Contribution of the hemodynamics of A1 dysplasia or hypoplasia to anterior communicating artery aneurysms: a 3-dimensional numerical simulation study

An assessment of how the anterior cerebral artery anatomy impacts ACoA aneurysm formation based on CFD analysis

OBJECTIVE

The aim of this study was to identify independent anatomic, morphologic and hemodynamic features of the ACoA (anterior communicating artery) complex that serve as risk factors for the occurrence of ACoA aneurysms.

METHODS

Fifteen consecutive patients with 15 ACoA aneurysms were included. Computational fluid dynamics (CFD) simulations based on patient-specific models were carried out using 3D time-of-flight magnetic resonance angiography (3D-TOF-MRA) images. A reverse reconstruction technique was used to generate a pre-aneurysm vessel anatomy. Geometric parameters and hemodynamic changes were compared and evaluated.

RESULTS

The overall prevalence of symmetric, dysplastic, and absent A1 segments were 53.3%, 26.7%, and 20%. The mean wall shear stress (WSS) of the absent group (AG) was significantly higher than that of the symmetric group (SG) and dysplastic group (DG). The absolute mean A1 artery flow rate (410.2 ± 88 versus 439.4 ± 101 mL/min; p = .45) of the aneurysm side was similar between the SG and DG but significantly higher in the AG (528.1 ± 77 mL/min; p < .05). The A1-A2 angles of the aneurysm side showed no significant differences among the 3 groups (p = .32). However, the mean A1-A2 angle on the aneurysm side was smaller than the contralateral A1-A2 angle (101.9 ± 9.1˚ versus 120.3 ± 7.7˚; p <.05). A regression analysis demonstrated that high WSS was significantly associated with a large A1-A2 ratio (R2=0.52; p <.05).

CONCLUSIONS

ACoA aneurysms are a high-WSS pathology. Severe flow impingement and the anatomic vasculature structures play a role in triggering the occurrence of ACoA aneurysms.

Morphometry of cerebral arterial bifurcations harbouring aneurysms: a case-control study

Background

Conclusions from studies evaluating vessel dimensions and their deviations from values resulting from the principle of minimum work (PMW) on the formation of intracranial aneurysms (IAs) are still inconclusive. Our study aimed to perform a morphometric analysis of cerebral arterial bifurcations harbouring aneurysms.

Methods

The study comprised 147 patients with basilar artery (BA) and middle cerebral artery (MCA) aneurysms and 106 patients constituting the control group. The following morphometric parameters were evaluated: the radii of vessels forming the bifurcation, the junction exponent, the values of the bifurcation angles (Φ₁ and Φ₂ angles between the parent vessel trunk axis and the larger or smaller branches, respectively; α angle, the total bifurcation angle) and the difference between the predicted optimal and observed branch angles.

Results

The analysed parameters for internal carotid artery (ICA) bifurcations were not significantly different among the groups. The MCA and BA bifurcation angles and the radii of the parent MCA and BA vessels with aneurysms were significantly higher than those of the control group. The differences between the predicted optimal and observed branch angles were significantly higher for BA and MCA bifurcations with aneurysms compared to the control group. The mean junction exponent for bifurcations in the circle of Willis (i.e., ICA and BA bifurcations, respectively) and MCA bifurcations with aneurysms was significantly lower than the theoretical optimum and did not significantly differ among the groups. In a multilevel multivariate logistic regression analysis, the branch angles and the radius from the parent vessel were significant independent predictors of the presence of an IA. The ROC analysis indicated that the α angle was the best performer in discriminating between aneurysmal and nonaneurysmal bifurcations.

Conclusions

The dimensions of the arteries forming the circle of Willis do not follow the PMW. Deviation from the energetically optimum geometry for bifurcations beyond the circle of Willis (particularly, a larger radius of the parent artery and a wider total bifurcation angle) may lead to the formation of IAs. Further studies are warranted to investigate the significance of vessel dimensions and the bifurcation angle on the magnitude of shear stress in the walls of arterial bifurcations.

