Bulang Gao

Aneurysm Inflow-Angle as a Discriminant for Rupture in Sidewall Cerebral Aneurysms Morphometric and Computational Fluid Dynamic Analysis

Background and Purpose— The ability to discriminate between ruptured and unruptured cerebral aneurysms on a morphological basis may be useful in clinical risk stratification. The objective was to evaluate the importance of inflow-angle (IA), the angle separating parent vessel and aneurysm dome main axes. Methods— IA, maximal dimension, height–width ratio, and dome–neck aspect ratio were evaluated in sidewall-type aneurysms with respect to rupture status in a cohort of 116 aneurysms in 102 patients. Computational fluid dynamic analysis was performed in an idealized model with variational analysis of the effect of IA on intra-aneurysmal hemodynamics. Results— Univariate analysis identified IA as significantly more obtuse in the ruptured subset (124.9°±26.5° versus 105.8°±18.5°, P=0.0001); similarly, maximal dimension, height–width ratio, and dome–neck aspect ratio were significantly greater in the ruptured subset; multivariate logistic regression identified only IA (P=0.0158) and height–width ratio (P=0.0017), but not maximal dimension or dome–neck aspect ratio, as independent discriminants of rupture status. Computational fluid dynamic analysis showed increasing IA leading to deeper migration of the flow recirculation zone into the aneurysm with higher peak flow velocities and a greater transmission of kinetic energy into the distal portion of the dome. Increasing IA resulted in higher inflow velocity and greater wall shear stress magnitude and spatial gradients in both the inflow zone and dome. Conclusions— Inflow-angle is a significant discriminant of rupture status in sidewall-type aneurysms and is associated with higher energy transmission to the dome. These results support inclusion of IA in future prospective aneurysm rupture risk assessment trials.

Stent-Assisted Coiling of Intracranial Bifurcation Aneurysms Leads to Immediate and Delayed Intracranial Vascular Angle Remodeling

BACKGROUND AND PURPOSE: Wide-neck bifurcating aneurysms are increasingly treated with intracranial stent-assisted coiling by using shape-memory alloy microstents. We sought to investigate the short- and long-term effects of intracranial stent implantation on the geometry and angular conformation of the stent-coiled vascular bifurcation. MATERIALS AND METHODS: Thirty patients underwent stent-mediated coiling for 31 bifurcation aneurysms by using 31 self-expanding Neuroform (n = 14) and Enterprise (n = 17) stents (17 women; mean age, 56 years). The angle (δ) between the stented mother and daughter vessels at the bifurcation was measured by using multiplanar imaging of reconstructed rotational conventional angiography volumes and was compared by using matched-pair statistics. Neuroform and Enterprise longitudinal stent stiffness was measured in vitro at an increasing bending angle θ (θ = 180°− δ). RESULTS: Stent deployment increased the bifurcation angle δ from 101.5° to 119.8° postprocedurally and to 137.3° (P < .0001) at latest follow-up, resulting in effective straightening; the angular remodeling was greater in distal-versus-proximal arteries (anterior cerebral > MCA > BA > ICA), inversely proportional to mother-vessel diameter and proportional to pretreatment bending angle θ. At follow-up, angle δ continued to significantly expand, with remodeling being greater in the early period (1–6 versus >7 months) and more pronounced with the longitudinally stiffer closed-cell Enterprise compared with the open-cell Neuroform stent. CONCLUSIONS: Stent placement across bifurcation aneurysms leads to a significant biphasic angular remodeling related to stent type and vessel caliber, altering morphology to mimic sidewall lesions, a phenomenon needing consideration during procedural planning. Future work is needed to uncover the hemodynamic implications of this structural change and any possible effect on aneurysm-recurrence rates.

Identification of a dichotomy in morphological predictors of rupture status between sidewall- and bifurcation-type intracranial aneurysms.

