A combination of genetic, molecular and haemodynamic risk factors contributes to the formation, enlargement and rupture of brain aneurysms

Exploring the Landscape of Intracranial Aneurysms in South America: A Comprehensive Narrative Review Intracranial Aneurysms in South America

Exploring the landscape of intracranial aneurysms in South America unravels a complex interplay of epidemiological factors, clinical manifestations, and therapeutic challenges. The study methodically conducts a comprehensive literature review spanning the years 2003 to 2023, focusing on English-language articles obtained from diverse databases to elucidate the multifaceted nature of intracranial aneurysms in the region. Results and discussions categorize outcomes into positive domains, emphasizing successful treatments, favorable recoveries, and high survival rates, while also shedding light on negative aspects such as residual aneurysms and complications. The research illuminates significant gaps in pathological typing of intracranial aneurysms and exposes challenges in healthcare accessibility, notably the disparities in neurosurgical resources. Management challenges, including constrained infrastructure access, a neurosurgeon shortage, and gender disparities, are underscored. Transitioning to future prospects, the study advocates for strategic interventions, proposing expanded neurosurgical training, multidisciplinary approaches, improved funding, enhanced access to care, and fostering international collaborations. The study concludes by emphasizing the pivotal role of collaborative efforts, intensified training programs, and global partnerships in propelling intracranial aneurysm management forward in South America, ultimately contributing to enhanced patient outcomes across the region.

Greater hemodynamic stresses initiate aneurysms on major cerebral arterial bifurcations

Objective

To retrospectively investigate the hemodynamic stresses in initiating aneurysm formation on major cerebral arterial bifurcations with computational fluid dynamics (CFD) analysis.

Methods

The cerebral 3D angiographic data of major cerebral arterial bifurcations of the internal carotid, middle cerebral, anterior cerebral, and basilar arteries in 80 patients harboring bifurcation aneurysms and 80 control subjects with no aneurysms were retrospectively collected for the CFD analysis of hemodynamic stresses associated with aneurysm formation.

Results

Bifurcation angles at major bifurcations in all patients were significantly positively (P < 0.001) correlated with the age. At the center of direct flow impingement (CDFI) on the bifurcation wall, total pressure was the highest but dropped rapidly toward the branches. Wall shear stress, dynamic pressure, strain rate, and vorticity were lowest at the CDFI but they increased quickly toward the branches. The bifurcation angle was significantly (P < 0.001) enlarged in patients with bifurcation aneurysms than those without them, for all major arterial bifurcations. Most aneurysms leaned toward the smaller arterial branch or the arterial branch that formed a smaller angle with the parent artery, where the hemodynamic stresses increased significantly (P < 0.05), compared with those on the contralateral arterial branch forming a larger angle with the parent artery. Following the aneurysm development, all the hemodynamic stresses on the aneurysm dome decreased significantly (P < 0.001) compared with those at the initiation site on the bifurcation wall after virtual aneurysm removal. With the decrease of bifurcation angles, all the hemodynamic stresses decreased.

Conclusion

The formation of intracranial aneurysms on major intracranial arterial bifurcations is significantly associated with locally abnormally augmented hemodynamic stresses, which must be reduced.

Circular RNAs in vascular diseases

Vascular diseases are the leading cause of morbidity and mortality worldwide and are urgently in need of diagnostic biomarkers and therapeutic strategies. Circular RNAs (circRNAs) represent a unique class of RNAs characterized by a circular loop configuration and have recently been identified to possess a wide variety of biological functions. CircRNAs exhibit exceptional stability, tissue specificity, and are detectable in body fluids, thus holding promise as potential biomarkers. Their encoding function and stable gene expression also position circRNAs as an excellent alternative to gene therapy. Here, we briefly review the biogenesis, degradation, and functions of circRNAs. We summarize circRNAs discovered in major vascular diseases such as atherosclerosis and aneurysms, with a particular focus on molecular mechanisms of circRNAs identified in vascular endothelial cells and smooth muscle cells, in the hope to reveal new directions for mechanism, prognosis and therapeutic targets of vascular diseases.

The current landscape of intracranial aneurysms in Africa: management outcomes, challenges, and strategies-a narrative review

Intracranial aneurysms (IAs) pose complex and potentially life-threatening challenges in Africa, where limited resources, restricted access to specialised healthcare facilities, and disparities in healthcare provision amplify the difficulties of management. Timely diagnosis and treatment are pivotal in preventing complications, including subarachnoid haemorrhage. Treatment options encompass observation, surgical clipping, endovascular coiling, and flow diversion. Positive outcomes observed in IA management in Africa include high survival rates, favourable functional outcomes, successful treatment techniques, and the absence of complications in some cases. However, negative outcomes such as postoperative complications, reduced quality of life, perioperative mortality, and the risk of recurrence persist. Challenges in IA management encompass limited access to diagnostic tools, a scarcity of specialised healthcare professionals, and an unequal distribution of services. Addressing these challenges requires interventions focused on improving access to diagnostic tools, expanding the number of trained professionals, and establishing specialised IA treatment centres. Collaboration, research, and capacity-building efforts hold significant importance in improving patient outcomes and reducing disparities in IA management across Africa.