Vascular Geometry Associated with Anterior Communicating Artery Aneurysm Formation

OBJECTIVE

To identify clinical and morphologic risk factors correlated with anterior communicating artery (ACoA) aneurysm formation.

METHODS

Three-dimensional morphologic parameters obtained from computed tomography angiography or digital subtraction angiography from 504 patients with ACoA aneurysms and 201 patients with aneurysms in other locations that were diagnosed at Brigham and Women's Hospital and Massachusetts General Hospital between 1990 and 2016 were evaluated. The presence of hypoplastic and aplastic A1 segments and diameters and angles of surrounding parent and daughter vessels were examined. Univariable and multivariable statistical analyses were performed to determine statistical significance. Sensitivity analyses for small (≤3 mm) aneurysms only were also performed.

RESULTS

Aplastic and hypoplastic A1 segments were more common in the ACoA group (38.9% vs. 6.5% hypoplastic and 22.2% vs. 0.5% aplastic). In multivariable analysis, the presence of a hypoplastic A1 segment was associated with ACoA aneurysms. An A2-ACoA (daughter-daughter) angle was also significantly associated with ACoA aneurysms in multivariable analysis; however, as Pearson's correlation test between aneurysm width and daughter-daughter angle was significant, the daughter-daughter angle was most likely not independently associated with aneurysm presence, but rather might have been a result of the presence of an aneurysm. Subgroup analyses of small aneurysms (≤3 mm) and of unruptured aneurysms showed similar results.

CONCLUSIONS

Our results demonstrate that of all the morphologic parameters, the presence of a hypoplastic A1 segment was the only parameter independently associated with the presence of ACoA aneurysms that was not correlated with aneurysm size and could aid as a simple screening parameter.

Morphological risk model assessing anterior communicating artery aneurysm rupture: Development and validation

OBJECTIVE

Prediction of the rupture risk in anterior communicating artery (ACoA) aneurysms remains challenging. We aimed to investigate the association of detailed morphologies with ACoA aneurysm rupture.

PATIENT AND METHODS

759 consecutive patients with ACoA aneurysms were identified from December 2007 to January 2016. An independent cohort was collected for validation from March 2017 to October 2019. Morphological parameters of the aneurysms were measured using CT angiography. Univariable and multivariable analyses were used to investigate the association of morphological characteristics with aneurysm rupture. Area under receiver operating characteristic curves (AUC) were used to assess the performance of the model.

RESULTS

A total of 650 patients with 650 ACoA aneurysms were included for the derivation, and 41 patients with 41 ACoA aneurysms were included for the validation. Aneurysm size, neck size, aspect ratio, size ratio, vessel angle, anterior projection, dominant A1 segment, irregular shape, the presence of a daughter dome, vessel size, and aneurysm angle were risk factors for rupture. The multivariable analysis showed that a larger aneurysm, anterior projection of aneurysms, dominant A1 segment, and irregular aneurysms were associated with aneurysm rupture, whereas larger vessel size was inversely associated with rupture. The morphological risk score showed good discrimination of ruptured and unruptured aneurysms with an AUC of 0.73 in the derivation and an AUC of 0.80 in the validation, and good calibration in both cohorts, signifying a good fit.

CONCLUSION

The morphological risk model may contribute to evaluating the risk of rupture of ACoA aneurysms.

Morphological Variables Associated With Ruptured Middle Cerebral Artery Aneurysms

BACKGROUND

Geometric factors of intracranial aneurysms and surrounding vasculature could affect the risk of aneurysm rupture. However, large-scale assessments of morphological parameters correlated with intracranial aneurysm rupture in a location-specific manner are scarce.

OBJECTIVE

To investigate the morphological characteristics associated with ruptured middle cerebral artery (MCA) aneurysms.

