Article

Quantified aneurysm shape and rupture risk

March 2005
Journal of Neurosurgery 102(2):355-62

DOI:10.3171/jns.2005.102.2.0355

Source
PubMed

Authors:

Madhavan Raghavan

University of Iowa

Baoshun Ma

University of Vermont

The authors investigated whether quantified shape or size indices could better discriminate between ruptured and unruptured aneurysms. Several custom algorithms were created to quantifiy the size and shape indices of intracranial aneurysms by using three-dimensional computerized tomography angiography models of the brain vasculature. Data from 27 patients with ruptured or unruptured aneurysms were evaluated in a blinded fashion to determine whether aneurysm size or shape better discriminated between the ruptured and unruptured groups. Five size and eight shape indices were calculated for each aneurysm. Two-tailed independent Student t-tests (significance p < 0.05) were used to determine statistically significant differences between ruptured and unruptured aneurysm groups for all 13 indices. Receiver-operating characteristic-area under curve analyses were performed for all indices to quantify the predictability of each index and to identify optimal threshold values. None of the five size indices were significantly different between the ruptured and unruptured aneurysms. Five of the eight shape indices were significantly different between the two lesion groups, and two other shape indices showed a trend toward discriminating between ruptured and unruptured aneurysms, although these differences did not reach statistical significance. Quantified shape is more effective than size in discriminating between ruptured and unruptured aneurysms. Further investigation will determine whether quantified aneurysm shape will prove to be a reliable predictor of aneurysm rupture.

Multidimensional Comparison of Microsurgical Clipping and Endovascular Techniques for Anterior Communicating Artery Aneurysms: Balancing Occlusion Rates and Periprocedural Risks

Article

Full-text available

Mar 2025
MED LITH

Background and Objectives: The anterior communicating artery is a common location for intracranial aneurysms. Anterior communicating artery aneurysms (AcomA) pose a significant risk of rupture. Treatment options include microsurgical clipping and endovascular techniques, but the optimal approach remains controversial. This study aims to compare the outcomes of these two treatment modalities in a single-center patient cohort using a comprehensive matching process based on clinical and morphological parameters. Materials and Methods: A retrospective analysis was conducted on 1026 patients with 1496 intracranial aneurysms treated between 2000 and 2018. After excluding cases lacking 3D angiography or aneurysms in other locations or without treatment, 140 AcomA were selected. The study matched 24 surgically treated AcomA cases with 116 endovascularly treated cases based on 21 morphological and clinical criteria, including age, sex, Hunt and Hess score, and Fisher grade. Results: The microsurgical clipping group demonstrated a significantly higher rate of complete aneurysm occlusion compared to the endovascular group (p = 0.007). However, this was associated with a higher incidence of postoperative ischemic complications in the surgical group (13 out of 24 cases) compared to the endovascular group (2 out of 116 cases). Despite these complications, no significant differences were found in clinical outcomes at discharge or follow-up, as measured by the modified Rankin Scale (p > 0.999). Both groups had comparable rates of hydrocephalus, vasospasm, and delayed cerebral ischemia. Conclusions: Microsurgical clipping resulted in higher aneurysm occlusion rates but carried an increased risk of ischemic complications compared to endovascular treatment. Clinical outcomes were comparable between the two modalities, suggesting that treatment decisions should be individualized based on aneurysm characteristics and patient factors. Further prospective studies are warranted to optimize treatment strategies for AcomA.

Inter-modality correlation across invasive and noninvasive angiography in the three-dimensional assessment of cerebral aneurysms

Article

Full-text available

Feb 2025

Background Non-invasive and invasive methods of cerebral angiography, including computed tomography angiography (CTA), magnetic resonance angiography (MRA), and digital subtraction angiography (DSA), are commonly used to characterize and follow cerebral aneurysms. Prior work has validated two-dimensional size measurements across these modalities. Our study aims to compare the reliability of three-dimensional (3D) shape measurements across CTA, MRA, and DSA. Methods A subset of cerebral aneurysms in which more than one form of angiography was performed was selected. Aneurysms were included if they did not change in size or shape between angiographic studies. Aneurysm domes were segmented, and morphometric features were measured consistent with prior reports. Intraclass correlation coefficients (ICCs) for each morphometric measure were calculated using a two-way mixed effect model. Results A total of 65 individual aneurysms from 55 patients were included in the study. The majority of aneurysms were imaged with DSA and CTA (43%) or MRA and CTA (40%), with 14% having DSA, MRA, and CTA available for review. The majority of aneurysms were located in the anterior circulation (77%), with an average size was 5 (4–8) mm. ICC ranged from 0.66 to 0.99 for 3D morphometric features, corresponding to “moderate” to “excellent” correlation. Sphericity and non-sphericity index showed the lowest ICC values. With the exception of these two variables, 3D morphometrics showed “good” or “excellent” reliability. No significant difference in mean absolute difference was noted across imaging modalities for each morphometric feature. Conclusion The majority of 3D morphometric measures show “good” to “excellent” reliability across CTA, MRA, and DSA, allowing for comparison across imaging modalities.

Computational fluid dynamics and shape analysis enhance aneurysm rupture risk stratification

Article

Full-text available

Nov 2024

Purpose Accurately quantifying the rupture risk of unruptured intracranial aneurysms (UIAs) is crucial for guiding treatment decisions and remains an unmet clinical challenge. Computational Flow Dynamics and morphological measurements have been shown to differ between ruptured and unruptured aneurysms. It is not clear if these provide any additional information above routinely available clinical observations or not. Therefore, this study investigates whether incorporating image-derived features into the established PHASES score can improve the classification of aneurysm rupture status. Methods A cross-sectional dataset of 170 patients (78 with ruptured aneurysm) was used. Computational fluid dynamics (CFD) and shape analysis were performed on patients’ images to extract additional features. These derived features were combined with PHASES variables to develop five ridge constrained logistic regression models for classifying the aneurysm rupture status. Correlation analysis and principal component analysis were employed for image-derived feature reduction. The dataset was split into training and validation subsets, and a ten-fold cross validation strategy with grid search optimisation and bootstrap resampling was adopted for determining the models’ coefficients. Models’ performances were evaluated using the area under the receiver operating characteristic curve (AUC). Results The logistic regression model based solely on PHASES achieved AUC of 0.63. All models incorporating derived features from CFD and shape analysis demonstrated improved performance, reaching an AUC of 0.71. Non-sphericity index (shape variable) and maximum oscillatory shear index (CFD variable) were the strongest predictors of a ruptured status. Conclusion This study demonstrates the benefits of integrating image-based fluid dynamics and shape analysis with clinical data for improving the classification accuracy of aneurysm rupture status. Further evaluation using longitudinal data is needed to assess the potential for clinical integration.

Sex Differences in Intracranial Aneurysms: A Matched Cohort Study

Article

Full-text available

Sep 2024

Background: Aneurysmal subarachnoid hemorrhage (SAH) predominantly affects women, accounting for 65% of cases. Women have a 1.3 times higher relative risk than men, with the incidence rising particularly in women aged 55–85 years. Women also have a higher prevalence of unruptured intracranial aneurysms (IAs), especially after the age of 50 years, and are at greater risk of aneurysm growth and rupture. This study aimed to isolate the influence of sex on rupture rate, bleeding severity, functional outcomes, and complications by using a matched cohort, while also examining the impact of sex on aneurysm localization and multiplicity. Methods: We utilized a retrospectively collected database of 300 patients with 511 IAs. Inclusion criteria included the availability of clinical data and 3D angiography for semi-automatic reconstruction of IA morphology. Female patients and their IA were matched with male patients according to clinical parameters and 21 morphological characteristics using an interactive visual exploration tool for multidimensional matching. Results: Contrary to previously published results, our study found no significant sex differences in rupture rates or vasospasm rates between male and female patients. The severity of SAH, functional outcomes, and complications such as hydrocephalus were also similar in women and men. However, women exhibited a higher prevalence of multiple aneurysms and distinct localization patterns. Conclusion: This study underscores the complex role of sex in IA development and rupture. Although sex-specific biological factors influence aneurysm characteristics, they do not necessarily translate into differences in clinical outcomes. Further research is needed to explore these factors and their impact on aneurysm development and management.

Assessment of intracranial aneurysm neck deformation after contour deployment

Article

Full-text available

May 2024

Purpose The contour neurovascular system (CNS) is a novel device to treat intracranial wide-necked bifurcation aneurysms, with few studies assessing its long-term effects. Particularly its impact on aneurysm morphology has not been explored yet. We present a preliminary study to explore this impact for the first time, focusing on the neck curve and ostium of the aneurysm. Methods We investigated seven aneurysms treated with the CNS to assess ostium deformation after CNS deployment by comparing models extracted from in vivo medical pre-treatment and follow-up scans via morphological analysis. Time between pre- and follow-up scans was ten months on average. Size and shape indices like area, neck diameter, ellipticity index, undulation index, and more were assessed. Results Ostium size was reduced after treatment. On average, ostium area was reduced at a rate of

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- 0.58 (± 4.88) mm ² per year, from 15.52 (± 3.51) mm ² to 13.30 (± 2.27) mm ² , and ostium width from 5.01 (± 0.54) mm to 4.49 (± 0.45) mm, with an average reduction of

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- 0.59 (± 0.87) mm. This shrinking positively correlated with time passing. Shape deformation was low, though notably mean ellipticity index was reduced by 0.06 (± 0.15) on average, indicating ostia were less elongated after treatment. Conclusion We interpret the shrinking of the ostium as part of the healing process. Shape changes were found to be small enough to conclude no shape deformation of the ostium from CNS deployment, but the analysis of more cases with more parameters and information is necessary.

Visualization, Classification, and Interaction for Risk Analysis and Treatment Planning of Cerebral Aneurysms

Thesis

Full-text available

May 2019

Monique Meuschke

Cerebral aneurysms are weak vessel areas that can bulge out and balloon, caused by a pathologically altered structure of the vascular wall. They bear the risk of rupture, leading to internal bleeding causing high risks of mortality. Although most aneurysms will never rupture, the potential risk of bleeding makes the detection and risk-assessment of aneurysms a critical issue. Imaging methods are used for the detection and localization of aneurysms. The decision as to whether or not aneurysms should be treated must be carefully considered, as there is a risk of fatal outcome during surgery. Their initiation and progression depend strongly on the interplay of vascular morphology and hemodynamics. Unfortunately, the processes causing aneurysm growth and rupture are not well understood. Blood flow simulations can obtain information about the patient-specific hemodynamics. It is also the basis for the development for new, low-risk treatment options since treatment success depends on blood flow characteristics. In clinical routine, risk assessment and treatment planning are just based on morphological characteristics of an aneurysm and its surrounding vasculature. However, this information allows no reliable evaluation of the aneurysm state. To improve decision-making, medical and biomedical researchers analyze simulated flow data, which are multi-attribute data with high spatial and temporal complexity. The data exploration is performed quantitatively and qualitatively, where the former focuses on the evaluation of specific scalar values such as pressure or wall thickness and the latter focuses on the analysis of flow patterns such as vortices. Correlations between qualitative and quantitative characteristics can be revealed and formed into hypotheses that can lead to a better understanding of the internal aneurysm procedures. However, the visual exploration of flow data is a time-consuming process, which is affected by visual clutter and occlusions. The goal of our work is to develop computer-aided methods that support the quantitative and qualitative visual exploration of morphological and hemodynamic characteristics in cerebral aneurysm data sets. Since this is an interdisciplinary process involving both physicians and fluid mechanics experts, redundancy-free management of aneurysm data sets is required to enable efficient analysis of the information. We developed a consistent structure to document aneurysm data sets, where users can search for specific cohorts, and individual cases can be analyzed more detailed to assess the aneurysm state as well as to weigh different treatment scenarios. The prerequisite for the visual exploration is the extraction of the ostium, which is a curved surface that separates the parent vessel from an aneurysm. We provide an automatic determination of the ostium. Based on this several other morphological descriptors are computed automatically. Besides an analysis of morphological aspects, the aneurysm data exploration comprises four more parts: a simultaneous evaluation of wall- and flow-related characteristics, a simultaneous analysis of multiple scalar information on the aneurysm wall, the analysis of mechanical wall processes as well as a qualitative characterization of the internal flow behavior. We provide methods for each of these parts: occlusion-free depictions of the vessel morphology and internal blood flow, interactive 2D and 3D visualizations to explore multi-attribute correlations, comparative glyph-based visualizations to explore mechanical wall forces and automatic classification of qualitative flow patterns. Our methods were designed and evaluated in collaboration with domain experts who confirmed their usefulness and clinical necessity.

A deep-learning method for the end-to-end prediction of intracranial aneurysm rupture risk

Article

Full-text available

Mar 2023

The bigger picture An intracranial aneurysm (IA) is a pathological expansion of a weak area of a blood vessel wall in the brain because of the long-term effects of abnormal blood flow. Epidemiological estimates suggest that approximately 3% of the population has an intracranial aneurysm. While rupture is rare (occurring in less than 1% of cases), a ruptured IA has a high chance of leading to death. Treatments such as endovascular coiling, a technique that involves navigating a tiny wire coil into the aneurysm, and surgical clipping can reduce the risk of rupture but carry their own risks, including possible death. There is hope that artificial intelligence combined with advanced medical imaging techniques may be able to better identify IAs at high risk of rupture to help prioritize use of these treatments. Here, we describe a machine-learning technique we developed to predict rupture risk from 3D computed tomography angiography data, a medical imaging technique that involves injecting dyes into the blood and then imaging vascular features via X-ray and computational reconstruction. We show that this machine-learning method performs better than human-based predictions within our test datasets, and we hope that this work and others like it will help eventually move these methods into clinical practice, improving treatment outcomes for patients with IA.

Clinical Characteristics and Morphological Parameters Associated with Rupture of Anterior Communicating Artery Aneurysms

Article

Full-text available

Aug 2022
ACTA CLIN CROAT

Filip Vitošević

We analyzed aneurysm morphology, demographic and clinical characteristics in patients with anterior communicating artery (ACoA) aneurysms to investigate the risk factors contributing to aneurysm rupture. A total of 219 patients with ACoA aneurysms were admitted to our hospital between January 2016 and December 2020, and morphological and clinical characteristics were analyzed retrospectively in 153 patients (112 ruptured and 41 unruptured). Medical records were reviewed to obtain demographic and clinical data on age, gender, presence of hemorrhage, history of hypertension, diabetes, heart disease, and kidney disease. Morphological parameters examined on 3-dimensional digital subtraction angiography included aneurysm size, neck diameter, aspect ratio, size ratio, bottleneck ratio, height/width ratio, aneurysm angle, (in)flow angle, branching angle, number of aneurysms per patient, shape of the aneurysm, aneurysm wall morphology, variation of the A1 segment, and direction of the aneurysm. Male gender, aspect ratio, height/width ratio, non-spherical and irregular shape were associated with higher odds of rupture, whilst controlled hypertension was associated with lower odds of rupture, when tested using univariate logistic regression model. In multivariate model, controlled hypertension, presence of multiple aneurysms, and larger neck diameter reduced the odds of rupture, while irregular wall morphology increased the risk of rupture. Regulated hypertension represented a significant protective factor from ACoA aneurysm rupture. We found that ACoA aneurysms in male patients and those with greater aspect ratios and height/width ratios, larger aneurysm angles, presence of daughter sacs and irregular and non-spherical shapes were at a higher risk of rupture.