Integrated analysis identifies the IL6/JAK/STAT signaling pathway and the estrogen response pathway associated with the pathogenesis of intracranial aneurysms

Objective

We intended to identify the potential key biomarker and pathways that correlated with infiltrating immune cells during the pathogenesis of intracranial aneurysms (IA), to develop a diagnostic model, and to predict therapeutic drugs.

Methods

Three datasets containing intracranial aneurysm tissue samples and normal artery control samples from Gene Expression Omnibus (GEO) were included. Gene-set variation analysis(GSVA) and gene set enrichment analysis (GSEA) were conducted to find the significant differentially expressed pathways in IA formation. The least absolute shrinkage and selection operator (LASSO) regression and the multivariate logistic regression analysis were performed to identify the characteristic genes in the IL6/JAK/STAT signaling pathway (ISP) and the estrogen response pathway (ERP). A diagnostic model was constructed. xCell was used to identify immune cell types in IA pathogenesis. We used the weighted gene co-expression network analysis (WGCNA) algorithm to explore the correlations between the key modules and the four traits. Potential therapeutic drugs were investigated in Enrichr and Drugbank database.

Results

The ISP is significant positively correlated with IA onset. The biological function of the ISP is positively correlated with that of the ERP, and is significantly associated with immune cells activities. CSF2RB, FAS, IL6, PTPN1, STAT2, TGFB1 of the ISP gene set and ALDH3A2, COX6C, IGSF1, KRT18, MICB, NPY1R of the ERP gene set were proved to be the characteristic genes. The STAT2 gene can be the potential biomarker of IA onset. The immune score of IA samples was significantly higher than the controls. The STAT2 gene expression is associated with infiltration of immune cells. The WGCNA results were consistent with our finds. Acetaminophen can be a potential therapeutic drug for IA targeting STAT2.

Conclusions

We identified that the ISP was one of the most significant positively correlated pathways in IA onset, and it was activated in this process concordant with the ERP and immune responses. Except for beneficial effects, complex and multiple roles of estrogen may be involved in IA formation. STAT2 could be a potential biomarker and a promising therapeutic target of IA pathogenesis.

Computational fluid dynamic analysis of the initiation of cerebral aneurysms

OBJECTIVE

Relationships between aneurysm initiation and hemodynamic factors remain unclear since de novo aneurysms are rarely observed. Most previous computational fluid dynamics (CFD) studies have used artificially reproduced vessel geometries before aneurysm initiation for analysis. In this study, the authors investigated the hemodynamic factors related to aneurysm initiation by using angiographic images in patients with cerebral aneurysms taken before and after an aneurysm formation.

METHODS

The authors identified 10 cases of de novo aneurysms in patients who underwent follow-up examinations for existing cerebral aneurysms located at a different vessel. The authors then reconstructed the vessel geometry from the images that were taken before aneurysm initiation. In addition, 34 arterial locations without aneurysms were selected as control cases. Hemodynamic parameters acting on the arterial walls were calculated by CFD analysis.

RESULTS

In all de novo cases, the aneurysmal initiation area corresponded to the highest wall shear stress divergence (WSSD point), which indicated that there was a strong tensile force on the arterial wall at the initiation area. The other previously reported parameters did not show such correlations. Additionally, the pressure loss coefficient (PLc) was statistically significantly higher in the de novo cases (p < 0.01). The blood flow impact on the bifurcation apex, or the secondary flow accompanied by vortices, resulted in high tensile forces and high total pressure loss acting on the vessel wall.

CONCLUSIONS

Aneurysm initiation may be more likely in an area where both tensile forces acting on the vessel wall and total pressure loss are large.

Fluid-structure interaction (FSI) simulation for studying the impact of atherosclerosis on hemodynamics, arterial tissue remodeling, and initiation risk of intracranial aneurysms