METHODS

Five hundred sixty-one patients with 638 MCA aneurysms diagnosed between 1990 and 2016 who had available computed tomography angiography (CTA) were included in this study. CTAs were evaluated using the Vitrea Advanced Visualization software for 3-dimensional (3D) reconstruction. Morphological parameters examined in each model included aneurysm projection, wall irregularity, presence of a daughter dome, presence of hypoplastic or aplastic A1 arteries and hypoplastic or fetal posterior communicating arteries (PCoA), aneurysm height and width, neck diameter, bottleneck factor, aspect and size ratio, height/width ratio, and diameters and angles of surrounding parent and daughter vessels. Univariable and multivariable statistical analyses were performed to determine the association of morphological characteristics with rupture of MCA aneurysms. Logistic regression was used to build a predictive MCA score.

RESULTS

Greater bottleneck and size ratio, and irregular, multilobed, temporally projecting MCA aneurysms are associated with higher rupture risk, whereas higher M1/M2 ratio, larger width, and the presence of an ipsilateral or bilateral hypoplastic PCoA were inversely associated with rupture. The MCA score had good predictive capacity with area under the receiver operating curve = 0.88.

CONCLUSION

These practical morphological parameters specific to MCA aneurysms are easy to assess when examining 3D reconstructions of unruptured aneurysms and could aid in risk evaluation in these patients.

Cerebral Aneurysms: Are They Associated with Anatomic Variations of Carotid and Main Cerebral Arteries?

OBJECTIVE

Vascular anatomic variations are very common in the population, but their coexistence with life-threating vascular malformations remains unclear. The objective of the study was to assess the correlation between the presence of anatomic variants of both carotid and main cerebral arteries and the occurrence of cerebral aneurysms.

METHODS

We analyzed examinations of 194 patients who underwent computed tomography angiography of the head and neck between September of 2016 and November of 2017. The assessed parameters were: the variation of the common carotid arteries origin, hypoplasia or duplication of any of the main cerebral arteries, carotid artery kinking, and the presence of cerebral aneurysms.

RESULTS

We found 5.7% of patients had a cerebral aneurysm. Hypoplasia of at least 1 main cerebral artery occurred in 34.5% of patients, with the most frequent being the vertebral artery (21.6%). Duplication of at least 1 main cerebral artery was detected in 2.6%. Cerebral aneurysms occurred more often together with hypoplasia (P = 0.041; OR = 3.175) or duplication (P < 0.001; OR = 18.500) of at least 1 main cerebral artery. In 7.2% of cases, the origin of common carotid arteries created a true bovine arch, and in 4.1% the so-called bovine arch. Patients with alternative variants of aortic arch branching were more likely to have cerebral aneurysms (P = 0.002; OR = 5.903). We found 27.3% of patients had internal carotid arteries affected by kinking. Carotid kinking did not predispose the patient to the formation of a cerebral aneurysm (P = 0.378).

CONCLUSIONS

There is an evident correspondence between the presence of vascular anatomic variants (abnormal origin of the carotid arteries, hypoplasia, or duplication of the main cerebral artery) and the occurrence of cerebral aneurysms.

Aneurysms of the Proximal (A1) Segment of the Anterior Cerebral Artery: A Clinical Analysis of 31 Cases

OBJECTIVE

This study aimed to investigate the characteristics of A1 aneurysms according to their locations and to compare their imaging appearances so as to identify factors associated with their rupture.

METHODS

We retrospectively reviewed the medical records of 31 patients harboring 32 A1 aneurysms diagnosed and treated between March 2009 and September 2018 at our institute.

RESULTS

Thirteen (41.9%) of the patients had vascular abnormalities, and multiple aneurysms were found in 13 (41.9%) patients. A total of 16 (53.3%) aneurysms were located on the proximal A1 segment, whereas the middle segments were affected in 7 (23.3%) and the distal segments in 7 (23.3%). Altogether, 93.8% of proximal A1 aneurysms projected posteriorly, 85.7% of middle aneurysms projected superiorly, and 85.7% of distal aneurysms projected inferiorly (P = 0.000). Four (33.3%) of the 12 total ruptured aneurysms were located on the distal A1 segment. Nine (69.2%) ruptured aneurysms were elongated or irregular in shape (P = 0.004). The aspect and height-width ratios of the ruptured aneurysms were higher than those of the unruptured aneurysms (P = 0.001, P = 0.018, respectively).