Morphological Characteristics of Ruptured Brain Aneurysms: A Systematic Literature Review and Meta‐Analysis

Article

Jan 2023

BACKGROUND It is unclear what morphological features of brain aneurysms are better at predicting risk of rupture. We conducted a meta‐analysis to analyze the best morphological determinants of rupture status. METHODS The Nested Knowledge platform was used to perform a search of articles reporting on aneurysm size, aspect ratio (AR), size ratio (SR), ellipticity index, nonsphericity index, and undulation index. The mean differences between ruptured and unruptured aneurysms were used to calculate effect sizes. RESULTS A total of 63 studies with 13 025 aneurysms were included: 6966 ruptured aneurysms and 6059 unruptured aneurysms. Ruptured aneurysms had a larger size ( P <0.001), AR ( P <0.001), SR ( P <0.001), ellipticity index ( P =0.049), and nonsphericity index ( P =0.049) compared with unruptured aneurysms. The mean size of ruptured aneurysms was 6.1 mm (95% CI, 5.6–6.5). The size of ruptured and unruptured aneurysms was similar in the anterior cerebral artery ( P =0.28), anterior communicating artery ( P =0.31), and basilar artery ( P =0.51). The mean AR of ruptured aneurysms was 1.5 (95% CI, 1.4–1.6), and the mean SR was 2.3 (95% CI, 2.1–2.5). For mirror aneurysms, the mean AR was 1.2 (95% CI, 1.2–1.5), and the mean SR was 2.2 (95% CI, 2.1–2.5). CONCLUSIONS Size is not significantly different between ruptured and unruptured aneurysms located in the anterior cerebral artery, anterior communicating artery, and basilar artery. SR is significantly different between ruptured and unruptured aneurysms in all locations. A mean AR of 1.5 and SR of 2.3 are the thresholds associated with ruptured aneurysm status.

A comprehensive investigation of morphological features responsible for cerebral aneurysm rupture using machine learning

Article

Full-text available

Jul 2024

Cerebral aneurysms are a silent yet prevalent condition that affects a significant global population. Their development can be attributed to various factors, presentations, and treatment approaches. The importance of selecting the appropriate treatment becomes evident upon diagnosis, as the severity of the disease guides the course of action. Cerebral aneurysms are particularly vulnerable in the circle of Willis and pose a significant concern due to the potential for rupture, which can lead to irreversible consequences, including fatality. The primary objective of this study is to predict the rupture status of cerebral aneurysms. To achieve this, we leverage a comprehensive dataset that incorporates clinical and morphological data extracted from 3D real geometries of previous patients. The aim of this research is to provide valuable insights that can help make informed decisions during the treatment process and potentially save the lives of future patients. Diagnosing and predicting aneurysm rupture based solely on brain scans is a significant challenge with limited reliability, even for experienced physicians. However, by employing statistical methods and machine learning techniques, we can assist physicians in making more confident predictions regarding rupture likelihood and selecting appropriate treatment strategies. To achieve this, we used 5 classification machine learning algorithms and trained them on a substantial database comprising 708 cerebral aneurysms. The dataset comprised 3 clinical features and 35 morphological parameters, including 8 novel morphological features introduced for the first time in this study. Our models demonstrated exceptional performance in predicting cerebral aneurysm rupture, with accuracy ranging from 0.76 to 0.82 and precision score from 0.79 to 0.83 for the test dataset. As the data are sensitive and the condition is critical, recall is prioritized as the more crucial parameter over accuracy and precision, and our models achieved outstanding recall score ranging from 0.85 to 0.92. Overall, the best model was Support Vector Machin with an accuracy and precision of 0.82, recall of 0.92 for the testing dataset and the area under curve of 0.84. The ellipticity index, size ratio, and shape irregularity are pivotal features in predicting aneurysm rupture, respectively, contributing significantly to our understanding of this complex condition. Among the multitude of parameters under investigation, these are particularly important. In this study, the ideal roundness parameter was introduced as a novel consideration and ranked fifth among all 38 parameters. Neck circumference and outlet numbers from the new parameters were also deemed significant contributors.

A novel parameter for the prediction of rupture risk of cerebral aneurysms based on morphology

Article

Aug 2023
P I MECH ENG H

Neurosurgeons often encounter dilemmas in the clinical management of cerebral aneurysms owing to an uncertainty of their rupture status and rupture risk. This study evaluates the influence of natural frequency of an aneurysm, as a novel morphological parameter to understand and analyze rupture status and risk prediction. In this work, we employ the natural frequency of 20 idealized and 50 patient specific aneurysms. The natural frequency of patient specific aneurysms is then compared against their rupture status. A strong correlation was observed between various morphological indicators and natural frequency for ideal and patient specific geometries. A statistical analysis with both Mann Whitney U test and T-test for rupture status against natural frequency has given a p-value less than 0.01 indicating a strong correlation between them. The correlation of morphological parameters with natural frequency from Pearson correlation coefficient and T-test suggests a holistic reflection of their effects on the natural frequency of an aneurysm. Thus, natural frequency could be a good indicator to discern the rupture potential of an aneurysm. The correlation between rupture status and natural frequency makes it a novel parameter that can differentiate between ruptured and unruptured patient specific aneurysms.

On the major role played by the lumen curvature of intracranial aneurysms walls in determining their mechanical response, local hemodynamics, and rupture likelihood

Article

Jun 2023
COMPUT BIOL MED

The properties of intracranial aneurysms (IAs) walls are known to be driven by the underlying hemodynamics adjacent to the IA sac. Different pathways exist explaining the connections between hemodynamics and local tissue properties. The emergence of such theories is essential if one wishes to compute the mechanical response of a patient-specific IA wall and predict its rupture. Apart from the hemodynamics and tissue properties, one could assume that the mechanical response also depends on the local morphology, more specifically, the curvature of the luminal surface, with larger values at highly-curved wall portions. Nonetheless, this contradicts observations of IA rupture sites more often found at the dome, where the curvature is lower. This seeming contradiction indicates a complex interaction between the hemodynamics adjacent to the aneurysm wall, its morphology, and mechanical response, which warrants further investigation. This was the main goal of this work. We accomplished this by analysing the stress and stretch fields in different regions of the wall for a sample of IAs, which have been classified based on particular hemodynamics conditions and lumen curvature. Pulsatile numerical simulations were performed using the one-way fluid-solid interaction strategy implemented in OpenFOAM (solids4foam toolbox). We found that the variable best correlated with regions of high stress and stretch was the lumen curvature. Additionally, our data suggest a connection between the local curvature and particular hemodynamics conditions adjacent to the wall, indicating that the lumen curvature is a property that could be used to assess both mechanical response and hemodynamic conditions, and, moreover, suggest new rupture indicators based on the curvature.

Comparison of Morphological Profiles between Aneurysms of Anterior and Posterior Cerebral Circulation of Sub Arachnoid Haemorrhage Patients

Article

Full-text available

Dec 2020

Background: Intracranial aneurysms (IAs) of the posterior circulation (PC) rupture more frequently and the morbidity and mortality rates are higher compared to anterior circulation. Morphological parameters such as dome neck width, size ratio (SR), believed to contribute significantly in determining the risk of rupture of intracranial aneurysms. Aims: To compare the morphometry of ruptured aneurysms between anterior and posterior circulation aneurysm in aneurysmal Subarachnoid haemorrhage (aSAH) patients. Methods: This analytical cross-sectional study was carried out in the department neurologyof National Institute of Neurosciences and Hospital, Dhaka. A total 110 patients of aneurysmal SAH confirmed by non-contrast CT scan of head having age more than 18 years, of both sexes and who gave consent were enrolled in this study. Morphologic parameter like neck width, maximum dome diameter(SR) and locations were recorded in the data collection sheet. Results: A total number of 110 patients were recruited after fulfilling inclusion and exclusion criteria. Of them two had normal findings in digital subtraction angiogram(DSA). Majority (31.5%) of the patients belonged to age group 50-59 years. Male and female ratio was 1:1.25. Regarding the morphology of aneurysm, 96 patients had aneurysm in anterior cerebral circulation and 12 patients had aneurysms in posterior cerebral circulation. Most of the aneurysms of anterior and posterior cerebral circulation were saccular in type. Fusiform aneurysms were found 3(3.1%) and 2(16.7%) in anterior and posterior cerebral circulation respectively with p value of 0.035. The mean neck width was 2.92±1.52 mm in anterior and 5.96±5.72 mm in posterior cerebral circulation(p<0.05). Conclusion: This study revealed neck width is found to be significant differentiating factor between intracerebral aneurysms of anterior and posterior cerebral circulation. Fusiform aneurysm is significantly higher in posterior circulation. There is no significant difference in clinical profile of patients of anterior and posterior circulation.

Near-Wall Slow Flow Contributes to Wall Enhancement of Middle Cerebral Artery Bifurcation Aneurysms on Vessel Wall MRI

Article

Full-text available

Dec 2024

Background: The mechanism of aneurysm wall enhancement (AWE) in middle cerebral artery (MCA) bifurcation aneurysms on vessel wall magnetic resonance imaging (VW-MRI) remains unclear. We aimed to explore the morphologically related hemodynamic mechanism for the AWE of MCA bifurcation aneurysms. Methods: Patients with unruptured MCA bifurcation aneurysms undergoing VW-MRI were enrolled. Logistic regression analyses were performed to determine the risk factors for AWE. Based on the results of retrospective analyses, bifurcation aneurysm silicone models with a specific aspect ratio (AR) were designed and underwent VW-MRI with different inlet velocities. Computational fluid dynamics (CFD) analyses were conducted on both silicone models and patients’ aneurysms. Results: A total of 104 aneurysms in 95 patients (mean age 60; 34 males) were included for baseline analysis and morphological analysis. Logistic regression analysis indicated AR (OR, 5.92; 95% CI, 2.00–17.55; p = 0.001) was associated with AWE. In the high-AR group of 45 aneurysms with AWE, the aneurysm sac exhibited lower blood flow velocity, lower wall shear stress, a larger proportion of low-flow regions and higher wall enhancement values. In total, 15 silicone models were analyzed, divided into three subgroups based on neck width (4 mm, 6 mm, and 8 mm). Each subgroup contained aneurysms with five different ARs: 1.0, 1.25, 1.5, 1.75, and 2.0. In silicone models, contrast enhancement (CE) was mainly located beneath the dome of the aneurysm wall. With the same inlet velocity, CE gradually increased as the AR increased. Similarly, at the same AR, CE increased as the inlet velocity decreased. CFD demonstrated a moderate positive correlation between the near-wall enhancement index and the ratio of the low-velocity area (r = 0.6672, p < 0.001). Conclusions: The AR is associated with the AWE of MCA bifurcation aneurysms. A high AR may promote wall enhancement by causing near-wall slow flow.

In Vivo Deformation of the Human Basilar Artery

Article

Full-text available

Aug 2024
ANN BIOMED ENG

An estimated 6.8 million people in the United States have an unruptured intracranial aneurysms, with approximately 30,000 people suffering from intracranial aneurysms rupture each year. Despite the development of population-based scores to evaluate the risk of rupture, retrospective analyses have suggested the limited usage of these scores in guiding clinical decision-making. With recent advancements in imaging technologies, artery wall motion has emerged as a promising biomarker for the general study of neurovascu-lar mechanics and in assessing the risk of intracranial aneurysms. However, measuring arterial wall deformations in vivo itself poses several challenges, including how to image local wall motion and deriving the anisotropic wall strains over the cardiac cycle. To overcome these difficulties, we first developed a novel in vivo MRI-based imaging method to acquire cardiac gated images of the human basilar artery (BA) over the cardiac cycle. Next, complete BA endoluminal surfaces from each frame were segmented, producing high resolution point clouds of the endoluminal surfaces. From these point clouds we developed a novel B-spline based surface representation, then exploited the local support nature of B-splines to determine the local endoluminal surface strains. Results indicated distinct regional and temporal variations in BA wall deformation, highlighting the heterogeneous nature BA function. These included large circumferential strains (up to ∼ 20 %), and small longitudinal strains, which were often contractile and out of phase with the circumferential strains patterns. Of particular interest were the temporal phase lag in the maximum circumferential perimeter length, which indicated that the BA deforms asynchronously over the cardiac cycle. In summary, the proposed method enabled local deformation analysis, allowing for the successful reproduction of local features of the BA, such as regional principal stretches, areal changes and pulsatile motion. Integrating the proposed method into existing population-based scores has the potential to improve our understanding of mechanical properties of human BA and enhance clinical decision-making. 2

AnXplore: a comprehensive fluid-structure interaction study of 101 intracranial aneurysms

Article

Full-text available

Jun 2024

Advances in computational fluid dynamics continuously extend the comprehension of aneurysm growth and rupture, intending to assist physicians in devising effective treatment strategies. While most studies have first modelled intracranial aneurysm walls as fully rigid with a focus on understanding blood flow characteristics, some researchers further introduced Fluid-Structure Interaction (FSI) and reported notable haemodynamic alterations for a few aneurysm cases when considering wall compliance. In this work, we explore further this research direction by studying 101 intracranial sidewall aneurysms, emphasizing the differences between rigid and deformable-wall simulations. The proposed dataset along with simulation parameters are shared for the sake of reproducibility. A wide range of haemodynamic patterns has been statistically analyzed with a particular focus on the impact of the wall modelling choice. Notable deviations in flow characteristics and commonly employed risk indicators are reported, particularly with near-dome blood recirculations being significantly impacted by the pulsating dynamics of the walls. This leads to substantial fluctuations in the sac-averaged oscillatory shear index, ranging from −36% to +674% of the standard rigid-wall value. Going a step further, haemodynamics obtained when simulating a flow-diverter stent modelled in conjunction with FSI are showcased for the first time, revealing a 73% increase in systolic sac-average velocity for the compliant-wall setting compared to its rigid counterpart. This last finding demonstrates the decisive impact that FSI modelling can have in predicting treatment outcomes.