The biomechanical and hemodynamic effects of atherosclerosis on the initiation of intracranial aneurysms (IA) are not yet clearly discovered. Also, studies for the observation of hemodynamic variation due to atherosclerotic stenosis and its impact on arterial remodeling and aneurysm genesis remain a controversial field of vascular engineering. The majority of studies performed are relevant to computational fluid dynamic (CFD) simulations. CFD studies are limited in consideration of blood and arterial tissue interactions. In this work, the interaction of the blood and vessel tissue because of atherosclerotic occlusions is studied by developing a fluid and structure interaction (FSI) analysis for the first time. The FSI presents a semi-realistic simulation environment to observe how the blood and vessels' structural interactions can increase the accuracy of the biomechanical study results. In the first step, many different intracranial vessels are modeled for an investigation of the biomechanical and hemodynamic effects of atherosclerosis in arterial tissue remodeling. Three physiological conditions of an intact artery, the artery with intracranial atherosclerosis (ICAS), and an atherosclerotic aneurysm (ACA) are employed in the models with required assumptions. Finally, the obtained outputs are studied with comparative and statistical analyses according to the intact model in a normal physiological condition. The results show that existing occlusions in the cross-sectional area of the arteries play a determinative role in changing the hemodynamic behavior of the arterial segments. The undesirable variations in blood velocity and pressure throughout the vessels increase the risk of arterial tissue remodeling and aneurysm formation.

The Cerebral Arterial Wall in the Development and Growth of Intracranial Aneurysms

A considerable number of people harbor intracranial aneurysms (IA), which is a focal or segmental disease of the arterial wall. The pathophysiologic mechanisms of IAs formation, growth, and rupture are complex. The mechanism also differs with respect to the type of aneurysm. In broad aspects, aneurysms may be considered a disease of the vessel wall. In addition to the classic risk factors and the genetic/environmental conditions, altered structural and pathologic events along with the interaction of the surrounding environment and luminal flow dynamics contribute to the aneurysm’s development and growth. In this review, we have tried to simplify the complex interaction of a multitude of events in relation to vessel wall in the formation and growth of IAs.

Morphological and Hemodynamic Characteristics Associated With the Rupture of Multiple Intracranial Aneurysms

Background and Purpose

The objective of this study was to identify the morphological and hemodynamic factors associated with the rupture of multiple intracranial aneurysms regardless of patient-related factors and establish a statistical model for aneurysm rupture risk assessment.

Methods

The digital subtraction angiography (DSA) data of 104 mirror intracranial aneurysms in 52 consecutive patients were retrospectively analyzed in this study. 21 morphological parameters and hemodynamic parameters were calculated by 3-dimensional reconstruction and computational fluid dynamics (CFD) simulation. Significant differences (p < 0.05) between the two groups were subsequently tested with the multivariate logistic regression to identify the independent risk factors. A prediction model was established based on the independent risk factors. The receiver operating characteristics (ROCs) were generated to estimate the prediction performance. A cohort of patients with multiple intracranial aneurysms admitted in our institute from January 2021 to October 2021 was introduced to verify the value of the model.

Results

Significant differences between the ruptured and unruptured aneurysms were found in 15 out of 19 parameters. Bleb formation, neck width, and size ratio were independent factors in the multivariate logistic regression. A prediction model based on the three independent risk factors was established: Odds = −1.495 – 0.707 × _(Neckwidth) + 3.061 × _{(Blebformation)} + 2.1 × _(SR) (bleb formation: Yes = 1, No = 0). The area under the curve (AUC) value of the model was 0.901. In the validation cohort, the prediction model showed satisfying performance in assessing multiple aneurysm rupture risk with a sensitivity of 100% and specificity of 88.46%.

Conclusion

Bleb formation, neck width, and size ratio were independently associated with aneurysm rupture status. The prediction model may help in identifying the aneurysm with high rupture risk.

Greater hemodynamic stresses initiated the anterior communicating artery aneurysm on the vascular bifurcation apex

OBJECTIVE

To investigate hemodynamic stresses associated with the anterior communicating artery (Acom) aneurysm formation using computational fluid dynamics (CFD) analysis.

METHODS

Three-dimensional geometries of the anterior cerebral artery (ACA) bifurcations in 20 patients with Acom aneurysms and 20 control subjects were used for CFD analysis to investigate hemodynamic stresses including the total and dynamic pressure, wall shear stress (WSS), vorticity and strain rate.

RESULTS

At the direct flow impinging center on the bifurcation apex, the total pressure was the maximal but decreased quickly from the impinging center to both daughter branches. The WSS, dynamic pressure, vorticity and strain rate were the minimal at the direct impinging center but increased rapidly and reached the peaks at both daughter branches. The ACA bifurcation angle was significantly (P < 0.001) greater in patients with than without Acom aneurysms (144.2° ± 4.1° vs. 105.1° ± 3.2°). Most aneurysms (70% and 85%, respectively) were deviated to the smaller daughter branch or to the daughter branch forming a smaller angle with the A1 segment of ACA, where the hemodynamic stresses were significantly (P < 0.05) greater than those on the contralateral daughter branch. After aneurysm formation, the hemodynamic stresses on the aneurysm dome were all significantly decreased compared with at the aneurysm initiation site with aneurysm virtual removal (P < 0.001).

