demonstrated tolerance of the VA occlusion, and follow-up computed tomography angiography at 18 months after FD treatment confirmed the disappearance of the aneurysm. LESSONS: Preoperative flow dynamics simulations using CFD analysis can reveal an optimal treatment strategy involving a hybrid surgery that combines FD placement and direct surgical occlusion for a VBJ complex aneurysm.

Unilateral Approach for Bilateral Middle Cerebral Artery Aneurysms Assisted by Preoperative Understanding of Aneurysm Wall Properties: Two-Dimensional Operative Video.

Unruptured middle cerebral artery (MCA) aneurysms often exist bilaterally, and a unilateral approach for bilateral MCA aneurysms has been reported; however, this remains challenging because there are various technical nuances.1-4 Wall properties have been reported to be an important issue for this strategy.2,3 Atherosclerotic changes in the aneurysm wall can make clipping difficult. We present a video case demonstrating clipping of bilateral MCA aneurysms via a unilateral craniotomy assisted by preoperative understanding of the aneurysm wall properties using computational fluid dynamic analysis (Video 1). A 71-year-old woman had bilateral MCA bifurcation aneurysms. The oscillatory shear index color map by computational fluid dynamic analysis demonstrated that the contralateral MCA aneurysm did not have a high oscillatory shear index area in the dome, which means that there was no wall thickening, and the ipsilateral MCA aneurysm had scattered high oscillatory shear index areas, which were expected to have extreme wall thickening.5 After pterional craniotomy, the sylvian fissure was widely opened. As expected, the contralateral MCA aneurysm did not have a thick-walled region, enabling simple neck clipping using a straight clip. In contrast, the ipsilateral MCA aneurysm had thick-walled areas, as predicted, necessitating a multiple clip application. Postoperatively, the patient was discharged without any neurological deficits. Prediction of aneurysm wall properties using computational fluid dynamic analysis could assist in determining clippability of intracranial aneurysms, especially for aneurysms approached by narrow and deep surgical fields, such as contralateral MCA aneurysms. The patient consented to the procedure and the publication of their images.

Newly Identified Hemodynamic Parameter to Predict Thin-Walled Regions of Unruptured Cerebral Aneurysms Using Computational Fluid Dynamics Analysis.

BACKGROUND: The thin-walled regions (TIWRs) of intracranial aneurysms have a high risk of rupture during surgical manipulation. They have been reported to be predicted by wall shear stress and pressure (PS) based on computational fluid dynamics analysis, although this remains controversial. In this study, we investigated whether the oscillatory shear index (OSI) can predict TIWRs. METHODS: Twenty-five unruptured aneurysms were retrospectively analyzed; the position and orientation of the computational fluid dynamics color maps were adjusted to match the intraoperative micrographs. The red area on the aneurysm wall was defined as TIWR, and if most of the regions on the color map corresponding to TIWR were OSI low (lower quartile range), time-averaged wall shear stress (TAWSS) high, or PS high (upper quartile range), each region was defined as a matched region and divided by the total number of TIWRs to calculate the match rate. In addition, the mean values of OSI, TAWSS, and PS corresponding to TIWRs were quantitatively compared with those in adjacent thick-walled regions. RESULTS: Among 27 TIWRs of 25 aneurysms, 23, 10, and 14 regions had low OSI, high TAWSS, and high PS regions (match rate: 85.2%, 37.0%, and 51.9%), respectively. Receiver operating characteristic curve analysis demonstrated that OSI was the most effective hemodynamic parameter (area under the curve, 0.881), followed by TAWSS (0.798). Multivariate analysis showed that OSI was a significant independent predictor of TIWRs (odds ratio, 18.30 [95% CI, 3.2800-102.00], P < 0.001). CONCLUSIONS: OSI may be a unique predictor for TIWRs. Low OSI strongly corresponds with TIWRs of intracranial aneurysms.

Clear Detection of Thin-Walled Regions in Unruptured Cerebral Aneurysms by Using Computational Fluid Dynamics.