OBJECT Prediction of aneurysm rupture likelihood is clinically valuable, given that more unruptured aneurysms are being discovered incidentally with the increased use of imaging. The authors set out to evaluate the relative performance of morphological features for rupture status discrimination in the context of the divergent geometrical and hemodynamic characteristics of sidewall- and bifurcation-type aneurysms. METHODS Catheter 3D rotational angiographic images of 271 consecutive aneurysms (101 ruptured, 135 bifurcation type) were used to assess the following parameters in 3D: maximum diameter (D(max)), height, height/width ratio, aspect ratio, size ratio, nonsphericity index, and inflow angle. Univariate statistics applied to the bifurcation, sidewall, and combined (bifurcation + sidewall) sets identified significant features for inclusion in multivariate analysis yielding area under the curve (AUC) and optimal thresholds in the receiver-operating characteristic. Furthermore, a computational fluid dynamics analysis was performed to evaluate the flow and wall shear stress conditions inside sidewall and bifurcation aneurysms at different inflow angles. RESULTS The mean D(max), height, and inflow angle were significantly greater in ruptured sidewall aneurysms than in unruptured sidewall aneurysms, but showed no difference between ruptured and unruptured bifurcation lesions. There was a statistically significant difference between ruptured and unruptured aneurysms for all measured features in the combined set. Multivariate analysis identified the following: 1) nonsphericity index as the only rupture status discriminator in bifurcation lesions (AUC = 0.67); 2) height/width ratio, size ratio, and inflow angle as strong discriminators in sidewall lesions (AUC = 0.87); and 3) height/width ratio, inflow angle, and size ratio as intermediate discriminators in the combined group (AUC = 0.76). Computational fluid dynamics analysis showed that although increasing inflow angle in a sidewall model led to deeper penetration of flow, higher velocities, and higher wall shear stress inside the aneurysm dome, it produced the exact opposite results in a bifurcation model. CONCLUSIONS Retrospective morphological and hemodynamic analysis point to a dichotomy between sidewall and bifurcation aneurysms with respect to performance of shape and size parameters in identifying rupture status, suggesting the need for aneurysm type-based analyses in future studies. The current most commonly used clinical risk assessment metric, D(max), was found to be of no value in differentiating between ruptured and unruptured bifurcation aneurysms.

Y-stent coiling of basilar bifurcation aneurysms induces a dynamic angular vascular remodeling with alteration of the apical wall shear stress pattern.

BACKGROUND Although wide-necked basilar bifurcation aneurysms are treated with Y-stent coiling, the effect of this intervention on vessel configuration and hemodynamics is unknown. OBJECTIVE To investigate the immediate and delayed effects of Y-stenting using self-expanding microstents on basilar bifurcation architecture and hemodynamics. METHODS Fifteen patients underwent basilar Y-stent coiling and imaging with rotational angiography. Vascular angles were measured between proximal P1 segments of the posterior cerebral arteries (α) and between the basilar artery and each P1 segment (β(1,2)) in the anteroposterior and γ(1,2) sagittal planes. Patient-specific computational fluid dynamic analysis was used to estimate wall shear stress (WSS) changes with treatment. RESULTS In the anteroposterior plane, Y-stenting significantly decreased angle α and increased β angles immediately after stent coiling (P < .05 and P < .01, respectively) in a continued dynamic remodeling that progressed further in later months; sagittal γ angles also decreased (P < .0001). This novel stent-induced geometric progressive remodeling resulted in effective straightening and narrowing of the basilar bifurcation angle α (150.0 degrees vs 113 degrees, P < .0001) with significant correlation (r = 0.39, P < .05) between pretreatment proximal P1 angles and maximal angular change. Computational fluid dynamic analysis showed the angular remodeling led to significant narrowing of the WSS interpeak at the apex, redirecting high WSS away from the neck transition zone with native vessel toward the inert coil mass. CONCLUSION Y-configuration stent coiling induced immediate and, more significantly, a previously undefined delayed cerebrovascular remodeling. This progressive stent-induced angular remodeling alters perianeurysmal hemodynamics, independent of the flow-diverting properties of stent struts, thus shifting the balance of hemodynamic forces affecting aneurysm development and evolution.

Angular remodeling in single stent-assisted coiling displaces and attenuates the flow impingement zone at the neck of intracranial bifurcation aneurysms.