CONCLUSION

Formation of the Acom aneurysm is closely associated with and is to decrease the locally abnormally enhanced hemodynamic stresses.

Multiple and mirror intracranial aneurysms: study of prevalence and associated risk factors

OBJECTIVE

Multiple intracranial aneurysms (MIA) account for 30% of all intracranial aneurysms, while mirror aneurysms, a subgroup of MIA, are present in 5% of all patients with cerebral aneurysms. We investigated the risk factors associated with the presence of multiple and mirror intracranial aneurysms.

METHODS

1404 patients, 314 males (22.4%) and 1090 female (77.6%) were enrolled for this study. Diagnosis was performed with a digital subtraction angiography (DSA). Multiplicity was defined as the presence of two or more aneurysms and mirror aneurysms as one pair of aneurysms involving bilateral corresponding arteries. Patients were followed-up from September 2009 till August 2018. Individuals' characteristics such as sex, age, smoking, hypertension and use of contraceptives were evaluated.

RESULTS

Five hundred and twelve patients (36.4%) were diagnosed with MIA, approximately 4%/year. We observed 203 pairs of mirror aneurysms, accounting for 406 aneurysms (13% of the population). There was an increased frequency of females with multiple (p < 0.001, OR = 1.883, 95% CI = 1.386-2.560) and mirror aneurysms (p < 0.001, OR = 2.828, 95% CI = 1.725-4.636). Smoking was associated with multiplicity (p< 0.001, OR = 1.458, 95% CI = 1.160-1.833), as well as advanced age (p < 0.001, OR = 1.938, 95% CI = 1.438-2.611), but there was no significant relation with presence of mirror aneurysms. We observed higher frequency of baby aneurysms (<3mm) in the group of patients with MIA, while giant aneurysms (>25 mm) were most found in patients with only one aneurysm (p < 0.001). No differences between patients who used contraceptives against patients who did not use were found (p = 0.600).

CONCLUSIONS

Gender and smoking, known risk factors to the development of a single intracranial aneurysm, are proportionally increased in patients with MIA. Hypertension and oral contraceptives were not associated with multiplicity.

Ratio of IL-8 in CSF versus Serum Is Elevated in Patients with Unruptured Brain Aneurysm

Only scarce data pertaining to interleukin 8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) chemokines in human aneurysm can be found in the current literature. Therefore, the aim of this study was the evaluation of cerebrospinal fluid (CSF) and serum IL-8 and MCP-1 concentration in unruptured intracranial aneurysm (UIA) patients (n = 25) compared to the control group (n = 20). IL-8 and MCP-1 concentrations were measured with ELISA method. We demonstrated that CSF IL-8 concentration of UIA patients is significantly higher (p < 0.001) than that presented in the serum, which can indicate its local synthesis within central nervous system. CSF IL-8 concentration was also significantly related to aneurysm size, which may reflect the participation of IL-8 in the formation and development of brain aneurysms. IL-8 Quotient (CSF IL-8 divided by serum IL-8) in UIA patients was statistically higher compared to control individuals (p = 0.045). However, the diagnostic utility analysis did not equivocally indicate the diagnostic usefulness of the IL-8 Quotient evaluation in brain aneurysm patients. Nevertheless, this aspect requires further study.

Automated and objective removal of bifurcation aneurysms: Incremental improvements, and validation against healthy controls

Abnormal hemodynamic stresses are thought to correlate with aneurysm initiation, growth, and rupture. We have previously investigated the role of wall shear stress (WSS) and WSS gradients (WSSG) in search for a mechanistic link to formation of sidewall aneurysms using an automated and objective tool for aneurysm removal and arterial reconstruction in combination with computational fluid dynamics (CFD). However, we warned against the use of the tool for bifurcation type aneurysms because of a potential unrealistic reconstruction of the apex. We hypothesized that inclusion of additional morphological features from the surrounding vasculature could overcome these constraints. We extended the previously published method for removal and reconstruction of the bifurcation vasculature based on diverging and converging points of the parent and daughter artery centerlines, to also include two new centerlines between the daughter vessels, one of them passed through the bifurcation center. Validation was performed by comparing the efficacy of the two algorithms, using ten healthy models of the internal carotid artery terminus as ground truth. Qualitative results showed that the bifurcation apexes became smoother relative to the original algorithm; more consistent with the reference models. This was reflected quantitatively by a reduced maximum distance between the reference and reconstructed surfaces, although not statistically significant. Furthermore, the modified algorithm also quantitatively improved CFD derived WSS and WSSG, especially the latter. In conclusion, the modified algorithm does not perfectly reconstruct the bifurcation apex, but provides an incremental improvement, especially important for the derived hemodynamic metrics of interest in vascular pathobiology.

