Circle of Willis configuration as a determinant of intracranial dolichoectasia

Association of brain arterial diameters with demographic and anatomical factors in a multi-national pooled analysis of cohort studies

BACKGROUND AND PURPOSE

Brain arterial diameters are markers of cerebrovascular disease. Demographic and anatomical factors may influence arterial diameters. We hypothesize that age, sex, height, total cranial volume (TCV), and persistent fetal posterior cerebral artery (fPCA) correlate with brain arterial diameters across populations.

METHODS

Participants had a time-of-flight MRA from nine international cohorts. Arterial diameters of the cavernous internal carotid arteries (ICA), middle cerebral arteries (MCA), and basilar artery (BA) were measured using LAVA software. Regression models assessed the association between exposures and brain arterial diameters.

RESULTS

We included 6,518 participants (mean age: 70 ± 9 years; 41% men). Unilateral fPCA was present in 13.2% and bilateral in 3.2%. Larger ICA, MCA, and BA diameters correlated with older age (Weighted average [WA] per 10 years: 0.18 mm, 0.11 mm, and 0.12 mm), male sex (WA: 0.24 mm, 0.13 mm, and 0.21 mm), and TCV (WA: for one TCV standard deviation: 0.24 mm, 0.29 mm, and 0.18 mm). Unilateral and bilateral fPCAs showed a positive correlation with ICA diameters (WA: 0.39 mm and 0.73 mm) and negative correlation with BA diameters (WA: -0.88 mm and -1.73 mm). Regression models including age, sex, TCV, and fPCA explained on average 15%, 13%, and 25% of the ICA, MCA, and BA diameter interindividual variation, respectively. Using height instead of TCV as a surrogate of head size decreased the R-squared by 3% on average.

CONCLUSION

Brain arterial diameters correlated with age, sex, TCV, and fPCA. These factors should be considered when defining abnormal diameter cutoffs across populations.

Pathology-based brain arterial disease phenotypes and their radiographic correlates

INTRODUCTION

Brain arterial diseases, including atherosclerosis, vasculitis, and dissections, are major contributors to cerebrovascular morbidity and mortality worldwide. These diseases not only increase the risk of stroke but also play a significant role in neurodegeneration and dementia. Clear and unambiguous terminology and classification of brain arterial disease phenotypes is crucial for research and clinical practice.

MATERIAL AND METHODS

This review aims to summarize and harmonize the terminology used for brain large and small arterial phenotypes based on pathology studies and relate them to imaging phenotypes used in medical research and clinical practice.

CONCLUSIONS AND RESULTS

Arteriosclerosis refers to hardening of the arteries but does not specify the underlying etiology. Specific terms such as atherosclerosis, calcification, or non-atherosclerotic fibroplasia are preferred. Atherosclerosis is defined pathologically by an atheroma. Other brain arterial pathologies occur and should be distinguished from atherosclerosis given therapeutic implications. On brain imaging, intracranial arterial luminal stenosis is usually attributed to atherosclerosis in the presence of atherosclerotic risk factors but advanced high-resolution arterial wall imaging has the potential to more accurately identify the underlying pathology. Regarding small vessel disease, arteriosclerosis is ambiguous and arteriolosclerosis is often used to denote the involvement of arterioles rather than arteries. Lipohyalinosis is sometimes used synonymously with arteriolosclerosis, but less accurately describes this common small vessel thickening which uncommonly shows lipid. Specific measures of small vessel wall thickness, the relationship to the lumen as well as changes in the layer composition might convey objective, measurable data regarding the status of brain small vessels.