CONCLUSIONS

Most A1 aneurysms showed a directional predilection according to the location of the A1 segment. Additionally, A1 aneurysms with elongated or irregular shapes, high aspect or height-width ratios, and distal locations of the A1 segment showed high risks of rupture. Therefore, a thorough assessment of the characteristics of A1 aneurysms can enhance the selection of proper treatment strategies.

Long-Term Effects of the Abdominal Aortic Aneurysm Model in Rabbits Prepared by Pancreatic Elastase Combined With Angiotensin II

OBJECTIVE:

This study aimed to observe the effect of pancreatic elastase combined with angiotensin II on a stable rabbit abdominal aortic aneurysm model.

METHODS:

A total of 20 male New Zealand rabbits were randomly divided into groups A and B, with 10 rabbits per group. The rabbits in group A were given an intraperitoneal perfusion of pancreatic elastase, and the rabbits in group B were given continuous pumping of angiotensin II in addition to the operation of group A. Before the operation and at 2, 4, and 16 weeks postoperation, vascular color Doppler ultrasonography was performed, and blood samples were collected to measure the serum matrix metalloproteinase 9 (MMP9) and MMP2 levels. At 16 weeks postoperation, all rabbits in both groups were killed, and hematoxylin and eosin, Elastic-van-Gieson, Masson's, and immunohistochemical staining were performed for the vessel specimens.

RESULTS:

At 2 weeks postoperation, the aneurysm formation rates of the 2 groups were both 100%, and the average expansion rates of the aneurysm diameters were 85% and 93%, respectively; these differences were not significant ( P = .150 and P = .280, respectively). At 4 weeks postoperation, the aneurysm formation rates of the 2 groups were 71.4% and 100%, and the average expansion rates of the aneurysm diameter were 68% and 99%, respectively; the differences between the groups were significant ( P = .031 and P = .022, respectively). At 16 weeks postoperation, the aneurysm formation rates of the 2 groups were 14.3% and 100%, and the average expansion rates of the aneurysm diameter were 12% and 108%, respectively; the differences between the groups were significant ( P = .026 and P = .014, respectively).

CONCLUSION:

Compared to the abdominal aortic aneurysm modeling method in rabbits based on pancreatic elastase alone, the abdominal aortic aneurysm modeling method in rabbits using pancreatic elastase combined with angiotensin II maintained the morphology of the abdominal aortic aneurysm for a longer time, showing an important application value for the long-term observation of changes in abdominal aortic aneurysms.

Small versus Large Ruptured Intracranial Aneurysm: Concerns with the Site of Aneurysm

Background: Although size is one of the strongest predictors, small aneurysms often rupture. We compared the characteristics of small and large ruptured intracranial aneurysms (RIAs) according to their location to find the factors associated with small RIAs in each location. Methods: Patients with subarachnoid hemorrhage due to saccular RIAs were consecutively enrolled. The sizes were dichotomized as small (<5 mm) or large, and the location was classified as paraclinoid-distal internal carotid artery, sidewalls of anterior or middle cerebral artery (MCA; sidewall), MCA-bifurcation, anterior or posterior communicating artery (Acom or Pcom, respectively), and posterior circulation RIAs. Independent factors associated with small RIAs compared to large RIAs were investigated in each location. Results: Small RIAs were observed in 384 of 791 patients (48.5%), and were most commonly located at Acom (17.1%) followed by Pcom (9.0%) and sidewalls (7.2%). Female sex (OR 3.038; 95% CI 2.099-4.395), young age (OR 0.971; 95% CI 0.958-0.985), hypertension (OR 1.412; 95% CI 1.033-1.930) and multiple aneurysms (OR 1.942; 95% CI 1.335-2.824) were associated with small RIAs. By location, sidewall aneurysms (OR 2.183; 95% CI 1.049-4.542) were associated with small RIAs, whereas MCA-bifurcation (OR 0.318; 95% CI 0.168-0.599) and Pcom aneurysms (OR 0.511; 95% CI 0.277-0.944) were associated with large RIAs. The presence of multiple aneurysms (OR 4.69; 95% CI 1.45-21.19) was associated with small RIAs at sidewalls, and young age, female sex, hypertension and the presence of bilateral A1 (OR 1.85; 95% CI 1.09-3.13) were associated with small RIAs at Acom. Acom RIAs with bilateral A1 was smaller than those with unilateral A1 (4.7 ± 2.1 vs. 5.8 ± 2.6 mm; p < 0.001). Conclusions: Intracranial aneurysms which rupture below 5 mm are not uncommon, and the factors associated with small-sized RIAs differ according to location. Sidewall aneurysms, with multiple aneurysms and Acom aneurysms with bilateral A1 may rupture even at small size.