Rupture Predictive Factors for Intracranial Aneurysms

Article

Full-text available

Jun 2023
Rev Cubana Med

Introducción: Un aneurisma intracraneal roto provoca una hemorragia subaracnoidea. La enfermedad presenta una alta mortalidad y morbilidad. Sin embargo, no todos se rompen. Mejorar la predicción de rotura permitirá un tratamiento quirúrgico preventivo en un grupo de pacientes y evitará una intervención quirúrgica con riesgos en otro grupo de enfermos. Es necesario identificar factores predictivos para mejorar la estratificación del riesgo de rotura y optimizar el tratamiento de los aneurismas intracraneales incidentales. Objetivo: Identificar factores predictivos de rotura de aneurismas intracraneales. Métodos: En una muestra de 152 pacientes espirituanos con aneurismas intracraneales saculares rotos (n = 138) y no rotos (n = 22) y 160 imágenes de angiografía por tomografía computarizada, se realizaron mensuraciones de los índices o factores morfológicos, los cuales se combinaron mediante análisis de regresión logística con variables demográficas y clínicas. Resultados: El grupo de edad con mayor frecuencia de presentación de aneurismas fue el de mayor de 65 años. La muestra estuvo representada, en su gran mayoría, por el sexo femenino. Se identificaron tres factores clínicos y cuatro factores morfológicos estadísticamente significativos, asociados con la rotura. El índice de no esfericidad (p = 0,002 y el sexo femenino (p = 0,02) fueron los de mayor significación estadística. Conclusiones: Se detectaron siete factores predictivos de rotura de aneurismas intracraneales estadísticamente significativos, de los cuales el índice de no esfericidad resultó el de mayor significación.

Plasma levels of CD36 and glutathione as biomarkers for ruptured intracranial aneurysm

Article

Full-text available

Dec 2023

Evidence has proved that intracranial aneurysm (IA) formation and rupture might be closely related to inflammatory response and oxidative stress. Our objective was to evaluate the potential of CD36 and glutathione (GSH) as biomarkers for IA. In this study, the enzyme-linked immunosorbent assay was used to measure the plasma levels of CD36 and GSH in 30 IA patients and 30 healthy controls. Then, correlation analysis, receiver operating characteristic (ROC) curve, and logistic regression analysis were performed. The results showed that the plasma level of CD36 in IA patients was significantly higher than that in the control group (P < 0.0001), and plasma GSH was significantly lower compared with that in the control group (P < 0.0001). ROC analysis showed that CD36 and GSH had high sensitivity (90.0 and 96.6%) and specificity (96.6 and 86.6%) for IA diagnosis. The combined sensitivity and specificity achieved were 100 and 100%, respectively. The plasma levels of CD36 and GSH did not show a significant correlation with age, the Glasgow Coma Scale, Hunter-Hess score, aneurysm size, aneurysm height, aneurysm neck, and aspect ratio. The AUC of the logistic regression model based on CD36 and GSH was 0.505. Our results suggested that the combination of plasma CD36 and GSH could serve as potential biomarkers for IA rupture.

On software tools and variability in medical image-based computational fluid dynamics

Thesis

Full-text available

May 2023

Aslak Bergersen

Evaluation of unruptured aneurysm scoring systems and ratios in subarachnoid hemorrhage patients with multiple intracranial aneurysms

Article

Full-text available

Oct 2023

Background: This study aims to appraise aneurysm scores and ratios’ ability to discriminate between ruptured aneurysms and unruptured intracranial aneurysms (UIAs) in subarachnoid hemorrhage (SAH) patients harboring multiple intracranial aneurysms (MICAs). We, then, investigate the most frequent risk factors associated with MICAs. Methods: We retrospectively applied unruptured intracranial aneurysm treatment score (UIATS) and population hypertension age size of aneurysm earlier SAH from another aneurysm site of aneurysm (PHASES) score, aspect, and dome-to-neck ratio to the 59 consecutive spontaneous SAH patients with MICAs admitted between January 2000 and December 2015 to the Department of Neurosurgery of the University Hospital Center “Hôpital des Spécialités” of Rabat (Morocco). Patients with at least two intracranial aneurysms (IAs) confirmed on angiography were included in the study. Results: Fifty-nine patients were harboring 128 IAs. The most frequent patient-level risk factors were arterial hypertension (AHT) 30.5 % (n = 18) and smoking status 22.0 % (n = 13). A PHASES score recommended treatment in 52 of 60 ruptured aneurysms and in six of 68 UIAs with a sensitivity of 31.67% and a specificity of 76.47%. UIATS recommended treatment in 26 of 62 ruptured aneurysms and in 35 of 55 UIAs with a sensitivity of 41.9% and a specificity of 63.6%. Aspect ratio recommended treatment in 60 of 60 ruptured aneurysms and in 63 of 68 UIAs with a sensitivity of 100% and a specificity of 88.24%. Dome-to-neck ratio recommended treatment in 45 of 60 ruptured aneurysms and in 48 of 68 UIAs with a sensitivity of 80% and a specificity of 63.24%. The aspect ratio (area under the curve [AUC] = 0.953) AUC > 0.8 has a higher discriminatory power between ruptured aneurysms and UIAs. Conclusion: AHT and smoking status were the most common risk factors for intracranial multiple aneurysms and the aspect ratio and PHASES score were the most powerful discrimination tools between ruptured aneurysms and the UIAs. Keywords: Multiple intracranial aneurysms, Ruptured aneurysm, Scores and ratio, Unruptured aneurysm

Antiplatelets, Anticoagulation, and Elective Aneurysm Treatment in Neuro patients

Article

Full-text available

Oct 2023

Developing more specialized care for neurological disorders, such as aneurysms, arteriovenous malformations, and strokes, can revolutionize patient healthcare and outcomes. With the advent of surgical techniques such as flow diversion, non-stent- and stent-assisted coiling, and catheter embolization for elective aneurysm treatment in neurological patients, the adverse effects and morbidities associated with aneurysms can be reduced. This paper aims to highlight three specific strengths and weaknesses of the newly emerged techniques. Flow diversion devices involve placing a stent in the parent artery, whereas Woven EndoBridge embolization involves manipulation of the wall of the artery without the administration of dual-antiplatelet therapy. In addition to aneurysm treatment, the administration of antiplatelets and anticoagulants is helpful in disrupting the coagulation cascade. As stated in the new and enhanced guidelines released by the American Heart Association, the administration of dual anticoagulants is beneficial to the patients if they have low ischemic severity. Understanding the various benefits and complications associated with each treatment can allow clinicians to gain insight into the potential trajectory of treatment for different patients.

Morphological characteristics of brain aneurysms among age groups

Article

Sep 2023

Background Patient's age is an important factor in determining the risk of aneurysm rupture. However, there is limited data on how aneurysm morphology differs among age groups. We studied morphological characteristics of brain aneurysms among age groups in a large cohort. Methods Aneurysms from the Stroke Thrombectomy and Aneurysm Registry (STAR) were analyzed. The following parameters were included: location, size, neck, width, height, aspect ratio, and regular versus irregular morphology. The risk of rupture presentation was estimated using logistic regression. Results A total of 1407 unruptured and 607 ruptured saccular aneurysms were included. The most common locations of ruptured aneurysms in patients younger than 70 years-old were the middle cerebral artery (MCA) and the anterior communicating artery (ACOM). The most common location of ruptured aneurysms in patients older than 70 years-old were the posterior communicating artery (PCOM) and ACOM. The size of unruptured aneurysms increased with age (p < .001). Conversely, the size of ruptured aneurysms was similar among age groups (p = .142). Unruptured and ruptured aneurysms became more irregular at presentation with older age (p < .001 and p .025, respectively). Irregular morphology and location were associated with rupture status across all age groups in multivariate regression. Conclusions Younger patients have small unruptured and ruptured aneurysms, and ruptured aneurysms are mostly located in the MCA and ACOM. Older patients have larger and more irregular unruptured aneurysms, and ruptured aneurysms are mostly located in the PCOM and ACOM. An irregular morphology increases the risk of rupture in all age groups.

Influence of morphological characteristics on the deposition of low-density lipoprotein in intracranial bifurcation aneurysms

Article

Aug 2023

The increasingly demonstrated association of wall enhancement (WE) measured by vascular wall imaging with the instability/rupture of intracranial aneurysms (IAs) implies the significance of investigating the transport and accumulation of blood substances [e.g., low-density lipoprotein (LDL), lipoprotein (a)] related to WE in IAs. In the present study, we perform numerical simulations to explore the relationships between the distribution/severity of LDL deposition on the lumen surface and the morphological characteristics of aneurysm and its adjacent arteries as well as the underlying fluid dynamic mechanisms. Bifurcation aneurysms located at the middle cerebral artery are selected as the subject of investigation and for which both idealized and patient-specific models are built. Studies on the idealized models reveal that the aneurysm–parent (AP) artery angle is more powerful than other morphological parameters [e.g., daughter–parent (DP) artery angle, nonsphericity index (NI) of aneurysm] in determining the severity of LDL deposition. A bleb (i.e., secondary sac) can enhance local LDL deposition, especially when located in an LDL deposition-prone aneurysm wall region. In patient-specific models, the dominant effect on the LDL deposition of the AP angle remains identifiable, whereas the effects of the DP angle and NI are overwhelmed by confounding factors. Enhanced LDL deposition prefers to appear in wall regions perpendicular to the intra-aneurysmal vortex centerline. In comparison with wall shear stress magnitude, the normal-to-tangential near-wall velocity ratio and particle residence time can better predict the localization of enhanced LDL deposition.

The Current Limitations and Advanced Analysis of Hemodynamic Study of Cerebral Aneurysms

Article

Full-text available

Jun 2023

Kwang-Chun Cho

Among the various perspectives on cerebrovascular diseases, hemodynamic analysis-which has recently garnered interest-is of great help in understanding cerebrovascular diseases. Computational fluid dynamics (CFD) analysis has been the primary hemodynamic analysis method, and studies on cerebral aneurysms have been actively conducted. However, owing to the intrinsic limitations of the analysis method, the role of wall shear stress (WSS), the most representative parameter, remains controversial. High WSS affects the formation of cerebral aneurysms; however, no consensus has been reached on the role of WSS in the growth and rupture of cerebral aneurysms. Therefore, this review aimed to briefly introduce the up-to-date results and limitations made through CFD analysis and to inform the need for a new hemodynamic analysis method.

Deep learning-based recognition and segmentation of intracranial aneurysms under small sample size

Article

Full-text available

Dec 2022

The manual identification and segmentation of intracranial aneurysms (IAs) involved in the 3D reconstruction procedure are labor-intensive and prone to human errors. To meet the demands for routine clinical management and large cohort studies of IAs, fast and accurate patient-specific IA reconstruction becomes a research Frontier. In this study, a deep-learning-based framework for IA identification and segmentation was developed, and the impacts of image pre-processing and convolutional neural network (CNN) architectures on the framework’s performance were investigated. Three-dimensional (3D) segmentation-dedicated architectures, including 3D UNet, VNet, and 3D Res-UNet were evaluated. The dataset used in this study included 101 sets of anonymized cranial computed tomography angiography (CTA) images with 140 IA cases. After the labeling and image pre-processing, a training set and test set containing 112 and 28 IA lesions were used to train and evaluate the convolutional neural network mentioned above. The performances of three convolutional neural networks were compared in terms of training performance, segmentation performance, and segmentation efficiency using multiple quantitative metrics. All the convolutional neural networks showed a non-zero voxel-wise recall (V-Recall) at the case level. Among them, 3D UNet exhibited a better overall segmentation performance under the relatively small sample size. The automatic segmentation results based on 3D UNet reached an average V-Recall of 0.797 ± 0.140 (3.5% and 17.3% higher than that of VNet and 3D Res-UNet), as well as an average dice similarity coefficient (DSC) of 0.818 ± 0.100, which was 4.1%, and 11.7% higher than VNet and 3D Res-UNet. Moreover, the average Hausdorff distance (HD) of the 3D UNet was 3.323 ± 3.212 voxels, which was 8.3% and 17.3% lower than that of VNet and 3D Res-UNet. The three-dimensional deviation analysis results also showed that the segmentations of 3D UNet had the smallest deviation with a max distance of +1.4760/−2.3854 mm, an average distance of 0.3480 mm, a standard deviation (STD) of 0.5978 mm, a root mean square (RMS) of 0.7269 mm. In addition, the average segmentation time (AST) of the 3D UNet was 0.053s, equal to that of 3D Res-UNet and 8.62% shorter than VNet. The results from this study suggested that the proposed deep learning framework integrated with 3D UNet can provide fast and accurate IA identification and segmentation.

Hémorragie intracérébrale spontanée : développement d’un traitement pour les accidents vasculaires cérébraux hémorragiques et physiopathologie de l’anévrisme intracérébral

Thesis

Sep 2021

Estelle Roxanne Louet

Les hémorragies cérébrales spontanées sont donc un besoin médical non satisfait. Une des stratégies pour leur traitement est le retrait de l’hématome en utilisant un thrombolytique couplé à une intervention minimisant le risque d'endommager le tissu cérébral. Mon projet de thèse était de travailler au développement d'un nouveau produit alliant un thrombolytique de nouvelle génération couplée à une formulation à relargage progressif. Les résultats obtenus ont permis de démontrer la preuve de concept pour l'utilisation d’une formulation à relargage progressif d’un thrombolytique afin d'obtenir une lyse optimale, de démontrer la supériorité de l’O2L-001 et de ce fait, un nouvel espoir pour le traitement des hémorragies intracérébrales.La rupture des anévrismes intracrâniens est la cause la plus commune des hémorragies sous-arachnoïdiennes non traumatiques. À l'heure actuelle, les seules options de traitement possibles sont des interventions chirurgicales avec des risques non négligeables. Une meilleure compréhension de leur physiopathologie est donc cruciale pour l’amélioration du traitement des patients. Il a précédemment été démontré que l’activateur tissulaire du plasminogène pouvait être impliqué dans cette pathologie. Dans ce travail de thèse, je me suis focalisée sur la compréhension des mécanismes par lesquels l’activateur tissulaire du plasminogène était impliqué dans cette pathologie. Les résultats obtenus dans mes travaux de thèse ont permis de mettre en évidence l'interaction tPA-NMAR dans la formation et la rupture des anévrismes. De plus l’utilisation du Glunomab® permet de réduire l’incidence des anévrismes et leur rupture, ouvrant de nouvelles perspectives de traitement dans cette pathologie.

Evaluation of plasma CD36 and glutathione as potential biomarkers for intracranial aneurysm.