Epidemiology, Pathophysiology, and Imaging of Atherosclerotic Intracranial Disease

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of stroke worldwide. Among people with stroke, those of East Asia descent and non-White populations in the United States have a higher burden of ICAD-related stroke compared with Whites of European descent. Disparities in the prevalence of asymptomatic ICAD are less marked than with symptomatic ICAD. In addition to stroke, ICAD increases the risk of dementia and cognitive decline, magnifying ICAD societal burden. The risk of stroke recurrence among patients with ICAD-related stroke is the highest among those with confirmed stroke and stenosis ≥70%. In fact, the 1-year recurrent stroke rate of >20% among those with stenosis >70% is one of the highest rates among common causes of stroke. The mechanisms by which ICAD causes stroke include plaque rupture with in situ thrombosis and occlusion or artery-to-artery embolization, hemodynamic injury, and branch occlusive disease. The risk of stroke recurrence varies by the presumed underlying mechanism of stroke, but whether techniques such as quantitative magnetic resonance angiography, computed tomographic angiography, magnetic resonance perfusion, or transcranial Doppler can help with risk stratification beyond the degree of stenosis is less clear. The diagnosis of ICAD is heavily reliant on lumen-based studies, such as computed tomographic angiography, magnetic resonance angiography, or digital subtraction angiography, but newer technologies, such as high-resolution vessel wall magnetic resonance imaging, can help distinguish ICAD from stenosing arteriopathies.

Association of Brain Arterial Elongation With Risk of Stroke and Death in Stroke-Free Individuals: Results From NOMAS

BACKGROUND

Brain arterial dilation and elongation characterize dolichoectasia, an arteriopathy associated with risk of stroke and death. We aim to determine whether brain arterial elongation increases the risk of stroke and death independent of brain arterial diameters.

METHODS

We analyzed 1210 stroke-free participants (mean age 71±9 years, 41% men, 65% Hispanic) with available time-of-flight magnetic resonance angiogram from the Northern Manhattan Study, a population-based cohort study across a multiethnic urban community. We obtained baseline middle cerebral artery M1-segment (MCA-M1) and basilar artery (BA) mean lengths and diameters using a semi-automated software. Cox proportional hazards models adjusted for brain arterial diameters and potential confounders yielded adjusted hazards ratios with 95% CIs for the primary outcomes of incident stroke and all-cause mortality, as well as secondary outcomes including noncardioembolic stroke, vascular death, and any vascular event.

RESULTS

Neither MCA-M1 nor BA lengths correlated with incident stroke or all-cause mortality. Both MCA-M1 and BA larger diameters correlated with all-cause mortality (MCA-M1 aHR, 1.52 [95% CI, 1.03-2.23], BA aHR, 1.28 [95% CI, 1.02-1.61]), as well as larger MCA-M1 diameters with vascular death (aHR, 1.84 [95% CI, 1.02-3.31]). Larger MCA-M1 and BA diameters did not correlate with incident stroke. However, larger BA diameters were associated with posterior circulation noncardioembolic stroke (aHR, 2.93 [95% CI, 1.07-8.04]). There were no statistical interactions between brain arterial lengths and diameters in relation to study outcomes.

CONCLUSIONS

In a multiethnic cohort of stroke-free adults, brain arterial elongation did not correlate with risk of stroke or death, nor influenced the significant association between brain arterial dilation and vascular risk.

Effects of abnormal vertebral arteries and the circle of Willis on vertebrobasilar dolichoectasia: A multi-scale simulation study

BACKGROUND

Vertebrobasilar dolichoectasia is a rare cerebrovascular disease characterized by obvious extension, dilation and tortuosity of vertebrobasilar artery, and its pathophysiological mechanism is not clear. This study focused on local hemodynamic changes in basilar arteries with typical vertebrobasilar dolichoectasia, together with unbalanced vertebral arteries and abnormal structures of the circle of Willis, through multi-scale modeling.

METHODS

Three-dimensional models of 3 types of vertebrobasilar arteries were constructed from magnetic resonance images. The first type has no vertebrobasilar dolichoectasia, the second type has vertebrobasilar dolichoectasia and balanced vertebral arteries, and the third type has vertebrobasilar dolichoectasia and unbalanced vertebral arteries. A lumped parameter model of the circle of Willis was established and coupled to these three-dimensional models.

FINDINGS

The results showed that unbalanced bilateral vertebral arteries, especially single vertebral artery deletion mutation, might associate with higher wall shear stress on anterior wall of basilar artery in patients with vertebrobasilar dolichoectasia. And unbalanced bilateral vertebral arteries would increase the blood pressure in basilar artery. Meanwhile, missing communicating arteries in the circle of Willis, especially bilateral posterior communicating arteries absences, would significantly increase blood pressure in basilar artery. The unilateral absence of posterior communicating arteries would increase differences in blood flow between the left and right posterior cerebral arteries.