BACKGROUND Self-expanding intracranial stent-assisted coiling of bifurcation aneurysms has recently been shown to straighten target cerebral vessels, a phenomenon with unknown hemodynamic effect. OBJECTIVE To investigate the impact of angular remodeling in aneurysms treated with single stent-assisted coiling with the use of computational fluid dynamic techniques. METHODS Fourteen patients (7 women, mean age 55) who underwent stent coiling of 14 wide-necked bifurcation aneurysms were included based on the availability of high-resolution 3-dimensional rotational angiography. Pretreatment data sets underwent virtual aneurysm removal to isolate the effect of stenting. Wall shear stress and pressure profiles obtained from constant flow input computational fluid dynamic analysis were analyzed for apical hemodynamic changes. RESULTS Stenting increased the bifurcation angle with significant straightening immediately after treatment and at follow-up (107.3° vs. 144.9°, P < .001). The increased stented angle at follow-up led to decreased pressure drop at the bifurcation apex (12.2 vs. 9.9 Pa, P < .003) and migration of the flow impingement zone (FIZ) toward the contralateral nonstented daughter branch by a mean of 1.48 ± 0.2 mm. Stent-induced angular remodeling decreased FIZ width separating peak apical wall shear stress (3.4 vs. 2.5 mm, P < .004). Analysis of FIZ distance measured from the parent vessel centerline showed it to be linearly (r = .58, P < .002) and FIZ width inversely correlated (r = .46, P < .02) to vessel bifurcation angle. CONCLUSION Stent-induced angular remodeling significantly altered bifurcation apex hemodynamics in a favorable direction by blunting apical pressure and inducing the narrowing and migration of the FIZ, a novel response to intracranial stenting that should be added to intimal hyperplasia and flow diversion.

Possible mechanisms for delayed migration of the closed cell--designed enterprise stent when used in the adjunctive treatment of a basilar artery aneurysm.

With great interest, we read the 2 articles documenting delayed migration of the self-expanding intracranial microstent—the Enterprise (Cordis, Miami Lakes, Florida).[1][1],[2][2] Meanwhile, Lavine et al[3][3] had recorded another delayed migration of the Enterprise stent their article in

Incremental Contribution of Size Ratio as a Discriminant for Rupture Status in Cerebral Aneurysms: Comparison With Size, Height, and Vessel Diameter

BACKGROUND: Aneurysm size ratio (SR), variably defined as the ratio of dome height (H) or maximal dimension (Dmax) over average parent vessel diameter (PV) diameter, has been proposed as a promising aneurysm rupture status predictor. OBJECTIVE: To evaluate the incremental contribution of SR to retrospective rupture status determination in a large high-resolution aneurysm database. METHODS: Measurements were performed on catheter 3D-rotational angiographic volumetric datasets for 267 aneurysms (98 ruptured). SR was computed both as H/PV (SR1) and as Dmax/PV (SR2), and its discriminant performance was evaluated on the whole dataset, on aneurysm-type subsets (bifurcation [BIF] vs sidewall [SW]), and at specific aneurysm locations. Univariate and multivariate statistical analyses were performed by the use of area under the curve (AUC) of the receiver-operating characteristics. RESULTS: Neither SR1 nor SR2 were statistically correlated to rupture status in the BIF group, where only PV (AUC = 0.61) achieved significance. All parameters were statistically significant in the combined group, but with modest performance (AUC range, 0.62-0.74). SR1 (AUC = 0.84) and SR2 (AUC = 0.78) were strong predictors in the SW group, similar to H (AUC = 0.83) and Dmax (AUC = 0.77). Multivariate statistics failed to support SR as an incremental independent parameter from PV, Dmax, and H. CONCLUSION: SR provides an uneven performance that depends strongly on the BIF/SW distribution of the data and is not useful for bifurcation lesions. In the SW subset, the incremental contribution of the SR over its H or Dmax individual component measurements could not be validated, suggesting prior findings of its utility to be the result of aneurysm-type selection bias.