Preprint

Full-text available

Dec 2022

The underlying mechanisms of intracranial aneurysm (IA) formation and rupture are still unclear. Evidence has proved that it might be closely related to inflammatory response and oxidative stress. Our objective was to identify novel inflammatory and oxidative stress related biomarkers to assist IA management. In this study, the enzyme-linked immunosorbent assay was performed to measure the expression levels of CD36 and glutathione (GSH) in the plasma of 30 IA patients and 30 healthy controls. Then, correlation analysis and receiver operating characteristic (ROC) curve, and logistic regression analysis were applied to investigate CD36 and GSH as potential biomarker for IA. The expression level of plasma CD36 in the IA patients was significantly higher than that in the control group (P < 0.0001), and the level of plasma GSH in the IA patients was significantly lower than that in the control group (P < 0.0001). The plasma level of CD36 and GSH did not show significant correlation with age, Glasgow Coma Scale (GCS), Hunter-Hess score, aneurysm size, aneurysm height, aneurysm neck, and aspect ratio. ROC analysis showed that CD36 and GSH had high sensitivity (90.0%, 96.6%) and specificity (96.6%, 86.6%) for IA diagnosis. And the combined sensitivity and specificity achieved 100% and 100%, respectively. The AUC of logistic regression model based on CD36 and GSH was 0.505. Our results suggested that CD36 and GSH might participate in the process of IA formation and rupture but did not affect its morphology. Moreover, the combination plasma CD36 and GSH could serve as potential biomarker for IA rupture.

Fluid structure Interaction analysis for rupture risk assessment in patients with middle cerebral artery aneurysms

Article

Full-text available

Jan 2025

Accurate rupture risk assessment is essential for optimizing treatment decisions in patients with cerebral aneurysms. While computational fluid dynamics (CFD) has provided critical insights into aneurysmal hemodynamics, most analyses focus on blood flow patterns, neglecting the biomechanical properties of the aneurysm wall. To address this limitation, we applied Fluid-Structure Interaction (FSI) analysis, an integrative approach that simulates the dynamic interplay between hemodynamics and wall mechanics, offering a more comprehensive risk assessment. In this study, we used advanced FSI techniques to investigate the rupture risk of middle cerebral artery bifurcation (MCA) aneurysms, analyzing a cohort of 125 patients treated for a MCA aneurysm at Kepler University Hospital, Linz, Austria. Multivariate analysis identified two significant rupture predictors: High Equivalent Stress Area (HESA; p = 0.049), which quantifies stress distribution relative to the aneurysm surface, and Gaussian curvature (GLN; p = 0.031), which captures geometric complexity. We also introduce the HGD index, a novel composite metric combining HESA, GLN, and Maximum Wall Displacement, designed to enhance predictive accuracy. With a threshold of 0.075, the HGD index exhibited excellent diagnostic performance; in internal validation, 24 of 25 ruptured aneurysms surpassed this threshold, yielding a sensitivity of 0.96. In a 5-fold cross validation the reliability of results was confirmed. Our findings demonstrate that the HGD index provides superior rupture risk stratification compared to conventional single-parameter models, offering a more robust tool for the assessment of complex aneurysmal structures. Further multicenter studies are warranted to refine and validate the HGD index, advancing its potential for clinical application and improving patient outcomes. Supplementary Information The online version contains supplementary material available at 10.1038/s41598-024-85066-9.

Anterior interhemispheric vs. pterional approach in the microsurgical management of anterior communicating artery aneurysms: a comparative analysis employing a novel multidimensional matching-tool

Article

Full-text available

Jul 2024
NEUROSURG REV

The surgical management of anterior communicating artery aneurysms (AcomA) is challenging due to their deep midline position and proximity to complex skull base anatomy. This study compares the pterional craniotomy with the interhemispheric approach based on the specific aneurysm angulation. A total of 129 AcomA cases were analyzed, with 50 undergoing microsurgical clipping via either the pterional or interhemispheric approach. All selected cases had computed tomography-angiography with sagittal imaging slices and 2D-angiography. Using an interactive tool, 14 cases treated via the interhemispheric approach were matched with 14 cases approached pterionally based on clinical and morphological parameters, emphasizing intracranial aneurysm (IA) dome angulation relative to the frontal skull base. Outcomes included IA occlusion, temporary clipping incidence, intraoperative rupture, postoperative strokes, hemorrhages, hydrocephalus, vasospasm, and patient functionality. Matched cohorts had consistent demographics. Both approaches resulted in similar IA occlusion rates, but the interhemispheric approach led to improved clinical outcomes, measured by the modified Rankin Scale. It also had a lower incidence of hydrocephalus and reduced need for permanent ventriculoperitoneal shunt placement. Vasospasms and postoperative infarction rates were comparable between the groups. Our findings suggest potential advantages of the interhemispheric approach in managing AcomA, depending on aneurysm angulation. Despite a small sample size, the results highlight the importance of customized surgical decision-making based on the unique traits of each aneurysm and the surgeon's expertise.

Computational study of effect of hybrid nanoparticles on hemodynamics and thermal transfer in ruptured arteries with pathological dilation

Article

Full-text available

Jun 2024

The intended research aims to explore the convection phenomena of a hybrid nanofluid composed of gold and silver nanoparticles. This research is novel and significant because there is a lack of existing studies on the flow behavior of hybrid nanoparticles with important physical properties of blood base fluids, especially in the case of sidewall ruptured dilated arteries. The implementation of combined nanoparticles rather than unadulterated nanoparticles is one of the most crucial elements in boosting the thermal conduction of fluids. The research methodology encompasses the utilization of advanced bio-fluid dynamics software for simulating the flow of the nanofluid. The physical context elucidates the governing equations of momentum, mass, momentum, and energy in terms of partial differential equations. The results are displayed in both tabular and graphical forms to demonstrate the numerical and graphical solutions. The effect of physical parameters on velocity distribution is illustrated through graphs. Furthermore, the study’s findings are unique and original, and these computational discoveries have not been published by any researcher before. The finding implies that utilizing hybrid nanoparticles as drug carriers holds great promise in mitigating the effects of blood flow, potentially enhancing drug delivery, and minimizing its impact on the body.

Assessing the Influence of Aneurysm Dimensions on Hemodynamic Patterns and Wall Deformation Dynamics for Predicting Rupture Risk

Article

Apr 2024

Combining Machine-Measured Morphometric, Geometric, and Hemodynamic Factors to Predict the Risk of Aneurysm Rupture at the Middle Cerebral Artery Bifurcation

Article

Feb 2024

Nomograms for assessing the rupture risk of anterior choroid artery aneurysms based on clinical, morphological, and hemodynamic features

Article

Full-text available

Feb 2024

Background and purpose A notable prevalence of subarachnoid hemorrhage is evident among patients with anterior choroidal artery aneurysms in clinical practice. To evaluate the risk of rupture in unruptured anterior choroidal artery aneurysms, we conducted a comprehensive analysis of risk factors and subsequently developed two nomograms. Methods A total of 120 cases of anterior choroidal artery aneurysms (66 unruptured and 54 ruptured) from 4 medical institutions were assessed utilizing computational fluid dynamics (CFD) and digital subtraction angiography (DSA). The training set, consisting of 98 aneurysms from 3 hospitals, was established, with an additional 22 cases from the fourth hospital forming the external validation set. Statistical differences between the two data sets were thoroughly compared. The significance of 9 clinical baseline characteristics, 11 aneurysm morphology parameters, and 4 hemodynamic parameters concerning aneurysm rupture was evaluated within the training set. Candidate selection for constructing the nomogram models involved regression analysis and variance inflation factors. Discrimination, calibration, and clinical utility of the models in both training and validation sets were assessed using area under curves (AUC), calibration plots, and decision curve analysis (DCA). The DeLong test, net reclassification index (NRI), and integrated discrimination improvement (IDI) were employed to compare the effectiveness of classification across models. Results Two nomogram models were ultimately constructed: model 1, incorporating clinical, morphological, and hemodynamic parameters (C + M + H), and model 2, relying primarily on clinical and morphological parameters (C + M). Multivariate analysis identified smoking, size ratio (SR), normalized wall shear stress (NWSS), and average oscillatory shear index (OSIave) as optimal candidates for model development. In the training set, model 1 (C + M + H) achieved an AUC of 0.795 (95% CI: 0.706 ~ 0.884), demonstrating a sensitivity of 95.6% and a specificity of 54.7%. Model 2 (C + M) had an AUC of 0.706 (95% CI: 0.604 ~ 0.808), with corresponding sensitivity and specificity of 82.4 and 50.3%, respectively. Similarly, AUCs for models 1 and 2 in the external validation set were calculated to be 0.709 and 0.674, respectively. Calibration plots illustrated a consistent correlation between model evaluations and real-world observations in both sets. DCA demonstrated that the model incorporating hemodynamic parameters offered higher clinical benefits. In the training set, NRI (0.224, p = 0.007), IDI (0.585, p = 0.002), and DeLong test (change = 0.089, p = 0.008) were all significant. In the external validation set, NRI, IDI, and DeLong test statistics were 0.624 (p = 0.063), 0.572 (p = 0.044), and 0.035 (p = 0.047), respectively. Conclusion Multidimensional nomograms have the potential to enhance risk assessment and patient-specific treatment of anterior choroidal artery aneurysms. Validated by an external cohort, the model incorporating clinical, morphological, and hemodynamic features may provide improved classification of rupture states.

Unveiling rupture risk and clinical outcomes in midline aneurysms: A matched cohort analysis investigating the impact of localization within the anterior or posterior circulation

Article

Full-text available

Feb 2024
NEUROSURG REV

Intracranial aneurysms (IAs) located in the anterior and posterior circulations of the Circle of Willis present differential rupture risks. This study aimed to compare the rupture risk and clinical outcomes of anterior communicating artery aneurysms (AcomA) and basilar tip aneurysms (BAs); two IA types located along the midline within the Circle of Willis. We retrospectively collected data from 1026 patients presenting with saccular IAs. Only AcomA and BAs with a 3D angiography were included. Out of 186 included IAs, a cohort of 32 BAs was matched with AcomA based on the patients’ pre-existing conditions and morphological parameters of IAs. Clinical outcomes, including rupture risk, hydrocephalus development, vasospasm incidence, and patients’ outcome, were compared. The analysis revealed no significant difference in rupture risk, development of hydrocephalus, need for ventricular drainage, or vasospasm incidence between the matched AcomA and BA cohorts. Furthermore, the clinical outcomes post-rupture did not significantly differ between the two groups, except for a higher Fisher Grade associated with BAs. Once accounting for morphological and patient factors, the rupture risk between AcomA and BAs is comparable. These findings underscore the importance of tailored management strategies for specific IA types and suggest that further investigations should focus on the role of individual patient and aneurysm characteristics in IA rupture risk and clinical outcomes.

Intracranial Aneurysms and Subarachnoid Hemorrhage

Chapter

Jan 2024

An aneurysm is an abnormal dilatation of an artery. In layman terms, an aneurysm can be thought of as a weak spot in the wall of an artery, similar to a garden hose that has been filed down on one side; water under pressure inside the hose will make the weak spot bulge out. Intracranial aneurysms can be broadly classified as saccular, fusiform, or dissecting. This chapter discusses the manifestations of the aneurysm and its treatment.

A Systematic Review and Meta-Analysis of 3-Dimensional Morphometric Parameters for Cerebral Aneurysms

Article

Dec 2023

Predictors for Rupture of Small (<7mm) Intracranial Aneurysms: A Systematic Review and Meta-Analysis

Article

Nov 2023

Introduction Identifying predictors for rupture of small intracranial aneurysms (sIAs) has become a growing topic in the literature given the relative paucity of data on their natural history. The authors performed a meta-analysis to identify reliable predictors. Methods PubMed, Scopus, and Web of Science were used to systematically extract references which involved at least 10 IAs <7mm which including a control group experiencing no rupture. All potential predictors reported in the literature were evaluated in the meta-analysis. Results Fifteen studies yielding 4739 sIAs were included in the meta-analysis. Four studies were prospective and 11 were retrospective. Univariate analysis identified 7 predictors which contradicted or are absent in the current scoring systems, while allowing to perform subgroup analysis for further reliability: patient age (MD -1.97, 95%CI -3.47--0.48; p = 0.01), the size ratio (MD 0.40, 95%CI 0.26-0.53; p < 0.00001), the aspect ratio (MD 0.16, 95%CI 0.11-0.22; p < 0.00001), bifurcation point (OR 3.76, 95%CI 2.41-5.85; p < 0.00001), irregularity (OR 2.95, 95%CI 1.91-4.55; p < 0.00001), the pressure loss coefficient (MD -0.32, 95%CI -0.52--0.11; p = 0.002), wall sheer stress (Pa) (MD -0.16, 95%CI -0.28--0.03; p = 0.01). All morphology related predictors listed above have been confirmed as independent predictors via multivariable analysis among the individual studies. Conclusions Morphology related predictors are superior to the classic patient demographic predictors present in most scoring systems. Given that morphology predictors take time to measure, our findings may be of great interest to developers seeking to incorporate artificial intelligence into the treatment decision-making process.

Numerical investigation of unruptured middle cerebral artery bifurcation aneurysms: influence of aspect ratio

Article

Nov 2023
COMPUT METHOD BIOMEC

An aneurysm is a disease condition, which is due to the pathological weakening of an arterial wall. These aneurysms are often found in various branch points and bifurcations of an artery in the cerebral circulation. Most aneurysms come to medical attention, either due to brain hemorrhages caused by rupture or found unruptured. To consider surgically invasive treatment modalities, clinicians need scientific methods such as, hemodynamic analysis to assess rupture risk. The arterial wall loses its structural integrity when wall shear stress (WSS) and other hemodynamic parameters exceed a certain threshold. In the present study, numerical simulations are carried out for unruptured middle cerebral artery (MCA) aneurysms. Three distinct representative sizes are chosen from a larger patient pool of 26 MCA aneurysms. Logically, these aneurysms represent three growth stages of any patient with similar anatomical structure. Simulations are performed to compare the three growth phases (with different aspect ratios) of an aneurysm and correlate their hemodynamic parameters. Simulations with patient specific boundary conditions reveal that, aneurysms with a higher aspect ratio (AR) correspond to an attendant decrease in both time-averaged wall shear stress (TAWSS) and spatial wall shear stress gradients (WSSG). Smaller MCAs were observed to have higher positive wall shear stress divergence (WSSD), exemplifying the tensile nature of arterial wall stretching. Present study identifies positive wall shear stress divergence (PWSSD) to be a potential biomarker for evaluating the growth of an aneurysm.