INTERPRETATION

This study provided a multi-scale modeling method and some preliminary results for helping understand the role of hemodynamics in occurrence and development of vertebrobasilar dolichoectasia.

Anatomical effects on the relationship between brain arterial diameter and length: The Northern Manhattan Study

BACKGROUND AND PURPOSE

In patients with dolichoectasia, it is uncertain how dilatation and/or elongation relate to each other. We aimed to examine the correlation between arterial diameter and length within arteries and across the circle of Willis (COW).

METHODS

We included stroke-free participants in the Northern Manhattan Study who underwent magnetic resonance angiography. Intracranial artery diameters and lengths were obtained with semiautomated commercial software and were adjusted for head size. We first investigated the correlation between diameters and length using Pearson's correlation coefficient. We then built generalized linear models adjusted for demographics and risk factors.

RESULTS

Among 1210 participants included in the analysis (mean age 71 ± 9 years, 59% women, 65% Hispanic), a larger basilar artery (BA) diameter correlated with greater BA length (r = .3), and left and right middle cerebral artery (MCA) diameters correlated with one another (r = .4). Across the COW, BA diameter correlated with MCA diameters (r = .3 for both). In adjusted analyses, MCA diameters were associated with larger posterior circulation diameters (β = 0.07), MCA and BA lengths (β = 0.003 and β = 0.002, respectively), presence of fetal posterior cerebral artery (PCA), (β = 0.11), and a complete COW (β = -0.02). Similarly, BA length was associated with a fetal PCA (β = 1.1), and BA diameter was associated with anterior circulation diameters (β = 0.15) and presence of fetal PCA (β = -0.4).

CONCLUSIONS

COW configuration should be considered when using arterial diameter cutoffs to define dolichoectasia. Further studies are needed to discern whether arterial diameter or length best identify individuals at risk of vascular events attributable to dolichoectasia.

Arterial Stiffness is Associated with Intracranial Arterial Stenosis other than Dolichoectasia in the General Population

Aims: The relationship between central arterial stiffness and aging-related intracranial arteriopathy is not well investigated in the general population. In a population-based study, we investigated arterial stiffness in relation to intracranial atherosclerotic stenosis and intracranial arterial dolichoectasia.

Methods: This study was a cross-sectional analysis on 1,123 subjects (aged 56.0 ± 9.3 years, 37.9% men) of the population-based Shunyi study in China. Arterial stiffness was assessed by measuring brachial-ankle pulse wave velocity (baPWV). Intracranial atherosclerotic stenosis and intracranial arterial dolichoectasia were evaluated via brain magnetic resonance angiography. Multivariate regression models were constructed to investigate the association between baPWV and intracranial large artery diseases.

Results: Increased baPWV was significantly associated with higher prevalence of intracranial atherosclerotic stenosis (odds ratio for the highest quartile of baPWV compared with the lowest quartile, 3.66 [95% confidence interval, 1.57–8.54]), after adjustment for cardiovascular risk factors in multivariate analysis. BaPWV was not associated with the presence of basilar artery dolichoectasia and dilation of basilar artery and internal carotid artery. When the diameters of intracranial arteries were regarded as continuous variables, increased baPWV was inversely related to the internal carotid artery diameter in fully adjusted models (β ± SE, −0.083 ± 0.042, p = 0.047).

Conclusions: This population-based study demonstrates that arterial stiffness was more likely associated with intracranial stenotic arteriopathy other than intracranial dilative arteriopathy.

A 5-Year Follow-up of Intracranial Arterial Dolichoectasia: A Case Report and Review of Literature

A patient with multiple dolichoectasia of the intracranial cerebral artery was followed sequentially with clinical and radiological progression of disease in the past 5 years. The patient was treated in multiple stages in the past 5 years with the endovascular and microsurgical clipping method. The maximum diameter of each major intracranial artery segment was recorded and compared in the follow-up year. The progression in size of the dolichoectatic segment was observed in spite of surgical intervention. In review diagnostic criteria, etiopathogenesis and treatment options have been discussed.