Widening of the basilar bifurcation angle: association with presence of intracranial aneurysm, age, and female sex

OBJECT Arterial bifurcations represent preferred locations for aneurysm formation, especially when they are associated with variations in divider geometry. The authors hypothesized a link between basilar apex aneurysms and basilar bifurcation (α) and vertebrobasilar junction (VBJ) angles. METHODS The α and VBJ angles were measured in 3D MR and rotational angiographic volumes using a coplanar 3-point technique. Angle α was compared between age-matched cohorts in 45 patients with basilar artery (BA) aneurysms, 65 patients with aneurysms in other locations (non-BA), and 103 nonaneurysmal controls. Additional analysis was performed in 273 nonaneurysmal controls. Computational fluid dynamics (CFD) simulations were performed on parametric BA models with increasing angles. RESULTS Angle α was significantly wider in patients with BA aneurysms (146.7° ± 20.5°) than in those with non-BA aneurysms (111.7° ± 18°) and in controls (103° ± 20.6°) (p < 0.0001), whereas no difference was observed for the VBJ angle. A wider angle α correlated with BA aneurysm neck width but not dome size, which is consistent with CFD results showing a widening of the impingement zone at the bifurcation apex. BA bifurcations hosting even small aneurysms (< 5 mm) had a significantly larger α angle compared with matched controls (p < 0.0001). In nonaneurysmal controls, α increased with age (p < 0.0001), with a threshold effect above 35 years of age and a steeper dependence in females (p = 0.002) than males (p = 0.04). CONCLUSIONS The α angle widens with age during adulthood, especially in females. This angular widening is associated with basilar bifurcation aneurysms and may predispose individuals to aneurysm initiation by diffusing the flow impingement zone away from the protective medial band region of the flow divider.

Enterprise stenting for intracranial aneurysm treatment induces dynamic and reversible age-dependent stenosis in cerebral arteries

Background Although intracranial stenting has been associated with in-stent stenosis, the vascular response of cerebral vessels to the deployment of the Enterprise vascular reconstruction device is poorly defined. Objective To evaluate the change in parent vessel caliber that ensues after Enterprise stent placement. Methods Seventy-seven patients with 88 aneurysms were treated using Enterprise stent-assisted coil embolization and underwent high-resolution three-dimensional rotational angiography followed by three-dimensional edge-detection filtering to remove windowing-dependence measurement artifact. Orthogonal diameters and cross-sectional areas (CSAs) were measured proximal and distal on either side of the leading stent edge (points A, B), trailing stent edge (points D, E), and at mid-stent (point C). Results Enterprise stent deployment caused an instant increase in the parent artery CSA by 8.98% at D, which was followed 4–6 months later by significant in-stent stenosis (15.78% at A, 27.24% at B, 10.68% at C, 32.12% at D, and 28.28% at E) in the stented artery. This time-dependent phenomenon showed resolution which was complete by 12–24 months after treatment. This target vessel stenosis showed significant age dependence with greater response in the young. No flow-limiting stenosis requiring treatment was observed in this series. Conclusions Use of the Enterprise stent is associated with a significant dynamic and spontaneously resolvable age-dependent in-stent stenosis. Further study is warranted on the clinical impact, if any, of this occurrence.

Stent recanalization of carotid tonsillar loop dissection using the Enterprise vascular reconstruction device

Although advances in endovascular techniques have permitted reconstruction of intimal dissections and related pseudoaneurysms of the extracranial cervical internal carotid artery, highly tortuous tonsillar loop anatomic variants still pose an obstacle to conventional extracranial self-expanding carotid stents. During a 12 year period, nine of 48 cases with cervical carotid dissections were associated with a tonsillar loop. Five patients required endovascular treatment, which was performed using a microcatheter-based technique with the low-profile Enterprise vascular reconstruction device (Codman Neurovascular, Raynham, MA, USA). Technical, radiographic, and clinical outcomes were analyzed for each patient. Dissection etiology was spontaneous in three patients, iatrogenic in one, and traumatic in one. Four near-occlusive tonsillar loop dissections were successfully recanalized during the acute phase. Dissection-related stenosis improved from 90±22% to 31±13%, with tandem stents needed in three instances to seal the inflow zone. There were no procedure-related transient ischemic attacks (TIA), minor/major strokes, or deaths. Angiographic follow-up for a mean of 28.0±21.6 months showed all stents were patent, with average stenosis of 25.2±12.2%. Focal ovalization and kinking of the closed-cell design was noted at the sharpest curve in one patient. Clinical outcome (follow-up of 28.1±21.5 months) demonstrated overall improvement with no clinical worsening, new TIA, or stroke. Tonsillar loop-associated carotid dissections can be successfully and durably recanalized using the low-profile Enterprise stent with an excellent long-term patency rate and low procedural risk. The possibility of stent kinking and low radial force should be considered when planning reconstruction with this device.