Frailty is a Predictor of Increased Readmissions and Increased Postoperative Complications After Elective Treatment of Unruptured Aneurysms

Article

Nov 2023

Hemodynamic and morphological differences in cerebral aneurysms between before and after rupture

Article

Full-text available

Sep 2023

Objective: Although it has been proposed that aneurysm morphology is different after rupture, detailed research of the morphological changes using 3D imaging acquired before and after rupture has not been conducted because of the difficulty of data collection. Similarly, hemodynamic changes due to morphological alterations after rupture have not been analyzed. The aim of this study was to investigate the changes in morphology and hemodynamics observed after aneurysm rupture. Methods: For 21 cerebral aneurysms (21 patients) that ruptured during observation, 3D geometry of the aneurysms and parent arteries were reconstructed based on the angiographic images before and after their rupture. In addition, using the reconstructed geometry, blood flow was simulated by computational fluid dynamics (CFD) analysis. Morphological and hemodynamic parameters were calculated both before and after rupture, and their changes from before to after were compared. Results: In the morphological parameters, statistically significantly higher values were observed after rupture in height (before: 5.5 ± 2.1 mm, after: 6.1 ± 2.0 mm; p < 0.0001), aspect ratio (p = 0.002), aneurysm volume (p = 0.04), and undulation index (p = 0.005). In terms of hemodynamic changes, the mean normalized wall shear stress (NWSS) decreased significantly (before: 5.4 × 10-1 ± 2.9 × 10-1, after: 4.4 × 10-1 ± 2.8 × 10-1; p < 0.001) as well as the other NWSS parameters, including maximum and minimum NWSS, which were associated with stagnant flow due to the morphological changes after rupture. Conclusions: Aneurysm morphology was found to change after rupture into an elongated and irregular geometry, accompanied by an increase in aneurysm volume. These morphological changes were also associated with statistically significant hemodynamic alterations that produced low wall sheer stress by stagnant flow. The authors' results also provide the opportunity to explore and develop a risk evaluation method for aneurysm rupture based on prerupture morphology and hemodynamics by further exploration in this direction.

Clinical Scales in Aneurysm Rupture Prediction

Article

Aug 2023

The rate of incidentally discovered unruptured intracranial aneurysms has increased with the broad availability of neuroimaging. The determination of the risk of rupture of brain aneurysms is challenging. Several clinical scales for aneurysm rupture prediction have been developed. The most common scales are PHASES, ELAPSS, and UIATS. These scales are not routinely used in clinical practice due to inherent shortcomings. In this review, we analyze the risk factors used in generating these scales and the performance of these scales in clinical studies. We also discuss new potential biomarkers and tools to predict aneurysm rupture.

Usefulness of transmission electron microscopy analysis in capturing the immunological phenotype of the host Fatima M Makhlouf Mohamed*1 and Cordula M. Stover2 e-mail: fatima.mohamed@su.edu.ly Sirte University Scientific Journal(Applied Sciences) Vol.9(1) ,June 2019

Article

Full-text available

Aug 2023

Fatima Mohamed Makhlouf Mohamed

Abstract The liver carries the main pathogen load during infection and is important for the defence against Listeria monocytogenes, however, the organ specific mechanisms that lead to the observed phenotype during listeriosis are undefined. L. monocytogenes (EGD-e), is a Gram-positive bacterium, intracellular pathogen, which can cause severe infectious disease in human and animals. Complement factor P or properdin is part of a system of proteins important in the first line immune defence against infection which plays a role in strengthening the complement activation. It has the ability to identify and bind to certain bacterial surfaces and enhances activation of the alternative pathway of complement. Since the liver is the main organ in the clearance of L. monocytogenes and represents an important localization of listerial proliferation, the role of properdin in intracellular localisation of L. monocytogenes in liver was studied using Transmission electron microscopy (TEM) in order to determine important processes and defined clearing processes of L. monocytogenes in the livers. In brief, the increase in bacterial burden in liver from properdin-deficient mice at 28-29 hours after L. monocytogenes infection were shown by TEM. Keywords: Properdin, Properdin-deficient mouse, Liver, Listeria monocytogenes.

Sensitivity of Hostile Hemodynamics to Aneurysm Geometry via Unsupervised Shape Interpolation

Article

Aug 2023
COMPUT METH PROG BIO

Background and objective: Vessel geometry and hemodynamics are intrinsically linked, whereby geometry determines hemodynamics, and hemodynamics influence vascular remodeling. Both have been used for testing clinical outcomes, but geometry/morphology generally has less uncertainty than hemodynamics derived from medical image-based computational fluid dynamics (CFD). To provide clinical utility, CFD-based hemodynamic parameters must be robust to modeling errors and/or uncertainties, but must also provide useful information not more-easily extracted from shape alone. The objective of this study was to methodically assess the response of hemodynamic parameters to gradual changes in shape created using an unsupervised 3D shape interpolation method. Methods: We trained the neural network NeuroMorph on 3 patient-derived intracranial aneurysm surfaces (labelled A, B, C), and then generated 3 distinct morph sequences (A→B, B→C, C→A) each containing 10 interpolated surfaces. From high-fidelity CFD simulation of these, we calculated a variety of common reduced hemodynamic parameters, including many previously associated with aneurysm rupture, and analyzed their responses to changes in shape, and their correlations. Results: The interpolated surfaces demonstrate complex, gradual changes in branch angles, vessel diameters, and aneurysm morphology. CFD simulation showed gradual changes in aneurysm jetting characteristics and wall-shear stress (WSS) patterns, but demonstrated a range of responses from the reduced hemodynamic parameters. Spatially and temporally averaged parameters including time-averaged WSS, time-averaged velocity, and low-shear area (LSA) showed low variation across all morph sequences, while parameters of flow complexity such as oscillatory shear, spectral broadening, and spectral bandedness indices showed high variation between slightly-altered neighboring surfaces. Correlation analysis revealed a great deal of mutual information with easier-to-measure shape-based parameters. Conclusions: In the absence of large clinical datasets, unsupervised shape interpolation provides an ideal laboratory for exploring the delicate balance between robustness and sensitivity of nominal hemodynamic predictors of aneurysm rupture. Parameters like time-averaged WSS and LSA that are highly "robust" may, as a result, be effectively redundant to morphological predictors, whereas more sensitive parameters may be too uncertain for practical clinical use. Understanding these sensitivities may help identify parameters that are capable of providing added value to rupture risk assessment.

A framework for intracranial aneurysm detection and rupture analysis on DSA

Article

Aug 2023

Background: Intracranial aneurysm is a severe cerebrovascular disease that can result in subarachnoid hemorrhage (SAH), leading to high incidence and mortality rates. Computer-aided detection of aneurysms can assist doctors in enhancing diagnostic accuracy. The analysis of aneurysm imaging holds considerable predictive value for aneurysm rupture. This paper presents a method for the detection of aneurysms and analysis of ruptures using digital subtraction angiography (DSA). Methods: A total of 263 aneurysms were analyzed, with 125 being ruptured and 138 being unruptured. Firstly, a filter based on the eigenvalues of the Hessian matrix was proposed for aneurysm detection. The filter's detection parameters can be automatically obtained through Bayesian optimization. Aneurysms were detected based on their structure and the response of the filter. Secondly, considering the variations in blood flow and morphology among aneurysms in DSA, intensity, texture, and blood perfusion features were extracted from the ruptured aneurysms and unruptured aneurysms. Subsequently, a sparse representation (SR) method was utilized to classify unruptured and ruptured aneurysms. Results: The experimental results for aneurysm detection showed that the F1-score was 94.1%. In the classification of ruptured and unruptured aneurysms, the accuracy, sensitivity, specificity, and area under curve (AUC) were 96.1%, 94.4%, 97.5%, and 0.982, respectively. Conclusion: This paper presents a scheme combining an aneurysm detection filter and machine learning, offering a reliable solution for the diagnosis and prediction of aneurysm rupture.

Risk Factors for Intracranial Aneurysm Rupture: A Clinical Case Series and Systematic Review of the Literature

Article

Full-text available

Jul 2023

Aim: To evaluate the patients who underwent surgery for an anterior communicating artery (AcomA) aneurysm at our institution. We analyzed our case series and systematically reviewed the literature to identify factors that could predict the rupture of an intracranial aneurysm in patients with AcomA aneurysms or any intracranial aneurysm. Material and Methods: We conducted a cross-sectional analysis of prospectively collected data from patients who underwent surgery for AcomA aneurysms at a single institution between January 2014 and May 2023. Predictors for the rupture of intracranial aneurysm were systematically reviewed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and the Pubmed and MEDLINE databases. Results: Younger age (odds ratio (OR): 0.957, 95% confidence interval (CI): 0.920–0.995, p = 0.028), presence of a daughter sac (OR: 3.209, 95% CI: 1.095–9.408, p = 0.034), and ever-smoking (OR: 0.357, 95% CI: 0.137–0.930, p = 0.035) were significant predictors of increased risk of rupture in patients with AcomA aneurysms. Several aneurysm- and patient-related risk factors for rupture of intracranial aneurysms were retrieved via the literature analysis. Conclusion: Younger age, ever-smoking, and presence of a daughter sac increased the risk of AcomA aneurysm rupture. A systematic literature review revealed several more aneurysm- and patient-related risk factors for rupture of the intracranial aneurysms. Our results could aid neurosurgeons during their decision-making process when treating patients with unruptured intracranial aneurysms.

Topological Data Analysis and Use of Mapper for Cerebral Aneurysm Rupture Status Discrimination Based on 3-Dimensional Shape Analysis

Article

Jun 2023
NEUROSURGERY

Background and objectives: Topological data analysis (TDA), which identifies patterns in data through simplified topological signatures, has yet to be applied to aneurysm research. We investigate TDA Mapper graphs (Mapper) for aneurysm rupture discrimination. Methods: Two hundred sixteen bifurcation aneurysms (90 ruptured) from 3-dimensional rotational angiography were segmented from vasculature and evaluated for 12 size/shape and 18 enhanced radiomics features. Using Mapper, uniformly dense aneurysm models were represented as graph structures and described by graph shape metrics. Mapper dissimilarity scores (MDS) were computed between pairs of aneurysms based on shape metrics. Lower MDS described similar shapes, whereas high MDS represented shapes that do not share common characteristics. Ruptured/unruptured average MDS scores (how "far" an aneurysm is shape-wise to ruptured/unruptured data sets, respectively) were evaluated for each aneurysm. Rupture status discrimination univariate and multivariate statistics were reported for all features. Results: The average MDS for pairs of ruptured aneurysms were significantly larger compared with unruptured pairs (0.055 ± 0.027 vs 0.039 ± 0.015, P < .0001). Low MDS suggest that, in contrast to ruptured aneurysms, unruptured aneurysms have similar shape characteristics. An MDS threshold value of 0.0417 (area under the curve [AUC] = 0.73, 80% specificity, 60% sensitivity) was identified for rupture status classification. Under this predictive model, MDS scores <0.0417 would identify unruptured status. MDS statistical performance in discriminating rupture status was similar to that of nonsphericity and radiomics Flatness (AUC = 0.73), outperforming other features. Ruptured aneurysms were more elongated (P < .0001), flatter (P < .0001), and showed higher nonsphericity (P < .0001) compared with unruptured. Including MDS in multivariate analysis resulted in AUC = 0.82, outperforming multivariate analysis on size/shape (AUC = 0.76) and enhanced radiomics (AUC = 0.78) alone. Conclusion: A novel application of Mapper TDA was proposed for aneurysm evaluation, with promising results for rupture status classification. Multivariate analysis incorporating Mapper resulted in high accuracy, which is particularly important given that bifurcation aneurysms are challenging to classify morphologically. This proof-of-concept study warrants future investigation into optimizing Mapper functionality for aneurysm research.

Evaluating a 3D deep learning pipeline for cerebral vessel and intracranial aneurysm segmentation from computed tomography angiography–digital subtraction angiography image pairs

Article

Full-text available

Jun 2023
Neurosurg Focus

OBJECTIVE Computed tomography angiography (CTA) is the most widely used imaging modality for intracranial aneurysm (IA) management, yet it remains inferior to digital subtraction angiography (DSA) for IA detection, particularly of small IAs in the cavernous carotid region. The authors evaluated a deep learning pipeline for segmentation of vessels and IAs from CTA using coregistered, segmented DSA images as ground truth. METHODS Using 50 paired CTA-DSA images, the authors trained (n = 27), validated (n = 3), and tested (n = 20) a deep learning model (3D DeepMedic) for cerebrovasculature segmentation from CTA. A landmark-based coregistration algorithm was used for registration and upsampling of CTA images to paired DSA images. Segmented vessels from the DSA were used as the ground truth. Accuracy of the model for vessel segmentation was evaluated using conventional metrics (dice similarity coefficient [DSC]) and vessel segmentation–specific metrics, like connectivity-area-length (CAL). On the test cases (20 IAs), 3 expert raters attempted to detect and segment IAs. For each rater, the authors recorded the rate of IA detection, and for detected IAs, raters segmented and calculated important IA morphology parameters to quantify the differences in IA segmentation by raters to segmentations by DeepMedic. The agreement between raters, DeepMedic, and ground truth was assessed using Krippendorf’s alpha. RESULTS In testing, the DeepMedic model yielded a CAL of 0.971 ± 0.007 and a DSC of 0.868 ± 0.008. The model prediction delineated all IAs and resulted in average error rates of < 10% for all IA morphometrics. Conversely, average IA detection accuracy by the raters was 0.653 (undetected IAs were present to a significantly greater degree on the ICA, likely due to those in the cavernous region, and were significantly smaller). Error rates for IA morphometrics in rater-segmented cases were significantly higher than in DeepMedic-segmented cases, particularly for neck (p = 0.003) and surface area (p = 0.04). For IA morphology, agreement between the raters was acceptable for most metrics, except for the undulation index (α = 0.36) and the nonsphericity index (α = 0.69). Agreement between DeepMedic and ground truth was consistently higher compared with that between expert raters and ground truth. CONCLUSIONS This CTA segmentation network (DeepMedic trained on DSA-segmented vessels) provides a high-fidelity solution for CTA vessel segmentation, particularly for vessels and IAs in the carotid cavernous region.