Are the Variants of the Circle of Willis Determined by Genetic or Environmental Factors? Results of a Twin Study and Review of the Literature

BACKGROUND

Anatomic variants of the circle of Willis (CW) are commonly observed in healthy subjects. Genetic and environmental factors influencing these variants remain unclear. Our aim was to assess the genetic and environmental background affecting variant CW phenotypes.

METHODS

A total of 122 adult healthy twins from the Hungarian Twin Registry (39 monozygotic (MZ) and 22 dizygotic (DZ) pairs, average age 49.7 ± 13.4 years) underwent Time-of-Flight magnetic resonance angiography and transcranial Doppler sonography. We investigated the anterior and posterior CW according to morphological categories. Prevalence and concordance rates of CW variants were calculated. MZ twins discordant for CW variants were analyzed for cardiovascular risk factors and altered blood flow.

RESULTS

Complete CW (45.0%) and bilaterally absent posterior communicating artery (PCoA) (22.5%) were the most prevalent variants in the anterior and posterior CW, respectively. There was no significant difference regarding the prevalence of variants across zygosity except for bilaterally hypoplastic PCoA (p = .02). DZ concordance was higher compared to MZ twins regarding morphological categories of the CW. Cardiovascular risk factors were not significantly associated with variant CW in MZ twins discordant to CW morphology. Flow parameters did not differ significantly among MZ twins discordant to CW variants.

CONCLUSION

CW variants may not be determined by substantial genetic effects and are not influenced by altered blood flow in healthy individuals. Further investigations are needed to identify potential environmental factors affecting these variants.

Intracranial Arterial Dolichoectasia and Stenosis

Background and Purpose—

Intracranial arterial dolichoectasia (IADE) is a poorly understood arteriopathy compared with intracranial atherosclerotic stenosis (ICAS). We aimed to investigate the risk factors of IADE and ICAS and their relationship with neuroimaging markers of cerebral small vessel disease in a population-based study.

Methods—

This study comprised 1237 participants (aged 57.2±9.4 years, 37.6% men) who underwent brain magnetic resonance imaging and magnetic resonance angiography. IADE was assessed based on basilar artery dolichoectasia (diameter, height of bifurcation, and laterality of basilar artery) and dilation of basilar artery and internal carotid artery (intracranial volume-adjusted diameter ≥2 SD). ICAS was defined as any degree of stenosis in at least 1 intracranial artery. The neuroimaging markers of cerebral small vessel disease, including lacunes, white matter hyperintensities, microbleeds, dilated perivascular spaces, and brain atrophy, were evaluated.

Results—

Basilar arterial dolichoectasia was observed in 3.6% (45/1237); intracranial arterial dilation in 5.9% (67/1142); and ICAS in 15.7% (194/1237). Older age, higher systolic blood pressure, diabetes mellitus, higher LDL-C (low-density lipoprotein cholesterol) and lower HDL-C (high-density lipoprotein cholesterol) were associated with the presence of ICAS (all P <0.001), whereas only older age was associated with IADE. ICAS was associated with lacunes (odds ratio, 2.91; 95% confidence interval, 1.96–4.34; P <0.001), increased white matter hyperintensities volume (β±SE, 0.54±0.13; P <0.001), and brain atrophy (β±SE, −1.16±0.21; P <0.001), whereas basilar arterial dolichoectasia was mainly associated with dilated perivascular spaces in basal ganglia (odds ratio, 2.20; 95% confidence interval, 1.20–4.02; P =0.01) and, to a lesser extent, associated with lacunes and microbleeds.

Conclusions—

IADE and ICAS had different risk factor profiles and associated with different imaging phenotypes of cerebral small vessel disease, suggesting different underlying mechanisms.

Brain Arterial Diameters and Cognitive Performance: The Northern Manhattan Study

OBJECTIVES

To test the hypothesis that brain arterial diameters are associated with cognitive performance, particularly in arteries supplying domain-specific territories.