Hemodynamic Characteristics Associated With Paraclinoid Aneurysm Recurrence in Patients After Embolization

Objective: To investigate the hemodynamic features before and after embolization of paraclinoidal aneurysms using hemodynamic numerical simulation and the influence of embolization on recurrence after embolization.

Methods: From January 2016 to December 2017, we enrolled a total of 113 paraclinoidal aneurysms treated with embolization. They were divided into recurrent group and stable group depending on follow-up results. An aneurysm model was generated based on 3D-DSA before and after embolization. The hemodynamic characteristics were analyzed between two groups using Computational fluid dynamic (CFD).

Results: In the recurrent group, the peak systolic WSS, OSI and velocity around the aneurysm neck areas prior to embolization were 20.47 ± 3.04 Pa, 0.06 ± 0.02 and 0.07 ± 0.03 m/s, respectively. These values were 23.50 ± 4.11 Pa, 0.06 ± 0.01 and 0.11 ± 0.02 m/s, respectively in the stable group (P > 0.05). The WSS, OSI, velocity around the same areas in the recurrent group after embolization were 35.59 ± 8.75 Pa, 0.07 ± 0.02 and 0.12 ± 0.03 m/s, respectively (P < 0.01). In the stable group, the WSS, OSI and velocity were 13.08 ± 2.89 Pa, 0.04 ± 0.01 and 0.07 ± 0.02 m/s, respectively (P < 0.01). After embolization, the WSS, OSI and velocity around the aneurysm neck areas in the recurrent group were significantly higher than those in the stable group.

Conclusions: High peak systolic WSS, OSI and velocity around aneurysm neck areas after embolization of paraclinoidal aneurysms may be important factors leading to recurrence.

Relationship between hemodynamic parameters and cerebral aneurysm initiation

Research on the relationship between cerebralaneurysm initiation and hemodynamic parameters, but several open questions remain on initiation and growth mechanisms of cerebral aneurysms. If factors contributing to initiation were identified, it would be possible to predict the initiation of aneurysms. The purpose of this study is to investigate the relationship between cerebral aneurysm initiation and hemodynamic factors. Blood flow simulations in aneurysms of three patients were performed using computational fluid dynamics (CFD) based on the cerebral blood vessel geometry before aneurysm initiation. We evaluated pressure, wall shear stress (WSS), wall shear stress gradient (WSSG), oscillatory shear index (OSI) and gradient oscillatory number (GON) since these factors are known to be associated with aneurysmal initiation. We also focused on the wall shear stress divergence (WSSD) in particular on the direction of WSS. Our results indicated that only high WSSD regions corresponded to the initiation regions, and the value of WSSD was remarkably high. Stretching force to the vessel wall may be related to the initiation of cerebral aneurysms.

The hypertension of hemophilia is associated with vascular remodeling in the joint

OBJECTIVE

Hemophilic arthropathy is associated with pronounced vascular joint remodeling. Also, compared to the general population, PWH have a higher prevalence of hypertension not explained by usual risk factors. As vascular remodeling in various vascular beds is a hallmark of hypertension, we hypothesized that vascular joint remodeling is associated with elevated blood pressures and hypertension.

METHODS

Elbows, knees, and ankles of 28 adult PWH were evaluated for vascular abnormalities with MSKUS/PD, as well as for radiographic and clinical status and pain. Logistic and linear regression models were fitted to examine associations between hypertension, blood pressure, and PD score.

RESULTS

The extent of vascular abnormalities was associated with hypertension and blood pressures. Hypertensive patients had a higher PD score compared to nonhypertensive patients, and the risk of hypertension increased steeply with PD score. SBP was also strongly associated with PD score, while DBP was only weakly associated.

CONCLUSIONS

Vascular remodeling in hemophilic joints is associated with hypertension and elevated blood pressures. As hypertension is a grave risk factor for intracranial hemorrhage, a prominent cause of mortality in hemophilia patients, future studies are needed to address the causal pathways between vascular joint remodeling and blood pressure.

Aberrant Expression of microRNA-9 Contributes to Development of Intracranial Aneurysm by Suppressing Proliferation and Reducing Contractility of Smooth Muscle Cells

BACKGROUND MiR-9 is reportedly involved with many diseases, such as acute myeloid leukemia and liver oncogenesis. In the present study we investigated the molecular mechanism, including the potential regulator and signaling pathways, of MYOCD, which is the gene that in humans encodes the protein myocardin. MATERIAL AND METHODS We searched the online miRNA database (www.mirdb.org) with the "seed sequence" located within the 3'-UTR of the target gene, and then validated MYOCD to be the direct gene via luciferase reporter assay system, and further confirmed it in cultured cells by using Western blot analysis and realtime PCR. RESULTS We established the negative regulatory relationship between miR-9 and MYOCD via studying the relative luciferase activity. We also conducted realtime PCR and Western blot analysis to study the mRNA and protein expression level of MYOCD between different groups (intracranial aneurysm vs. normal control) or cells treated with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors, indicating the negative regulatory relationship between miR-9 and MYOCD. We also investigated the relative viability of smooth muscle cells when transfected with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors to validate that miR-9 t negatively interferes with the viability of smooth muscle cells. We then investigated the relative contractility of smooth muscle cells when transfected with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors, and the results showed that miR-9 weakened contractility. CONCLUSIONS Our findings show that dysregulation of miR-9 is responsible for the development of IA via targeting MYOCD. miR-9 and its direct target, MYOCD, might novel therapeutic targets in the treatment of IA.