Biological and physical mechanisms of cerebral aneurysms formation, growth and rupture

Article

Full-text available

May 2023

According to various researchers, the prevalence of unruptured cerebral aneurysms (CAs) in the general population varies from 2 to 5 %. In the vast majority of cases, CAs do not have clinical and neurological manifestations and are discovered incidentally during routine neuroimaging studies. CAs can cause intracranial hemorrhage. As a rule, hemorrhages of this type occur in patients aged 40–60 years. It has been established that about 10–15 % of patients die from an aneurysmal hemorrhage before they receive specialized medical care. Recurrent aneurysmal intracranial hemorrhage is the main cause of high mortality and disability in this group of patients. The search for literature sources in the scientific databases PubMed/Medline, EMBASE, Cochrane Library and eLibrary demonstrated the existence of numerous studies devoted to the study of molecular biology and biophysical mechanisms of formation, growth and rupture of CAs. Combining the results of these studies was the motivation for writing this literature review. The paper reflects in detail the role of inflammation and molecular genetic factors in the growth and rupture of the CAs, and presents the biophysical factors of the rupture of the CAs. The authors pay special attention to the shape, size and coefficient of the CAs as the most important geometric risk factors for the formation and rupture of the CAs. This review presents current data on mathematical modeling of various types of CAs with an assessment of the risk of rupture of the latter, which has found its application in wide clinical practice. The authors also attempted to describe the hemodynamic features in various types of CAs. In turn, the type of blood flow in the CAs cavity largely depends on the size and shape of the latter and the geometry of the carrier artery, which is the basis for preoperative planning and the choice of tactics for surgical treatment of patients with unruptured CAs.

Imaging of Intracranial Saccular Aneurysms

Article

Mar 2023

Vascular imaging is an essential tool to appropriately diagnose and treat intracranial saccular aneurysms. There is extensive heterogeneity in aneurysm characteristics including location, size, shape, patient demographics, and clinical status that leads to a great diversity in both surgical and endovascular treatment options. This variability may elicit confusion when deciding the most appropriate imaging paradigm for an individual patient at particular time points. A collection of pre‐ and posttreatment scales and grades exist, but there is no current consensus on which one to implement. In this review, we discuss the key advantages and disadvantages of the available imaging modalities and how each can guide management. We also review novel imaging tools that are likely to alter the diagnostic landscape of intracranial aneurysms in the coming years.

Complex Morphologic Analysis of Cerebral Aneurysms Through the Novel Use of Fractal Dimension as a Predictor of Rupture Status

Article

Mar 2023

Background: Aneurysm morphology has been correlated with rupture. Previous reports identified several morphologic indices that predict rupture status, but they only measure specific qualities of an aneurysm's morphology in a semi-quantitative fashion. Fractal analysis is a geometric technique whereby a shape's overall complexity is quantified through the calculation of a fractal dimension (FD). By progressively altering a shape's scale of measurement and determining the number of segments required to incorporate the entire shape, a non-integer value for the shape's "dimension" is derived. We present a proof-of-concept study to calculate an aneurysm's FD for a small cohort of patients with aneurysms in two specific locations to determine whether FD is associated with aneurysm rupture status. Methods: Twenty-nine aneurysms of the posterior communicating and middle cerebral arteries were segmented from CT angiograms in 29 patients. FD was calculated using a standard box-counting algorithm extended for use with three-dimensional shapes. Non-sphericity index (NSI) and undulation index (UI) were used to validate the data against previously published parameters associated with rupture status. Results: Nineteen ruptured and ten unruptured aneurysms were analyzed. Through logistic regression analysis, lower FD was found to be significantly associated with rupture status (P = .035, OR = 0.64 95% CI [0.42-0.97] per FD increment of 0.05). Conclusion: In this proof-of-concept study, we present a novel approach to quantify the geometric complexity of intracranial aneurysms through FD. These data suggest an association between FD and patient-specific aneurysm rupture status.

Hemodynamic Shear Stress and Its Role in Atherosclerosis

Article

Full-text available

Dec 1999

Adel M Malek

Atherosclerosis, the leading cause of death in the developed world and nearly the leading cause in the developing world, is associated with systemic risk factors including hypertension, smoking, hyperlipidemia, and diabetes mellitus, among others. Nonetheless, atherosclerosis remains a geometrically focal disease, preferentially affecting the outer edges of vessel bifurcations. In these predisposed areas, hemodynamic shear stress, the frictional force acting on the endothelial cell surface as a result of blood flow, is weaker than in protected regions. Studies have identified hemodynamic shear stress as an important determinant of endothelial function and phenotype. Arterial-level shear stress (>15 dyne/cm2) induces endothelial quiescence and an atheroprotective gene expression profile, while low shear stress (<4 dyne/cm2), which is prevalent at atherosclerosis-prone sites, stimulates an atherogenic phenotype. The functional regulation of the endothelium by local hemodynamic shear stress provides a model for understanding the focal propensity of atherosclerosis in the setting of systemic factors and may help guide future therapeutic strategies.

Hemodynamic shear stress and its role in atherosclerosis

Article

Full-text available

Jan 2000

The folding of the human brain: From shape to function

Article

A. D Smith

Difference in configuration of ruptured and unruptured intracranial aneurysms determined by biplanar digital subtraction angiography

Article

Oct 2003

¶Summary There is an ongoing discussion about the risk of bleeding from unruptured intracranial aneurysms. Management guidelines were developed recently and some of the recommendations for decision making are based on the anatomical configuration of the aneurysm. The common assumption is that the presence of multiple lobes or a daughter sac indicates a higher risk of rupture. We have investigated the anatomical configuration of ruptured and unruptured intracranial aneurysms using biplanar digital subtraction angiography (DSA). The objective was to determine, whether there was a difference between ruptured and unruptured aneurysms regarding lobulation, the presence of a daughter sac or the shape as measured by the height/neck ratio. Biplanar DSA images of 124 patients were retrospectively analyzed. A total of 53 unruptured and 94 ruptured aneurysms were found (=147 aneurysms in total). Aneurysms of less than 10 mm diameter accounted for 82% of all aneurysms. Overall, 10% of unruptured aneurysm showed a multilobular appearance on DSA compared with 20% of ruptured aneurysms (Fisher’s exact test, p=0.10). In the 5–9 mm aneurysm group, multiple lobes were found significantly more frequent in ruptured aneurysms (26% vs. 4%, Fisher’s exact test, p<0.05). A height/neck ratio of less than 1.5 was not found in unruptured aneurysms (0/26) but in 21% (12/57) of ruptured aneurysms (p<0.05). Our data provide scientific support for using morphological features for the decision making process in the management of unruptured intracranial aneurysms. An irregular multilobar appearance was significantly more common in aneurysms of 5–9 mm size that ruptured.

Curvature Approximation for Triangulated Surfaces

Conference Paper

Jan 1992
COMPUTING

Bernd Hamann

Given a set of points and normals on a surface and a triangulation associated with them a simple scheme for approximating the principal curvatures at these points is developed. The approximation is based on the fact that a surface can locally be represented as the graph of a bivariate function. Quadratic polynomials are used for this local approximation. The principal curvatures at a point on the graph of such a quadratic polynomial is used as the approximation of the principal curvatures at an original surface point.

Growing Intracranial Aneurysms 1

Article

Oct 1976

Cerebral angiography is the best means by which an intracranial aneurysm can be demonstrated and studied in vivo. In 16 cases clinical deterioration paralleled a variable degree of enlargement of the aneurysms. In all patients the aneurysms were irregular and/or bior multilocular. Possible factors causing aneurysmal enlargement are discussed.

Three-dimensional computerized tomography angiography in the diagnosis of cerebrovascular disease

Article

Apr 1992
J NEUROSURG

Computer-generated three-dimensional reconstruction of the intracranial vascular system obtained by contrast-enhanced computerized tomography (CT) has been used in the diagnosis of 20 patients with known or suspected intracranial cerebrovascular disease. This technique allows visualization of the intracranial vasculature without exposing patients to the risks associated with intra-arterial angiography. The color prints and videotape images generated have been used to diagnose the presence of intracranial aneurysms, arteriovenous malformations, and venous angiomas. They have also been used to rule out structural abnormalities in patients with suspected intracranial vascular pathology and to screen patients with a strong family history of intracranial aneurysm. In 11 patients who underwent both three-dimensional CT angiography and intra-arterial angiography, the diagnostic correlation was 100%. No complications from the procedures or from incorrect diagnosis have been encountered. Although this technique requires further development and clinical evaluation, the authors' early experience with three-dimensional CT angiography suggests that this may become a valuable tool in the diagnosis of patients with cerebrovascular disease.

[Clinical study of growing up aneurysms: report of 25 cases]

Article

Oct 1991
NEUROL SURG TOKYO

Twenty-five cases of patients with growing up aneurysms are reported. Growth of the aneurysm was confirmed by repeated angiography within 1 month in 11 cases (short-term group), and for over 1 month in the other 14 cases (long-term group) following the initial angiography. Clinical history, shape and growth pattern of aneurysms, as well as hemodynamic factors that effect the growth were investigated in each group. The aneurysms were classified according to the shape into dome-type (smooth contour) and bleb-type (irregular contour). In all cases of the short-term group, the first angiography was performed because of rupture of the aneurysm. In this group, 4 cases bled again because of enlargement or the development of an aneurysmal bleb. Growth rate and the initial size of the aneurysm did not effect the potential of re-rupture. In the long-term group, 9 cases out of 14 (64.3%) had "non-ruptured aneurysm" at the time of first angiography. In the follow up, 5 cases were ruptured (two because of re-bleeding and three for the first time). In 3 out of these 5 cases, a bleb was demonstrated on initial angiography, and in another case, a bleb was demonstrated in follow-up angiography. Only one case ruptured because of the growth of the aneurysmal dome. Most of the aneurysms that rupture, in the follow-up survey, showed a larger growth rate in comparison with aneurysms that did not rupture. Many cases of this long-term group were associated with hypertension or vascular abnormalities which would effect the aneurysmal growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinico-statistical study on morphological risk factors of middle cerebral artery aneurysms

Article

Feb 1990

Influences of various factors on postoperative outcome of 122 well-documented cases, out of a total of 151 cases of middle cerebral artery aneurysm, are discussed in this paper. The shape of the aneurysm, major axis, major axis/neck and major/minor axis ratio were correlated with the presence or absence of a bleb (p less than 0.0000001), and indicated a correlation not only between aneurysmal shape and the outcome (p less than 0.05) but also between preoperative seriousness and the outcome (p less than 0.05). The preoperative seriousness and the grade of subarachnoid haemorrhage indicated a close correlation between each of these two parameters and the outcome (p less than 0.000001 for each). Both the quantity and the colour of CSF outflow from the chiasmal cistern showed close correlation with vasospasm (p less than 0.01), onset of hydrocephalus (p less than 0.01) and the outcome (p less than 0.001). Moreover, vasospasm and hydrocephalus grade itself also showed close correlation with the outcome (p less than 0.001 and p less than 0.00001). All parameters: blood pressure grade, BPmax, BPmin, BP fluctuation showed correlations not only with preoperative seriousness (p less than 0.001) and the outcome (p less than 0.0001) but also with subarachnoid haemorrhage frequency, number of aneurysms, and major axis/neck ratio.

Hemodynamics and atherosclerosis. Insights and perspectives gained from studies of human arteries

Article

Nov 1988

Atherosclerosis affects the major elastic and muscular arteries, but some vessels are largely spared while others may be markedly diseased. The carotid bifurcation, the coronary arteries, the infrarenal abdominal aorta, and the vessels supplying the lower extremities are at highest risk. The propensity for plaque formation at bifurcations, branchings, and curvatures has led to conjectures that local mechanical factors such as wall shear stress and mural tensile stress potentiate atherogenesis. Recent studies of the human vessels at high risk, and of corresponding models, have provided quantitative evidence that plaques tend to occur where flow velocity and shear stress are reduced and flow departs from a laminar, unidirectional pattern. Such flow characteristics tend to increase the residence time of circulating particles in susceptible regions while particles are cleared rapidly from regions of relatively high wall shear stress and laminar unidirectional flow. The flow patterns associated with plaque localization are most prominent during systole. Long-term consequences are therefore likely to be greatly enhanced by elevated heart rate and may exert a selective effect on the coronary arteries. The point-by-point redistribution of wall tension at regions of geometric transition has not been quantitatively related to plaque localization. Enlargement of arteries as plaques increase in size and the associated modeling of plaque and wall configuration tend to preserve an adequate and regular lumen cross section. Hemodynamic forces appear to determine changes in vessel diameter so as to restore normal levels of wall shear stress, while wall thickness architecture, and composition are closely related to tensile stress. Hemodynamic forces may also be implicated in the symptom-producing destabilization of plaques, especially in relation to wall instabilities near stenoses. The relative roles of wall shear stress, tensile stress, and the metabolism of the artery wall in the progression and complication of atherosclerosis remain to be clarified. Development of clinical techniques for relating hemodynamic and tensile properties to plaque location, stenosis, and composition should permit pathologists to provide new insights into the bases for the topographic and individual differences in plaque progression and outcome.

Mechanism of Growth and Rupture in Cerebral Berry Aneurysms

Article

Jun 1966

M R Crompton

A nonlinear mathematical model for the development and rupture of intracranial fusiform aneurysms

Article

Jan 1995

Laplace's law, which describes a linear relation between the tension and the radius, is often used to characterize the mechanical response of the aneurysm wall to distending pressures. However, histopathological studies have confirmed that the wall of the fully developed aneurysm consists primarily of collagen and is subject to large increases in tension for small increases in the radius, i.e., a nonlinear relationship exists between the tension within the aneurysm wall and the radius. Thus, a nonlinear version of Laplace's law is proposed to accurately describe the development and rupture of a fusiform saccular aneurysm. The fusiform aneurysm was modelled as a thin-walled ellipsoidal shell with a major axis radius, Ra, minor axis radius, Rb, circumferential tension, S0, and meridional tension, S phi, with phi defining the angle from the surface normal. Using both linear and nonlinear models, differential expressions of the volume distensibility evaluated at 90 degrees were used to determine the critical radius of the aneurysm along the minor axis from S0 and S phi in terms of the following geometric and biophysical variables; A, elastic modulus of collagen; E, elastic modulus of the aneurysm (elastin and collagen); t, wall thickness; P, systolic pressure; and Ra. For typical physiological values of A = 2.8 MPa, E = 1.0 MPa, T = 40 microns, P = 150 mmHg, and Ra = 4Rb, the linear model yielded critical radii of 4.0 mm from S phi and 2.2 mm from S0. The resultant critical radius was 4.56 mm. Using the same values, the critical radii from the tension components of the nonlinear model were 3.5 mm from S phi and 1.9 mm from S0.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth and rupture of unruptured cerebral aneurysms based on the intraoperative appearance