Is there an inherited anatomical conformation favoring aneurysmal formation of the anterior communicating artery?

OBJECTIVE The pathophysiological mechanisms responsible for the formation of intracranial aneurysms (IAs) remain only partially elucidated. However, current evidence suggests a genetic component. The purpose of this study was to investigate the specific anatomical variations in the arterial complex that are associated with the presence of anterior communicating artery (ACoA) aneurysms in the familial forms of IAs. METHODS This multicenter study investigated bifurcation IAs in patients who had a sporadic ACoA IA without a family history of IA (SACAA group), in patients who had an ACoA IA with a family history of IA (FACAA group), and in their healthy first-degree relatives (HFDRs). Through the use of MR angiography (MRA) reconstructions, the symmetry of the A₁ segments and the angle between the A₁ and A₂ segments were analyzed on 3D models for each group. These measurements were then compared among the 3 groups. RESULTS Twenty-four patients with SACAA, 24 patients with FACAA, and 20 HFDRs were included in the study. Asymmetrical configuration of the A₁ segments was more frequent in the FACAA group than in the HFDR group (p = 0.002). The aneurysm-side A₁-A₂ angle was lower in the FACAA group (p = 0.003) and SACAA group (p = 0.007) than in the HFDR group. On the contralateral side, there was no difference in A₁-A₂ angles between groups. CONCLUSIONS The anatomical shape of the ACoA complex seems to be similarly associated with the presence of ACoA IAs in both the FACAA and SACAA groups. This highlights the role played by hemodynamic constraints in aneurysm formation and questions the hypothesis of the hereditary character of these anatomical shapes.

Morphological, Hemodynamic, and Clinical Independent Risk Factors for Anterior Communicating Artery Aneurysms

Background and Purpose—

The pathogenesis of cerebral aneurysms still raises some controversies. The aim of this study was to identify morphological, hemodynamic, and clinical independent risk factors for anterior communicating artery (ACoA) aneurysm development.

Methods—

Computed tomography angiography and transcranial color-coded sonography were performed in 77 patients with a nonbleeding ACoA aneurysm and in 73 controls. Symmetry of A1 segments of the anterior cerebral arteries, angles between A1 and A2 segments, tortuosity, diameter, mean velocity ( V m ), pulsatility index, and volume flow rate in both A1 segments were determined. Moreover, all study participants completed a survey on their medical history. Multivariate backward stepwise logistic regression analysis was performed to identify independent risk factors for ACoA aneurysm development.

Results—

Smoking, hypertension, asymmetry of A1 segments, the angle between A1 and A2 segments, A1 segment diameter, V m , pulsatility index, and volume flow rate turned out to be associated with the occurrence of ACoA aneurysms on univariate analysis. Multivariate analysis identified smoking (odds ratio, 2.036; 95% confidence interval, 1.277–3.245), asymmetry of A1 segments >40% (odds ratio, 2.524; 95% confidence interval, 1.275–4.996), pulsatility index (odds ratio, 0.004; 95% confidence interval, 0.000–0.124), and the angle between A1 and A2 segments ≤100° (odds ratio, 4.665; 95% confidence interval, 2.247–9.687) as independent strong risk factors for ACoA aneurysm development.