METHODS

Stroke-free participants in the Northern Manhattan Study were invited to have a brain MRI from 2003-2008. The luminal diameters of 13 intracranial arterial segments were obtained using time-of-flight magnetic resonance angiogram (MRA), and then averaged and normalized into a global score and region-specific arterial diameters. Z-Scores for executive function, semantic memory, episodic memory and processing speed were obtained at MRI and during follow-up. Adjusted generalized additive models were used to assess for associations.

RESULTS

Among the 1034 participants with neurocognitive testing and brain MRI, there were non-linear relationships between left anterior (ACA) and middle cerebral artery (MCA) diameter and semantic memory Z-scores (χ2=10.00; DF=3; p=.019), and left posterior cerebral artery (PCA) and posterior communicating artery (Pcomm) mean diameter and episodic memory Z-scores (χ2=9.88; DF=3; p=.020). Among the 745 participants who returned for 2nd neuropsychological testing, on average 5.0±0.4 years after their MRI, semantic memory change was associated non-linearly with the left PCA/Pcomm mean diameter (χ2=13.09; DF=3; p=.004) and with the right MCA/ACA mean diameter (χ2=8.43; DF=3; p=.03). In both cross-sectional and longitudinal analyses, participants with the larger brain arterial diameters had more consistently lower Z-scores and greater decline than the rest of the participants.

CONCLUSIONS

Brain arterial diameters may have downstream effects in brain function presenting as poorer cognition. Identifying the mechanisms and the directionality of such interactions may increase the understanding of the vascular contribution to cognitive impairment and dementia. (JINS, 2018, 24, 335-346).

Ischemic stroke due to intracranial arterial dolichoectasia coexisting with spontaneous dissection of the basilar artery: A case report

INTRODUCTION

We present a rarely seen case of cerebral infarction due to intracranial dolichoectasia coexisting with spontaneous dissection of the basilar artery. A definition of dolichoectasia, its pathology, and imaging findings, as well as the clinical management and prognosis are briefly reviewed.

CONCLUSION

We discuss in general terms the diagnosis of basilar artery dissection and its probable relationship with the occurrence of dolichoectasia.

Anomalies and Normal Variants of the Cerebral Arterial Supply: A Comprehensive Pictorial Review with a Proposed Workflow for Classification and Significance

Cerebral arteries may exhibit a wide range of variation from normal anatomy, which can be incidentally discovered during imaging. Knowledge of such variants is crucial to differentiate them from pathologies, to understand the etiology of certain pathologies directly related to a vascular variant, and to depict the changes in collateral circulation in patients with certain variants. Detection of particular variants may lead to the discovery of other nonvascular or vascular anomalies, especially aneurysms, and may also affect planning of endovascular or neurosurgical interventions. In this review, we summarize the variants and anomalies of cerebral arteries seen on cross-sectional imaging classified by a morphological approach and categorize their significance from a clinical perspective. This structured review is intended to serve as a guide for daily use in clinical practice.

Basilar Artery Diameter Is Inversely Associated with Fetal Type Circle of Willis

BACKGROUND

The relationship between basilar artery (BA) diameter and Circle of Willis (CoW) configuration has been scarcely investigated. We aimed to assess this association in community-dwelling older adults.

METHODS

MRAs of 346 individuals were reviewed. Using generalized linear models adjusted for demographics and cardiovascular risk factors, we assessed the relationship between BA diameter and fetal and non-fetal types CoW, as well as the impact of this relationship on BA ectasia prevalence.

RESULTS

In the total population, the mean BA diameter was 3.13 ± 0.68 mm and 7 subjects (2%) had ectasia (BA diameter >4.5 mm). In 248 subjects with non-fetal types CoW, the mean BA diameter was 3.32 ± 0.62 mm, and 2.8% had ectasia. In 98 subjects with fetal type CoW, the mean BA diameter was 2.66 ± 0.58 mm, and no individual had ectasia. The BA diameter was smaller in subjects with fetal type CoW than in those with non-fetal types (β 0.65; 95% CI 0.51-0.79; p < 0.001). Individuals with fetal type CoW have an 18% reduction in BA diameter compared to those with non-fetal types, independently of demographics and cardiovascular risk factors.

CONCLUSION

This study shows an inverse relationship between the BA diameter and the presence of fetal type CoW.