Patient and aneurysm characteristics associated with rupture risk of multiple intracranial aneurysms in the anterior circulation system

BACKGROUND

Multiple intracranial aneurysms (MIAs) are associated with poorer outcomes after rupture than are single intracranial aneurysms (SIAs). Although the risk factors for intracranial aneurysm rupture have been widely investigated, few studies have focused on MIAs. Thus, the present study aimed to determine whether there are differences in the patient and aneurysm characteristics between those with ruptured and unruptured anterior circulation MIAs (AC-MIAs).

METHOD

The present study included 97 patients with AC-MIAs (58 ruptured, 39 unruptured). Data regarding patient characteristics, aneurysm location, mirror aneurysms (MirAns), and bleb formations were collected from medical records and angiography images. Three-dimensional (3D) geometries generated with a 3D Slicer were evaluated to determine the range of morphological parameters. A univariate analysis was conducted to identify significant differences between the groups and receiver-operating characteristic (ROC) analyses were performed for each morphological parameter.

RESULTS

There are significantly fewer patients younger than 40 years of age in the ruptured group (P = 0.04); although the groups did not significantly differ with regard to smoking and hypertension, the ruptured group included significantly more current smokers who smoked more than 20 cigarettes per day (P = 0.025) and significantly more patients with a history of hypertension but an irregular use of anti-hypertensive medications (P = 0.043). Ruptured AC-MIAs were more likely to be located in the internal carotid artery (ICA) communicating artery (ICA C7) and anterior communicating artery (AComA; P = 0.000), to have formed a pair of MirAns (P = 0.001), and to have a bleb formation (P = 0.000). In terms of morphological parameters, the two groups differed significantly regarding aneurysm size (P = 0.000), neck width (P = 0.016), bottleneck factor (BNF; P = 0.000), height/width ratio (H/W; P = 0.031), aspect ratio (AR; P = 0.000) and size ratio (SR; P = 0.000). Additionally, the ROC analyses revealed that the optimal threshold size for rupture was 4.00 mm and that the SR had the highest area under the curve (AUC) value (0.826).

CONCLUSIONS

The present study found that current smokers who smoked more than 20 cigarettes per day and those with hypertension but an irregular use of anti-hypertensive medications were more likely to suffer from rupture. Aneurysm location and bleb formation were closely related to the rupture of AC-MIAs, and SR was a better predictor of AC-MIAs rupture status than size, neck width, BNF, H/W and AR. These findings should be verified by future prospective follow-up studies of AC-MIAs.

Low prevalence of fetal-type posterior cerebral artery in patients with basilar tip aneurysms

Background

Basilar tip aneurysms (BTA) are multifactorial in origin, with luminal forces playing a major role in their formation. Considering the reduced hemodynamic stress on the basilar apex in the fetal-type posterior cerebral artery (fPCA), we hypothesize that BTA should be less common in patients with this variant.

Objective

To investigate, in a retrospective case–control study, the frequency of fPCA in patients with and without BTA.

Materials and methods

We collected clinical and imaging data from consecutive patients with BTA undergoing catheter angiography between July 2010 and July 2015, and from a randomly selected, age- and sex-matched non-BTA control population from our prospective database. Anatomical variants of the distal basilar artery region were assessed in the two groups and compared using parametric and non-parametric tests.

Results

Fifty-nine BTA cases and 337 controls were included. fPCA was present in 3% of patients with BTA and 23% in the control group (p<0.001; OR=0.11, 95% CI 0.03 to 0.48). Basilar tip disposition was cranial in 49% of BTA and 63% of non-BTA cases (p=0.04; OR=0.57, 95% CI 0.33 to 0.99); a caudal disposition was found in 24% and 6% of cases, respectively (p<0.001; OR=4.65, 95% CI 2.21 to 9.80).

Conclusions

We found a statistically significant association between the absence of fPCA and BTA. Our findings underline the importance of hemodynamic stress in the formation of intracranial aneurysms, and suggest that fPCA is a protective variant for formation of BTA.

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.