Conclusions—

The risk of ACoA aneurysm formation is determined by several independent clinical, morphological, and hemodynamic factors. The strongest independent risk factors include smoking, asymmetry of A1 segments >40%, low blood flow pulsatility, and the angle between A1 and A2 segments ≤100°.

The A1-A2 diameter ratio may influence formation and rupture potential of anterior communicating artery aneurysms

BACKGROUND

Specific morphological factors contribute to the hemodynamics of the anterior communicating artery (AComA). No study has examined the role of the A2 segment on AComA aneurysm presence and rupture.

OBJECTIVE

To examine the possibility that the ratio between A1 and A2 segments (A1-2 ratio) represents an independent risk factor for presence and rupture of AComA aneurysms (AComAAs).

METHODS

A retrospective review of an institutional aneurysm database was performed; patients with ruptured and unruptured AComAAs were identified. Two control groups were selected: group A (posterior circulation aneurysms) and group B (patients without intracranial aneurysms or other vascular malformations). Measurements of A1 and A2 diameters were obtained from digital subtraction angiography (64.1% of 3-D rotational digital subtraction angiography), and the A1-2 ratio calculated.

RESULTS

From January 2009 to April 2011, 156 patients were identified (52 AComAAs, 54 control group A, and 50 control group B). Mean age at the time of presentation was 56.09 years. Compared with both control groups, patients with AComAAs had greater A1 diameter (P < .01) and A1-2 ratio (P < .001) and smaller A2 diameter (P < .01). The A1-2 ratio correlated positively with the presence of AComAAs (P < .001). Ruptured AComAAs were smaller than unruptured ones (5.91 mm vs 9.25 mm, P = .02) and associated with a higher A1-2 Ratio (P = .02). The presence of a dominant A1 did not predict AComAA rupture (P = .15). The A1-2 ratio correlated positively with the presence of ruptured AComAAs (P = .04).

CONCLUSION

A1-2 ratio correlates positively with the presence and rupture of AComAAs and may facilitate treatment decision in cases of small, unruptured AComAAs.

Different long-term outcomes of abdominal aortic aneurysm and intracranial aneurysm models: hemodynamic change may also play an essential role in the initiation and progression of abdominal aortic aneurysm in rabbits

Self-healing phenomenon was found in the periarterial elastase-induced abdominal aortic aneurysm (AAA) in rabbit. This kind of aneurysm model does not progress and heals spontaneously in the long term, which is quite different from the performance of AAA disease in human. In order to better mimic human AAA and overcome this shortcoming of traditional AAA model in rabbit, we studied the pathogenesis of cerebral aneurysm (CA) model in small animal, which shows an excellent long-term patency and progressive enlargement. We found that hemodynamic conditions, such as turbulence flow, high blood flow, and shear stress, play an important role in the formation and progression of CA. So, we hypothesize that hemodynamic change may also play an essential role in the initiation and progression of rabbit AAA, and self-healing will be overcome if hemodynamic condition changes by coarctation of infra-renal aorta after elastase incubation.

Understanding the role of hemodynamics in the initiation, progression, rupture, and treatment outcome of cerebral aneurysm from medical image-based computational studies

About a decade ago, the first image-based computational hemodynamic studies of cerebral aneurysms were presented. Their potential for clinical applications was the result of a right combination of medical image processing, vascular reconstruction, and grid generation techniques used to reconstruct personalized domains for computational fluid and solid dynamics solvers and data analysis and visualization techniques. A considerable number of studies have captivated the attention of clinicians, neurosurgeons, and neuroradiologists, who realized the ability of those tools to help in understanding the role played by hemodynamics in the natural history and management of intracranial aneurysms. This paper intends to summarize the most relevant results in the field reported during the last years.