Article

Nov 1994
ACTA MED OKAYAMA

The growth and rupture of 40 cerebral aneurysms was studied in 36 patients (14 men, 22 women; were average age, 51.8 years). Aneurysms were classified into five types according to the intraoperative findings: type 1, uniformly thin, smooth surface; type 2, thin neck and thick wall, smooth surface with or without red and/or transparent portions; type 3, uniformly thick wall, smooth surface with or without red portions; type 4, thick neck, bubbled or loculated thin wall at dome with or without red and/or transparent portions; type 5, thick wall in entirety, irregular surface with or without red portions. Five were type 1, six type 2, and 12 type 3. In four of the type 2 aneurysms, turbulence could be seen at the neck. In seven of the type 3 aneurysms, red and/or transparent portions were observed in the wall. Thirteen were type 4; nine of which had a bubbled or loculated wall with or without red and/or transparent portions. Four were type 5, with scattered red portions but a thick wall. Type 1 aneurysms were 2-5 mm, most of types 2 and 3 were 3-6 mm, type 4 were 3-13 mm, and type 5 were more than 9 mm. Types 1 and 2 had few local changes in the wall, suggesting that aneurysms at this stage are stable. Type 3 is considered to be a transitional stage to type 4 from type 2. Type 4 aneurysms had some local changes within the wall including bubbles or loculi. We concluded that aneurysms exceeding 4 mm have local pathologic changes in the wall and are critical.(ABSTRACT TRUNCATED AT 250 WORDS)

A nonlinear mathematical model for the development and rupture of intracranial saccular aneurysms

Article

Nov 1994

Mathematical models of aneurysms are typically based on Laplace's law which defines a linear relation between the circumferential tension and the radius. However, since the aneurysm wall is viscoelastic, a nonlinear model was developed to characterize the development and rupture of intracranial spherical aneurysms within an arterial bifurcation and describes the aneurysm in terms of biophysical and geometric variables at static equilibrium. A comparison is made between mathematical models of a spherical aneurysm based on linear and nonlinear forms of Laplace's law. The first form is the standard Laplace's law which states that a linear relation exists between the circumferential tension, T, and the radius, R, of the aneurysm given by T = PR/2t where P is the systolic pressure. The second is a 'modified' Laplace's law which describes a nonlinear power relation between the tension and the radius defined by T = ARP/2At where A is the elastic modulus for collagen and t is the wall thickness. Differential expressions of these two relations were used to describe the critical radius or the radius prior to aneurysm rupture. Using the standard Laplace's law, the critical radius was derived to be Rc = 2Et/P where E is the elastic modulus of the aneurysm. The critical radius from the modified Laplace's law was R = [2Et/P]2At/P. Substituting typical values of E = 1.0 MPa, t = 40 microns, P = 150 mmHg, and A = 2.8 MPa, the critical radius is 4.0 mm using the standard Laplace's law and 4.8 mm for the modified Laplace's law.(ABSTRACT TRUNCATED AT 250 WORDS)

Natural history and risk factors of unruptured cerebral aneurysms

Article

Oct 1993
CLIN NEUROL NEUROSUR

We report the results of a statistical analysis of the long-term outcome of 54 patients with 72 unruptured cerebral aneurysms, and identify the factors for predicting subsequent ruptures. Twenty-two patients died during the observation period, which averaged 43.7 months. The 5-year survival rate was 56%. Aneurysms ruptured in 11 patients (20.4%), 10 of whom died without undergoing surgery. The annual bleeding rate was 1.92%. The average size of the 11 ruptured aneurysms was 13.1 mm. In 4 patients, however, bleeding occurred in unruptured cerebral aneurysms of 4 and 5 mm, which suggests that leaving unruptured cerebral aneurysms of less than 10 mm in size untreated is hazardous. According to the Cox proportional hazards model, the shape and location of the aneurysm and the presence of hypertension were the most important factors for predicting a subsequent rupture. Our data suggest that unruptured cerebral aneurysms arising from the vertebrobasilar and middle cerebral arteries of 10-19 mm size and of multilobes had a statistically high probability of subsequent bleeding. Although 20 patients with 28 unruptured cerebral aneurysms were followed through repeated examinations, we could not correlate the risk of subsequent bleeding with changes in the size of the aneurysm.

A new index of abdominal adiposity as an indicator of risk for cardiovascular disease. A cross-population study

Article

Mar 1993

A new index of abdominal adiposity, the conicity index, and the waist-to-hip ratio (WHR) were compared as health indicators in seven European populations and two USA populations. The total sample included 1280 men and 960 women. Abdominal adiposity as detected by these indices is significantly associated with more cardiovascular risk indicators among women than it is among men. Both indices are equivalent as health indicators. However, the conicity index has several advantages over the WHR: (i) it has a theoretical (expected) range; (ii) it includes a built-in adjustment of waist circumference for height and weight, allowing direct comparisons of abdominal adiposity between individuals or even between populations; and (iii) it does not require the hip circumference to assess fat distribution.

Influence of size, shape and properties on the mechanics of axisymmetric saccular aneurysms

Article

Sep 1996
J BIOMECH

Rupture of intracranial saccular aneurysms is the most common cause of spontaneous subarachnoid hemorrhage which, despite advances in neurosurgery, continues to result in significant morbidity and mortality. Currently, the decision to treat a diagnosed, unruptured aneurysm is based primarily on the maximum dimension of the lesion even though there is controversy over the 'critical size' (e.g. many 'large' lesions do not rupture whereas some 'small' ones do). There is a need, therefore, for improved predictors of the rupture-potential of these lesions. In this paper, we show that it is highly unlikely that saccular aneurysms expand or rupture due to a limit point instability, and suggest that a rupture-criterion should be based on local multiaxial states of stress or strain. Moreover, our results from nonlinear finite element analyses reveal important roles of lesion shape, material properties, and loading conditions, not just size, in governing the distributions of stress and strain within a sub-class of axisymmetric saccular aneurysms. For example, we find that maximum biaxial stresses and strains are most often at the fundus, where rupture tends to occur, and that maximum stresses increase markedly with increases in lesion size, the ratio of neck diameter to lesion height, and the distending transmural pressure.

The Influence of Shape on the Stresses in Model Abdominal Aortic Aneurysms

Article

Sep 1996

Presence of a small abdominal aortic aneurysm (AAA) often presents a difficult clinical dilemma--a reparative operation with its inherent risks versus monitoring the growth of the aneurysm, with the accompanying risk of rupture. The risk of rupture is conventionally believed to be a function of the AAA bulge diameter. In this work, we hypothesized that the risk of rupture depends on AAA shape. Because rupture is inevitably linked to stress, membrane theory was used to predict the stresses in the walls of an idealized AAA, using a model which was axisymmetric and fusiform, with the ends merged into straight opened-ended tubes. When the stresses for many different shapes of model AAAs were examined, a number of conclusions became evident: (i) maximum hoop stress typically exceeded maximum meridional stress by a factor of 2 to 3 (ii) the shape of an AAA had a small effect on the meridional stresses and a rather dramatic effect on the hoop stresses, (iii) maximum stress typically occurred near the inflection point of a curve drawn coincident with the AAA wall, and (iv) the maximum stress was a function--not of the bulge diameter---but of the curvatures (i.e. shape) of the AAA wall. This last result suggested that rupture probability should be based on wall curvatures, not on AAA bulge diameter. Because curvatures are not much harder to measure than bulge diameter, this concept may be useful in a clinical setting in order to improve prediction of the likelihood of AAA rupture.

A nonlinear quasi-static model of intracranial aneurysms

Article

Nov 1997

Biomathematical models of intracranial aneurysms can provide qualitative and quantitative information on stages of aneurysm development through elucidation of biophysical interactions and phenomena. However, most current aneurysm models, based on Laplace's law, are renditions of static, linearly elastic spheres. The primary goal of this study is to: 1. develop a nonlinear constitutive quasi-static model and 2. derive an expression for the critical size/pressure of an aneurysm, with subsequent applications to clinical data. A constitutive model of an aneurysm, based on experimental data of tissue specimens available in the literature, was incorporated into a time-dependent set of equations describing the dynamic behavior of a saccular aneurysm in response to pulsatile blood flow. The set of differential equations was solved numerically, yielding mathematical expressions for aneurysm radius and pressure. This model was applied to clinical data obtained from 24 patients presenting with ruptured aneurysms. Aneurysm development and eventual rupture exhibited an inverse relationship between aneurysm size and blood pressure. In general, the model revealed that rupture becomes highly probable for an aneurysm diameter greater than 2.0 mm and a systemic blood pressure greater than 125 mmHg. However, an interesting observation was that the critical pressure demonstrated a minimal sensitivity to the critical radius, substantiating similar clinical and experimental observations that blood pressure was not correlated, to any degree, with aneurysm rupture. Undulations in the aneurysm wall, presented by irregular multilobulated morphologies, could play an important role in aneurysm rupture. However, due to the large variation in results, more extensive studies will be necessary for further evaluation and validation of this model.

Mechanical wall stress in abdominal aortic aneurysm: Influence of diameter and asymmetry

Article

May 1998
J VASC SURG

Risk for rupture of an abdominal aortic aneurysm is widely believed to be related to its maximum diameter. From a biomechanical standpoint, however, risk is probably more precisely related to mechanical wall stress. Many abdominal aortic aneurysms are asymmetric (for example because of anterior bulging with posterior expansion limited by the vertebral column). The purpose of this work was to investigate the effect of maximum diameter and asymmetric bulge on wall stress. Three-dimensional computer models of abdominal aortic aneurysms were generated. In one protocol, maximum diameter was held constant while bulge shape factor was varied. The shape factor took into account the asymmetric shape of the bulge. In a second protocol, the shape of the aneurysmal wall was held constant while maximum diameter was varied. Wall stress was computed in each instance with a commercial software package and assumption of physiologic intraluminal pressure. Both maximum diameter and the shape factor were found to have substantial influence on the distribution of wall stress within the aneurysm. In some instances the maximum stress occurred at the midsection, and in others it occurred elsewhere. The magnitude of peak stress acting on the aneurysm increased nonlinearly with increasing maximum diameter or increasing asymmetry. Our computer models showed that the stress within the wall of an abdominal aortic aneurysm and possibly the potential for rupture are as dependent on aneurysm shape as they are on maximum diameter. This information may be important in determining severity of individual abdominal aortic aneurysms and in improving understanding of the natural history of the disease.

Anatomical and morphological factors correlating with rupture of intracranial aneurysms in patients referred for endovascular treatment

Article

Dec 1998

The size of intracranial aneurysms is the only characteristic shown to correlate with their rupture. However, the critical size for rupture has varied considerably among previous accounts and remains a point of controversy. Our goal was to identify statistically significant clinical and morphological factors predictive of the occurrence of rupture and aneurysm size in patients referred for endovascular treatment. We retrospectively recorded the following factors from 74 patients who presented with ruptured (40) or unruptured (34) aneurysms: aneurysm morphology (uni/multilobulated), location (anterior/posterior), maximum diameter, diameter of the neck, and the patient's age and sex. We performed stepwise discriminant, and stepwise and logistic regression analysis to identify factors predicting rupture and the size of the aneurysm at rupture. The mean diameter of the ruptured aneurysms was 11.9+/-6.3 mm, range 3.0-33.0 mm, and that of the unruptured aneurysm 13.5+/-5.8 mm, range 5.0-30 mm. Stepwise discriminant analysis identified aneurysm morphology (P < 0.001) and location in the intracranial circulation (P < 0.001) as statistically significant factors in predicting rupture. Stepwise regression analysis revealed that aneurysm morphology and the size of the neck were predictors of aneurysm size at rupture.

Effects of Size and Shape (Aspect Ratio) on the Hemodynamics of Saccular Aneurysms: A Possible Index for Surgical Treatment of Intracranial Aneurysms

Article

Jul 1999

The present study was undertaken to explore the relationship between the characteristic geometry of aneurysms prone to rupture and the blood flow patterns therein, using microsurgically produced aneurysms that simulated human middle cerebral artery aneurysms in scale and shape. We measured in vivo velocity profiles using our 20-MHz, 80-channel, Doppler ultrasound velocimeter. We produced small (< or =5 mm, 5 cases) and large (6-13 mm, 12 cases) aneurysms with round, dumbbell, or multilobular shapes. The fundamental patterns of intra-aneurysmal flow were composed of inflow, circulating flow, and outflow. The inflow, which entered the aneurysm only during the systolic phase, was strongly influenced by the position and size of the neck and the flow ratio into the distal branches. The outflow was usually nonpulsatile and of low velocity. The circulating flow depended on the aspect ratio (depth/neck width). A single recirculation zone was observed in aneurysms with aspect ratios of less than 1.6. This circulation did not seem to extend to areas with aspect ratios greater than this value; in aneurysms with aspect ratios of more than 1.6, a much slower circulation was observed near the dome. Furthermore, in the dome of dumbbell-shaped aneurysms and daughter aneurysms, no flow was detected. Intra-aneurysmal flow was determined by the aspect ratio, rather than the aneurysm size. The localized, extremely low-flow condition that was observed in the dome of aneurysms with aspect ratios of more than 1.6 is a common flow characteristic in the geometry of ruptured aneurysms, so great care should be taken for patients with unruptured intracranial aneurysms with aspect ratios of more than 1.6.

Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm

Article

May 2000
J VASC SURG

Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical stress acting on the wall exceeds the strength of the wall tissue. Therefore, knowledge of the stress distribution in an intact AAA wall could be useful in assessing its risk of rupture. We developed a methodology to noninvasively estimate the in vivo wall stress distribution for actual AAAs on a patient-to-patient basis. Six patients with AAAs and one control patient with a nonaneurysmal aorta were the study subjects. Data from spiral computed tomography scans were used as a means of three-dimensionally reconstructing the in situ geometry of the intact AAAs and the control aorta. We used a nonlinear biomechanical model developed specifically for AAA wall tissue. By means of the finite element method, the stress distribution on the aortic wall of all subjects under systolic blood pressure was determined and studied. In all the AAA cases, the wall stress was complexly distributed, with distinct regions of high and low stress. Peak wall stress among AAA patients varied from 29 N/cm(2) to 45 N/cm(2) and was found on the posterior surface in all cases studied. The wall stress on the nonaneurysmal aorta in the control subject was relatively low and uniformly distributed, with a peak wall stress of 12 N/cm(2). AAA volume, rather than AAA diameter, was shown by means of statistical analysis to be a better indicator of high wall stresses and possibly rupture. The approach taken to estimate AAA wall stress distribution is completely noninvasive and does not require any additional involvement or expense by the AAA patient. We believe that this methodology may allow for the evaluation of an individual AAA's rupture risk on a more biophysically sound basis than the widely used 5-cm AAA diameter criterion.

Is the Aspect Ratio a Reliable Index for Predicting the Rupture of a Saccular Aneurysm?