A case of intracranial arterial dolichoectasia with 4 repeated cerebral infarctions in 6 months and enlargement of basilar artery

A 78-year-old man was admitted to our hospital because of sudden right hemiparesis and dysarthria. His cranial MRI showed an area of hyperintensity in left pons on DWI and MRA revealed dilated, elongated and tortuous intracranial artery. We diagnosed as acute phase ischemic stroke and intracranial arterial dolichoectasia (IADE). Intravenous infusion of rt-PA was performed 157 minutes after the onset of symptoms, and his hemiparesis improved. However, he subsequently suffered from cerebral infarction 4 times in 6 months, and we treated him twice with thrombolytic therapy. Although thrombolytic therapy was effective in the short term and antithrombotic therapy was continued, he had bilateral hemiplegia and severe dysphagia because of repeated cerebral infarctions. Hence basilar artery was dilated with intramural hemorrhage over 6 months, and we discontinued antithrombolytic therapy. It is possible that antithrombolytic therapy affects enlargement of IADE. Antithrombolytic therapy for IADE should be done carefully.

Brain arterial aging and its relationship to Alzheimer dementia

OBJECTIVE

To test the hypothesis that brain arterial aging is associated with the pathologic diagnosis of Alzheimer disease (AD).

METHODS

Brain large arteries were assessed for diameter, gaps in the internal elastic lamina (IEL), luminal stenosis, atherosclerosis, and lumen-to-wall ratio. Elastin, collagen, and amyloid were assessed with Van Gieson, trichrome, and Congo red staining intensities, and quantified automatically. Brain infarcts and AD (defined pathologically) were assessed at autopsy. We created a brain arterial aging (BAA) score with arterial characteristics associated with aging after adjusting for demographic and clinical variables using cross-sectional generalized linear models.

RESULTS

We studied 194 autopsied brains, 25 (13%) of which had autopsy evidence of AD. Brain arterial aging consisted of higher interadventitial and lumen diameters, thickening of the wall, increased prevalence of IEL gaps, concentric intima thickening, elastin loss, increased amyloid deposition, and a higher IEL proportion without changes in lumen-to-wall ratio. In multivariable analysis, a high IEL proportion (B = 1.96, p = 0.030), thick media (B = 3.50, p = 0.001), elastin loss (B = 6.16, p < 0.001), IEL gaps (B = 3.14, p = 0.023), and concentric intima thickening (B = 7.19, p < 0.001) were used to create the BAA score. Adjusting for demographics, vascular risk factors, atherosclerosis, and brain infarcts, the BAA score was associated with AD (B = 0.022, p = 0.002).

CONCLUSIONS

Aging of brain large arteries is characterized by arterial dilation with a commensurate wall thickening, elastin loss, and IEL gaps. Greater intensity of arterial aging was associated with AD independently of atherosclerosis and brain infarcts. Understanding the drivers of arterial aging may advance the knowledge of the pathophysiology of AD.

Pathophysiology, presentation, prognosis, and management of intracranial arterial dolichoectasia

Up to 12% of patients with stroke have intracranial arterial dolichoectasia (IADE) and the basilar artery is affected in 80% of these cases. Diagnostic criteria and prognosis studies of IADE are based on basilar artery diameter, which is a good quantitative marker for the severity of the disease. The pathophysiology is largely unknown, but IADE can be viewed as a common final pathway of arterial wall response or damage in the tunica media due to various mechanisms, such as matrix metalloproteinase dysfunction or muscle cell or elastic fibre injury. No randomised controlled trials have been undertaken in IADE and thus little high-level evidence is available on which to base treatment guidelines. IADE management depends on clinical presentation and disease severity, and includes blood pressure control, antithrombotic treatments, endovascular procedures, and surgery. Further studies are needed to better define IADE in the general population, to establish its prevalence and pathophysiology, to identify subgroups at risk of life-threatening complications, and to offer effective treatment options.

Brain Arterial Diameters as a Risk Factor for Vascular Events

Background

Arterial luminal diameters are routinely used to assess for vascular disease. Although small diameters are typically considered pathological, arterial dilatation has also been associated with disease. We hypothesize that extreme arterial diameters are biomarkers of the risk of vascular events.