Hemodynamic alterations after stent implantation in 15 cases of intracranial aneurysm

BACKGROUND

Stent-assisted coiling technology has been widely used in the treatment of intracranial aneurysms. In the current study, we investigated the intra-aneurysmal hemodynamic alterations after stent implantation and their association with the aneurysm location.

METHODS

We first retrospectively studied 15 aneurysm cases [8 internal carotid artery-ophthalmic artery (ICA-OphA) aneurysms and 7 posterior communicating artery (PcoA) aneurysms] treated with Enterprise stents and coils. Then, based on the patient-specific geometries before and after stenting, we built virtual stenting computational fluid dynamics (CFD) simulation models.

RESULTS

Before and after the stent deployment, the average wall shear stress (WSS) on the aneurysmal sac at systolic peak changed from 7.04 Pa (4.14 Pa, 15.77 Pa) to 6.04 Pa (3.86 Pa, 11.13 Pa), P = 0.001; the spatially averaged flow velocity in the perpendicular plane of the aneurysm dropped from 0.5 m/s (0.28 m/s, 0.7 m/s) to 0.33 m/s (0.25 m/s, 0.49 m/s), P = 0.001, respectively. Post stent implantation, the WSS in ICA-OphA aneurysms and PcoA aneurysms decreased by 14.4 % (P = 0.012) and 16.6 % (P = 0.018), respectively, and the flow velocity also reduced by 10.3 % (P = 0.029) and 10.5 % (P = 0.013), respectively. Changes in the WSS, flow velocity, and pressure were not significantly different between ICA-OphA and PcoA aneurysms (P > 0.05). Stent implantation did not significantly change the peak systolic pressure in either aneurysm type.

CONCLUSION

After the stent implantation, both the intra-aneurysmal flow velocity and WSS decreased independently of aneurysm type (ICA-OphA and PcoA). Little change was observed in peak systolic pressure.

Distribution of ABO blood groups in the patients with intracranial aneurysm and association of different risk factors with particular blood type

Introduction:

The association between ABO blood groups and intracranial aneurysms is not well-known. Many co-morbid factors are associated with intracranial aneurysms. Our objective was to assess the prevalence of different blood group in patients with intracranial aneurysm and to look for associations between risk factors and these groups.

Materials and Methods:

This retrospective study includes 1,491 cases who underwent surgical operations for intracranial aneurysms from 1993-2014. We have evaluated the information related to clinical history, ABO blood groups and associated risk factors in the patients both ruptured and unruptured intracranial aneurysms by chart review of the cases.

Results:

In our study, out of 1,491 cases, the most common ABO blood groups were group O (668 cases, 44.80%) and Group A (603 cases, 40.44%), and Rh(+) in 1,319 (88.4%) and Rh(-) in 147 (11.6%). Blood Group A (43% vs. 36%) and Group B (16.2% vs. 8.6%) were significantly higher in Caucasian and African Americans respectively. However, in general population, there was no significant difference in blood groups between Caucasians and African Americans. Rh(-) factor was significantly higher in Caucasians compared to African Americans. Incidence of smoking was significantly higher in aneurysm patients with O group compared to others. In addition, incidence of hypercholesterolemia was significantly higher in aneurysm patients with A group compared to others.

Conclusion:

The racial disparity in the distribution of blood groups, and risk factor association with blood groups in the development of intracranial aneurysm needs to be considered. The findings from our study may be useful in identifying patients at increased risk. Further study may be required to establish the risks from multiple centers studies around the world.

Wall Mechanical Properties and Hemodynamics of Unruptured Intracranial Aneurysms

BACKGROUND AND PURPOSE

Aneurysm progression and rupture is thought to be governed by progressive degradation and weakening of the wall in response to abnormal hemodynamics. Our goal was to investigate the relationship between the intra-aneurysmal hemodynamic conditions and wall mechanical properties in human aneurysms.

MATERIALS AND METHODS

A total of 8 unruptured aneurysms were analyzed. Computational fluid dynamics models were constructed from preoperative 3D rotational angiography images. The aneurysms were clipped, and the domes were resected and mechanically tested to failure with a uniaxial testing system under multiphoton microscopy. Linear regression analysis was performed to explore possible correlations between hemodynamic quantities and the failure characteristics and stiffness of the wall.

RESULTS

The ultimate strain was correlated negatively to aneurysm inflow rate (P = .021), mean velocity (P = .025), and mean wall shear stress (P = .039). It was also correlated negatively to inflow concentration, oscillatory shear index, and measures of the complexity and instability of the flow; however, these trends did not reach statistical significance. The wall stiffness at high strains was correlated positively to inflow rate (P = .014), mean velocity (P = .008), inflow concentration (P = .04), flow instability (P = .006), flow complexity (P = .019), wall shear stress (P = .002), and oscillatory shear index (P = .004).