Article

Apr 2001

The present retrospective study was undertaken to prove the reliability of the aspect ratio (aneurysm depth to aneurysm neck width) for predicting an aneurysmal rupture. The aspect ratio is considered a better geometric index than aneurysm size for determining the intra-aneurysmal blood flow. We measured the aspect ratios and the sizes of aneurysms, as determined by examining angiographic films magnified 1.4x, in 129 patients with ruptured aneurysms and in 72 patients with 78 unruptured aneurysms. After categorizing the aneurysms into four groups on the basis of their locations (aneurysms of the anterior communicating artery, middle cerebral artery, internal carotid artery-posterior communicating artery [ICA-PComA], and other aneurysms), a statistical analysis of ruptured and unruptured aneurysms was performed. The mean aneurysm size was found to be statistically significant in the aneurysms at the ICA-PComA and in locations excluding the anterior communicating artery, the middle cerebral artery, and the ICA-PComA. However, the mean aspect ratio was statistically significant at all four locations. In patients with ruptured aneurysms, no ruptured aneurysms with an aspect ratio of less than 1.0 were found. The distribution of the ruptured group versus the unruptured group with an aspect ratio of less than 1.6 at each location was 13 versus 79%, respectively, at the anterior communicating artery, 11 versus 58% at the middle cerebral artery, 11% versus 85% at the ICA-PComA, and 7 versus 81% at other locations. The aspect ratio between ruptured aneurysms and unruptured aneurysms was found to be statistically significant, and almost 80% of the ruptured aneurysms showed an aspect ratio of more than 1.6, whereas almost 90% of the unruptured aneurysms showed an aspect ratio of less than 1.6. This study therefore suggests that the aspect ratio may be useful in predicting imminent aneurysmal ruptures.

Rheological characteristics of the aneurysm at the middle cerebral artery bifurcation

Article

Nov 2001
NEUROL SURG TOKYO

We performed a retrospective clinical study to estimate the morphological index such as aspect ratio (aneurysm depth/neck) and area ratio (ratio of the cross-sectional area of bifurcated arteries) of 64 cases with saccular aneurysms (ruptured aneurysms: 41, unruptured aneurysms: 23) at the bifurcation of the middle cerebral artery (MCA) and made a flow visualization study using a flat three dimensional acrylic aneurysm model to define the flow characteristics in conditions similar to those obtained from the clinical study. The mean aspect ratio and area ratio of the ruptured and unruptured aneurysm cases were 2.81 +/- 1.45, 2.52 +/- 0.91 and 1.56 +/- 0.59, 1.73 +/- 0.38. These respective values differ statistically. The area ratio of the MCA bifurcation with no aneurysm was 1.25 +/- 0.35. This value was also statistically different from the ruptured aneurysm case. The visualization study was performed changing the neck size and flow ratio into the peripheries to simulate various aspect ratio and flow ratio into peripheries. The results showed that intraanerysmal flow was definitely influenced by aspect ratio and area ratio. The aspect ratio over 2.0 and area ratio below 2.0 failed to drive the inflow inside the aneurysms and developed as a stagnant area in the dome side. The morphological index of aspect ratio and area ratio reflected the flow characteristics in the aneurysm and was statistically different in ruptured and unruptured aneurysm cases. The unruptured aneurysms with an aspect ratio of more than 1.6 and an area ratio of more than 2.0 must be followed up, because of the risk that they might rupture in the near future.

Unruptured intracranial aneurysms: A review

Article

Feb 2002
J NEUROSURG

Bryce Weir

In this article, pathological, radiological, and clinical information regarding unruptured intracranial aneurysms is reviewed. Treatment decisions require that surgeons and interventionists take into account information obtained in pathological, radiological, and clinical studies of unruptured aneurysms. The author has performed a detailed review of the literature and has compared, contrasted, and summarized his findings. Unruptured aneurysms may be classified as truly incidental, part of a multiple aneurysm constellation, or symptomatic by virtue of their mass, irritative, or embolic effects. Unruptured aneurysms with clinical pathological profiles resembling those of ruptured lesions should be considered for treatment at a smaller size than unruptured lesions with profiles typical of intact aneurysms, as has been determined at autopsy in patients who have died of other causes. The track record of the surgeon or interventionist and the institution in which treatment is to be performed should be considered while debating treatment options. In cases in which treatment is not performed immediately, ongoing periodic radiological assessment may be wise. Radiological investigations to detect unruptured aneurysms in asymptomatic patients should be restricted to high-prevalence groups such as adults with a strong family history of aneurysms or patients with autosomal dominant polycystic kidney disease. All patients with intact lesions should be strongly advised to discontinue cigarette smoking if they are addicted. The current state of knowledge about unruptured aneurysms does not support the use of the largest diameter of the lesion as the sole criterion on which to base treatment decisions, although it is of undoubted importance.

In vivo analysis of mechanical wall stress and abdominal aortic aneurysm rupture risk

Article

Oct 2002
J VASC SURG

The purpose of this study was to calculate abdominal aortic aneurysm (AAA) wall stresses in vivo for ruptured, symptomatic, and electively repaired AAAs with three-dimensional computer modeling techniques, computed tomographic scan data, and blood pressure and to compare wall stress with current clinical indices related to rupture risk. CT scans were analyzed for 48 patients with AAAs: 18 AAAs that ruptured (n = 10) or were urgently repaired for symptoms (n = 8) and 30 AAAs large enough to merit elective repair within 12 weeks of the CT scan. Three-dimensional computer models of AAAs were reconstructed from CT scan data. The stress distribution on the AAA as a result of geometry and blood pressure was computationally determined with finite element analysis with a hyperelastic nonlinear model that depicted the mechanical behavior of the AAA wall. Peak wall stress (maximal stress on the AAA surface) was significantly different between groups (ruptured, 47.7 +/- 6 N/cm(2); emergent symptomatic, 47.5 +/- 4 N/cm(2); elective repair, 36.9 +/- 2 N/cm(2); P =.03), with no significant difference in blood pressure (P =.2) or AAA diameter (P =.1). Because of trends toward differences in diameter, comparison was made only with diameter-matched subjects. Even with identical mean diameters, ruptured/symptomatic AAAs had a significantly higher peak wall stress (46.8 +/- 4.5 N/cm(2) versus 38.1 +/- 1.3 N/cm(2); P =.05). Maximal wall stress predicted risk of rupture better than the LaPlace equation (20.7 +/- 5.7 N/cm(2) versus 18.8 +/- 2.9 N/cm(2); P =.2) or other proposed indices of rupture risk. The smallest ruptured AAA was 4.8 cm, but this aneurysm had a stress equivalent to the average electively repaired 6.3-cm AAA. Peak wall stresses calculated in vivo for AAAs near the time of rupture were significantly higher than peak stresses for electively repaired AAAs, even when matched for maximal diameter. Calculation of wall stress with computer modeling of three-dimensional AAA geometry appears to assess rupture risk more accurately than AAA diameter or other previously proposed clinical indices. Stress analysis is practical and feasible and may become an important clinical tool for evaluation of AAA rupture risk.

Carotid body tumor: Three-dimensional imaging

Article

May 2003
J VASC SURG

Mark F. Fillinger

Prediction of rupture risk in abdominal aortic aneurysm during observation: Wall stress versus diameter * ** * **

Article

Apr 2003
J VASC SURG

We previously showed that peak abdominal aortic aneurysm (AAA) wall stress calculated for aneurysms in vivo is higher at rupture than at elective repair. The purpose of this study was to analyze rupture risk over time in patients under observation. Computed tomography (CT) scans were analyzed for patients with AAA when observation was planned for at least 6 months. AAA wall stress distribution was computationally determined in vivo with CT data, three-dimensional computer modeling, finite element analysis (nonlinear hyperelastic model depicting aneurysm wall behavior), and blood pressure during observation. Analysis included 103 patients and 159 CT scans (mean follow-up, 14 +/- 2 months per CT). Forty-two patients were observed with no intervention for at least 1 year (mean follow-up, 28 +/- 3 months). Elective repair was performed within 1 year in 39 patients, and emergent repair was performed in 22 patients (mean, 6 +/- 1 month after CT) for rupture (n = 14) or acute severe pain. Significant differences were found for initial diameter (observation, 4.9 +/-.1 cm; elective repair, 5.9 +/-.1 cm; emergent repair, 6.1 +/-.2 cm; P <.0001) and initial peak wall stress (38 +/- 1 N/cm(2), 42 +/- 2 n/cm(2), 58 +/- 4 N/cm(2), respectively; P <.0001), but peak wall stress appeared to better differentiate patients who later required emergent repair (elective vs emergent repair: diameter, 3% difference, P =.5; stress, 38% difference, P <.0001). Receiver operating characteristic (ROC) curves for predicting rupture were better for peak wall stress (sensitivity, 94%; specificity,81%; accuracy, 85% [with 44 N/cm(2) threshold]) than for diameter (81%, 70%, 73%, respectively [with optimal 5.5 cm threshold). With proportional hazards analysis, peak wall stress (relative risk, 25x) and gender (relative risk, 3x) were the only significant independent predictors of rupture. For AAAs under observation, peak AAA wall stress seems superior to diameter in differentiating patients who will experience catastrophic outcome. Elevated wall stress associated with rupture is not simply an acute event near the time of rupture.

Unruptured intracranial aneurysms: Natural history, clinical outcome, and risks of surgical and endovascular treatment

Article

Aug 2003
LANCET

The management of unruptured intracranial aneurysms is controversial. Investigators from the International Study of Unruptured Intracranial Aneurysms aimed to assess the natural history of unruptured intracranial aneurysms and to measure the risk associated with their repair. Centres in the USA, Canada, and Europe enrolled patients for prospective assessment of unruptured aneurysms. Investigators recorded the natural history in patients who did not have surgery, and assessed morbidity and mortality associated with repair of unruptured aneurysms by either open surgery or endovascular procedures. 4060 patients were assessed-1692 did not have aneurysmal repair, 1917 had open surgery, and 451 had endovascular procedures. 5-year cumulative rupture rates for patients who did not have a history of subarachnoid haemorrhage with aneurysms located in internal carotid artery, anterior communicating or anterior cerebral artery, or middle cerebral artery were 0%, 2. 6%, 14 5%, and 40% for aneurysms less than 7 mm, 7-12 mm, 13-24 mm, and 25 mm or greater, respectively, compared with rates of 2 5%, 14 5%, 18 4%, and 50%, respectively, for the same size categories involving posterior circulation and posterior communicating artery aneurysms. These rates were often equalled or exceeded by the risks associated with surgical or endovascular repair of comparable lesions. Patients' age was a strong predictor of surgical outcome, and the size and location of an aneurysm predict both surgical and endovascular outcomes. Many factors are involved in management of patients with unruptured intracranial aneurysms. Site, size, and group specific risks of the natural history should be compared with site, size, and age-specific risks of repair for each patient.

Three-Dimensional Geometrical Characterization of Cerebral Aneurysms

Article

Mar 2004

The risk of rupture of cerebral aneurysms has been correlated with the size of the aneurysm sac. It is conceivable that geometrical shape, not just size may also be related to aneurysm rupture potential. Further, aneurysm shape may also be a factor in deciding on treatment modalities, i.e., to clip or coil. However, our ability to make use of available information on aneurysm shape remains poor. In this study, methods were developed to quantify the seemingly arbitrary three-dimensional geometry of the aneurysm sac, using differential and computational geometry techniques. From computed tomography angiography (CTA) data, the three-dimensional geometry of five unruptured human cerebral aneurysms was reconstructed. Various indices (maximum diameter, neck diameter, height, aspect ratio, bottleneck factor, bulge location, volume, surface area, Gaussian and mean curvatures, isoperimetric ratio, and convexity ratio) were utilized to characterize the geometry of these aneurysm surfaces and four size-matched hypothetical control aneurysms. The physical meanings of various indices and their possible role as prognosticators for rupture risk and presurgical planning were discussed.

Accepted in final form September 23 This work was supported by the Cordis Basic Science Award in Neurovascular Disease Address reprint requests to: Penn State Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania 17003. email: rharbaugh@psu

48-362

Fm White
Viscous
Flow
E Robert
M D Harbaugh

White FM: Viscous Fluid Flow, ed 2. New York: McGraw-Hill, 1991 Manuscript received June 20, 2004. Accepted in final form September 23, 2004. This work was supported by the Cordis Basic Science Award in Neurovascular Disease, 2004. Address reprint requests to: Robert E. Harbaugh, M.D., Room 3830, Biomedical Research Building, Penn State Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania 17003. email: rharbaugh@psu.edu. M. L. Raghavan, B. Ma, and R. E. Harbaugh 362 J. Neurosurg. / Volume 102 / February, 2005 02_05_JNS.3 1/24/05 2:48 PM Page 362

/ Volume 102 / February, 2005 Quantified aneurysm shape and rupture risk 361 rMW: Wall stress distribution on three-dimensionally reconstruct-ed models of human abdominal aortic aneurysm

760-769

Ml Raghavan
Da Vorp
Mp Federle
Ms Makaroun
J Webster
Neurosurg

Raghavan ML, Vorp DA, Federle MP, Makaroun MS, Webster J. Neurosurg. / Volume 102 / February, 2005 Quantified aneurysm shape and rupture risk 361 rMW: Wall stress distribution on three-dimensionally reconstruct-ed models of human abdominal aortic aneurysm. J Vasc Surg 31: 760–769, 200

Quantified aneurysm shape and rupture risk MW: Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm

Jan 2000
760-769

Quantified aneurysm shape and rupture risk MW: Wall stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm. J Vasc Surg 31: 760–769, 2000

Evaluation of the aspect ratio of cerebral aneurysms as a predictor of rupture American Association of Neurological Surgeons

Jan 2000

Vs Purighalla
Ml Raghavan
Re Harbaugh

Purighalla VS, Raghavan ML, Harbaugh RE: Evaluation of the aspect ratio of cerebral aneurysms as a predictor of rupture, in 2000 Annual Meeting, American Association of Neurological Surgeons. San Francisco, CA. Park Ridge, IL: American Association of Neurological Surgeons, 2000

Curvature approximation for triangulated surfaces Geometric Modelling , Computing Suppl 8

Jan 1993
139-153

B Hamann

Hamann B: Curvature approximation for triangulated surfaces, in Farin G, Hagen H, Noltemeier H (eds): Geometric Modelling, Computing Suppl 8. New York: Springer-Verlag, 1993, pp 139–153

Accepted in final form This work was supported by the Cordis Basic Science Award in Neurovascular Disease Address reprint requests to

Jul 2004

Manuscript received June 20, 2004. Accepted in final form September 23, 2004. This work was supported by the Cordis Basic Science Award in Neurovascular Disease, 2004. Address reprint requests to: Robert E. Harbaugh, M.D., Room 3830, Biomedical Research Building, Penn State Hershey Medical Center, 500 University Drive, Hershey, Pennsylvania 17003. email: rharbaugh@psu.edu.

London: King's College

Adc Smith

Quantified aneurysm shape and rupture risk

Abstract

No full-text available

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