Methods and Results

Participants in the Northern Manhattan Study who had a time-of-flight magnetic resonance angiography were included in this analysis (N=1034). A global arterial Z-score, called the brain arterial remodeling (BAR) score, was obtained by averaging the measured diameters within each individual. Individuals with a BAR score <−2 SDs were considered to have the smallest diameters, individuals with a BAR score >−2 and <2 SDs had average diameters, and individuals with a BAR score >2 SDs had the largest diameters. All vascular events were recorded prospectively after the brain magnetic resonance imaging. Spline curves and incidence rates were used to test our hypothesis. The association of the BAR score with death (P=0.001), vascular death (P=0.02), any vascular event (P=0.05), and myocardial infarction (P=0.10) was U-shaped except for ischemic stroke (P=0.74). Consequently, incidence rates for death, vascular death, myocardial infarction, and any vascular event were higher in individuals with the largest diameters, whereas individuals with the smallest diameters had a higher incidence of death, vascular death, any vascular event, and ischemic stroke compared with individuals with average diameters.

Conclusions

The risk of death, vascular death, and any vascular event increased at both extremes of brain arterial diameters. The pathophysiology linking brain arterial remodeling to systemic vascular events needs further research.

A Functional Perspective on the Embryology and Anatomy of the Cerebral Blood Supply

The anatomy of the arterial system supplying blood to the brain can influence the development of arterial disease such as aneurysms, dolichoectasia and atherosclerosis. As the arteries supplying blood to the brain develop during embryogenesis, variation in their anatomy may occur and this variation may influence the development of arterial disease. Angiogenesis, which occurs mainly by sprouting of parent arteries, is the first stage at which variations can occur. At day 24 of embryological life, the internal carotid artery is the first artery to form and it provides all the blood required by the primitive brain. As the occipital region, brain stem and cerebellum enlarge; the internal carotid supply becomes insufficient, triggering the development of the posterior circulation. At this stage, the posterior circulation consists of a primitive mesh of arterial networks that originate from projection of penetrators from the distal carotid artery and more proximally from carotid-vertebrobasilar anastomoses. These anastomoses regress when the basilar artery and the vertebral arteries become independent from the internal carotid artery, but their persistence is not uncommon in adults (e.g., persistent trigeminal artery). Other common remnants of embryological development include fenestration or duplication (most commonly of the basilar artery), hypoplasia (typically of the posterior communicating artery) or agenesis (typically of the anterior communicating artery). Learning more about the hemodynamic consequence that these variants may have on the brain territories they supply may help understand better the underlying physiopathology of cerebral arterial remodeling and stroke in patients with these variants.

A pathological perspective on the natural history of cerebral atherosclerosis

BACKGROUND

The natural history of intracranial large artery atherosclerosis has been mainly described from lumen-based imaging studies, and much of what is reported to be known about atherosclerosis is derived from non-cerebral arteries.

AIMS

To test the hypothesis that atherosclerosis is only partially represented by stenosis and that advanced atherosclerosis is more common that severe stenosis in noncardioembolic infarcts.

METHODS

Cerebral large arteries from 196 autopsy cases were studied. The revised American Heart Association classification for atherosclerosis was used to determine the phenotype in each available artery. Cross-sectional lumen stenosis was obtained as defined by the Glagov's method.

RESULTS

As age of cases increased, there was a progressive increment in the frequency of atherosclerotic lesions, rising from 5% of all arteries at age 20-40, to more than 40% at age 60 or older. Stenosis also increased with age: less than 3% of the arteries in those ≤50 years had >40% stenosis, while one out of five arteries in those >80 years had >40% stenosis. In most cases (80%), atherosclerosis and stenosis were directly related. However, one out of five cases with advanced atherosclerosis had <30% stenosis. In arteries supplying brain areas with noncardioembolic infarcts, the majority of segments exhibiting advanced atherosclerosis had lumen stenosis of <40%.

CONCLUSION

Although intracranial atherosclerosis is typically associated with stenosis, a substantial minority of cases shows advanced atherosclerosis in the absence of stenosis >40%. Definitions based solely on stenosis may underestimate the extent and role of intracranial large artery atherosclerosis.