CONCLUSIONS

In a study of 8 unruptured intracranial aneurysms, ultimate strain was correlated negatively with aneurysm inflow rate, mean velocity, and mean wall shear stress. Wall stiffness was correlated positively with aneurysm inflow rate, mean velocity, wall shear stress, flow complexity and stability, and oscillatory shear index. These trends and the impact of hemodynamics on wall structure and mechanical properties should be investigated further in larger studies.

RUPTURE MODEL OF INTRACRANIAL SACCULAR ANEURYSMS DUE TO HYPERTENSION

The risk of rupture of intracranial saccular aneurysms is one of the leading dilemmas for patients and neurologists. Although the probability of rupture is small, the consequences of rupture are usually fatal or crippling, and a concern for the patient is whether or not to treat an existing aneurysm. In this paper, an idealized model of saccular aneurysms with assumed Fung material behavior was investigated for rupture potential when the stresses exceeded the maximum wall strength of the aneurysm wall. Numerical simulations used various levels of blood pressure, from normal to hypertensive, in order to determine correlations of aneurysm size and risk of rupture. Results showed that hypertensive individuals harboring cerebral aneurysms with a size of at least 6 mm are at risk.

Genetic investigations on intracranial aneurysm: update and perspectives

Detection of an intracranial aneurysm (IA) is a common finding in MRI practice. Nowadays, the incidence of unruptured IA seems to be increasing with the continuous evolution of imaging techniques. Important modifiable risk factors for SAH are well defined, but familial history of IA is the best risk marker for the presence of IA. Numerous heritable conditions are associated with IA formation but these syndromes account for less than 1% of all IAs in the population. No diagnostic test based on genetic knowledge is currently available to identify theses mutations and patients who are at higher risk for developing IAs. In the longer term, a more comprehensive understanding of independent and interdependent molecular pathways germane to IA formation and rupture may guide the physician in developing targeted therapies and optimizing prognostic risk assessment.

Aneurysmal subarachnoid hemorrhage: relationship to solar activity in the United States, 1988-2010

Aneurysmal subarachnoid hemorrhage (SAH) is a common condition treated by neurosurgeons. The inherent variability in the incidence and presentation of ruptured cerebral aneurysms has been investigated in association with seasonality, circadian rhythm, lunar cycle, and climate factors. We aimed to identify an association between solar activity (solar flux and sunspots) and the incidence of aneurysmal SAH, all of which appear to behave in periodic fashions over long time periods. The Nationwide Inpatient Sample (NIS) provided longitudinal, retrospective data on patients hospitalized with SAH in the United States, from 1988 to 2010, who underwent aneurysmal clipping or coiling. Solar activity and SAH incidence data were modeled with the cosinor methodology and a 10-year periodic cycle length. The NIS database contained 32,281 matching hospitalizations from 1988 to 2010. The acrophase (time point in the cycle of highest amplitude) for solar flux and for sunspots were coincident. The acrophase for aneurysmal SAH incidence was out of phase with solar activity determined by non-overlapping 95% confidence intervals (CIs). Aneurysmal SAH incidence peaks appear to be delayed behind solar activity peaks by 64 months (95% CI; 56-73 months) when using a modeled 10-year periodic cycle. Solar activity (solar flux and sunspots) appears to be associated with the incidence of aneurysmal SAH. As solar activity reaches a relative maximum, the incidence of aneurysmal SAH reaches a relative minimum. These observations may help identify future trends in aneurysmal SAH on a population basis.

Estrogen signaling through estrogen receptor beta and G-protein-coupled estrogen receptor 1 in human cerebral vascular endothelial cells: implications for cerebral aneurysms

Little is known about estrogen receptors and their signaling mechanisms in human cerebral vascular endothelial cells, which is important for understanding cerebral aneurysm pathogenesis in menopausal and postmenopausal women. Estrogen receptor beta (ERβ) and G-protein-coupled receptor 1 (GPER1) were immunocytochemically identified in human cerebral vascular endothelial cells (HCVECs). ERβ was mainly located at the nuclei of the cells while GPER1 was located at the plasma membrane. Interaction events between 17β-estradiol and ERβ or GPER1 in HCVECs were evaluated by in situ proximity ligation assay. The number of interaction events between 17β-estradiol and ERβ was positively correlated with 17β-estradiol concentrations (r = 0.9614, P < 0.01). The interaction events between 17β-estradiol and GPER1 were dose responsive. Our data support HCVECs to serve as a suitable cellular model for studying cerebral aneurysm pathogenesis in menopausal and postmenopausal women. Subtypes of estrogen receptors and their signaling mechanisms identified in HCVECs could be applicable for developing estrogen-like compounds to specifically bind to a subtype of estrogen receptors with greater specific action on the cerebral arteries, without the estrogen-dependent side effects on the reproductive organs, to prevent cerebral aneurysm formation in menopausal and postmenopausal woman.