OBJECTIVE: Thin-walled regions (TIWRs) within cerebral aneurysms have a high risk of rupture during surgical manipulation. Previous reports have demonstrated specific changes in the parameters of computational fluid dynamics in TIWRs; however, they have not been fully evaluated. We identified and investigated a novel parameter, wall shear stress vector cycle variation (WSSVV), with user-friendly software that could predict TIWRs. METHODS: Twelve unruptured cerebral aneurysms were analyzed. TIWRs were defined as reddish areas compared with the normal-colored parent artery on intraoperative views. The position and orientation of these clinical images were adjusted to match the WSSVV color maps. TIWRs and thick-walled regions (TKWRs) were marked and compared with the corresponding regions on WSSVV maps. The default images obtained from WSSVV imaging required appropriate maximum color bar value (MCBV) adjustment for predicting TIWRs. Sensitivity and specificity analyses were performed by changing the MCBV from 300 to 700 at intervals of 100. With the optimal MCBV, the WSSVV values were quantitatively compared. RESULTS: All of the selected 18 TIWRs and 16 TKWRs corresponded to low- and high-value regions of the WSSVV color maps at the adjusted MCBV, respectively. The mean optimal MCBV was 483.3 ± 167.50 (range, 300-700). According to receiver operating characteristic analysis, the best MCBV for predicting TIWRs was 500 (highest sensitivity, 0.89; specificity, 0.94). Under this condition, the quantitative values of the computational fluid dynamics color maps for TIWRs and TKWRs were significantly different (P < 0.01). CONCLUSIONS: Low WSSVV values may indicate TIWRs within cerebral aneurysms.

Detection of Hemodynamic Characteristics Before Growth in Growing Cerebral Aneurysms by Analyzing Time-of-Flight Magnetic Resonance Angiography Images Alone: Preliminary Results.

OBJECTIVE: Cerebral aneurysm growth often precedes rupture. Definite contributors to aneurysm growth have not been determined even by means of recently developed commercially available computational fluid dynamics (CFD) software. We developed an original CFD tool that can analyze data from time-of-flight magnetic resonance angiography (TOF-MRA) before growth in the growing aneurysms and investigate possible factors for aneurysm growth in the near future. METHODS: We retrospectively reviewed unruptured aneurysms that were treated at our institute because of aneurysm growth (growing group) between April 2013 and March 2017. Stable aneurysms that had demonstrated no growth for more than 5 years were selected (stable group). TOF-MRA data of these aneurysms were retrospectively converted to 3-dimensional vessel geometric data; 3 hemodynamic indices including streamline, wall shear stress (WSS), and oscillatory shear index were calculated by our original CFD tool using the lattice Boltzmann method to quantitatively compare the 2 groups. RESULTS: Six growing aneurysms and 6 stable aneurysms were analyzed. Of the 6 growing aneurysms, WSS on the focal aneurysmal sac increased temporally in the vicinity of the constant low WSS area at the peak systolic phase. By contrast, WSS did not increase during any part of the cardiac cycle in 3 of the 6 stable aneurysms. The peak values of WSS were significantly different between the 2 groups. CONCLUSIONS: A focal increase in WSS in the peak systolic phase may be a risk factor for aneurysm enlargement in the near future.

Implicit-correction-based immersed boundary-lattice Boltzmann method with two relaxation times.

In the present paper, we verify the effectiveness of the two-relaxation-time (TRT) collision operator in reducing boundary slip computed by the immersed boundary-lattice Boltzmann method (IB-LBM). In the linear collision operator of the TRT, we decompose the distribution function into symmetric and antisymmetric components and define the relaxation parameters for each part. The Chapman-Enskog expansion indicates that one relaxation time for the symmetric component is related to the kinematic viscosity. Rigorous analysis of the symmetric shear flows reveals that the relaxation time for the antisymmetric part controls the velocity gradient, the boundary velocity, and the boundary slip velocity computed by the IB-LBM. Simulation of the symmetric shear flows, the symmetric Poiseuille flows, and the cylindrical Couette flows indicates that the profiles of the numerical velocity calculated by the TRT collision operator under the IB-LBM framework exactly agree with those of the multirelaxation time (MRT). The TRT is as effective in removing the boundary slip as the MRT. We demonstrate analytically and numerically that the error of the boundary velocity is caused by the smoothing technique using the δ function used in the interpolation method. In the simulation of the flow past a circular cylinder, the IB-LBM based on the implicit correction method with the TRT succeeds in preventing the flow penetration through the solid surface as well as unphysical velocity distortion. The drag coefficient, the wake length, and the separation points calculated by the present IB-LBM agree well with previous studies at Re = 10, 20, and 40.