Dolichoectasia and the risk of stroke and vascular disease: a critical appraisal

Dolichoectasia (DE) in cerebral arteries is a poorly understood arteriopathy that has been associated with increased risk of vascular morbidity and mortality. Dolichoectasia tends to affects older individuals with vascular risk factors, but it can also be secondary to specific conditions related with extracellular matrix health. The range of methods used to study DE and the biases inherent to hospital-based samples weaken the generalizability of DE study results to the general population. Within the context of these limitations, there is growing evidence that DE is a serious condition that can increase the risk of vascular death. Recurrent strokes and compressive symptoms are among the major causes of morbidity, but cardiac ischemic disease and aortic aneurysms are not uncommon in populations with DE. The devastating outcomes of patients with DE are a call to action aimed at improving the quality of research on the topic and discovering therapies that can palliate the burden of DE in the population.

Compensatory intracranial arterial dilatation in extracranial carotid atherosclerosis: the Northern Manhattan study

BACKGROUND

There is a scarcity of data supporting the association between atherosclerosis and dolichoectasia in unbiased samples.

AIMS

To test the hypothesis that the association between dolichoectasia and extracranial carotid atherosclerosis depends on the degree of collateral circulation.

METHODS

The Northern Manhattan Study magnetic resonance imaging substudy consists of 1290 participants who remained stroke-free at the time of magnetic resonance imaging. Arterial diameters were collected in all participants with available magnetic resonance angiography. Dolichoectasia was defined as a head-size adjusted diameter >2 standard deviation for each artery. Carotid Doppler was used to evaluate for carotid atherosclerosis (carotid plaque, maximum plaque thickness and carotid intima media thickness).

RESULTS

We included 994 participants with available Doppler and magnetic resonance angiography data (mean age 63 years, 60% female). Any dolichoectasia was reported in 16% of participants, 54% had at least one carotid plaque and the mean carotid intima media thickness was 0·92 ± 0·09 mm. After adjusting for demographic and clinical characteristics, there was no association between markers of carotid atherosclerosis and dolichoectasia. However, stratifying by collaterals, it was observed that dolichoectasia was more likely in the anterior and posterior circulations when collaterals were available among participants with carotid atherosclerosis. These associations were confirmed by noting an increment in arterial diameters in the corresponding arteries ipsilateral and contralateral to each carotid as well as in the posterior circulation.

CONCLUSIONS

We did not find an association of extracranial carotid atherosclerosis with dolichoectasia. However, we found that dolichoectasia is more frequent when intracranial collaterals are available suggesting a compensatory process that needs further investigation.

Determinants of cerebrovascular remodeling: do large brain arteries accommodate stenosis?

OBJECTIVE

It is hypothesized that outward remodeling in systemic arteries is a compensatory mechanism for lumen area preservation in the face of increasing arterial stenosis. Large brain arteries have also been studied, but it remains unproven if all assumptions about arterial remodeling can be replicated in the cerebral circulation.

METHODS

The sample included 196 autopsied subjects with a mean age of 55 years; 63 % were men, and 74 % non-Hispanic whites. From each of 1396 dissected cadaveric large arteries of the circle of Willis, the areas of the lumen, intima, media, and adventitia were measured. Internal elastic lamina (IEL) area was defined as the area encircled by this layer. Stenosis was calculated by dividing the plaque area by the IEL area and multiplying by 100.

RESULTS

Plotting stenosis against lumen area or stratified by arterial size showed no preservation of the lumen in the setting of growing stenosis. We could not find an association between greater IEL proportion and stenosis (B = 0.44, P = 0.86). Stratifying arteries by their size, we found that smaller arteries have greater lumen reduction at any degree of stenosis (B = -23.65, P ≤ 0.0001), and although larger arteries show a positive association between IEL proportion and stenosis, this was no longer significant after adjusting for covariates (B = 6.0, P = 0.13).

CONCLUSIONS

We cannot confirm the hypothesis that large brain arteries undergo outward remodeling as an adaptive response to increasing degrees of stenosis. We found that the lumen decreases proportionally to the degree of stenosis.

A quantitative perspective to the study of brain arterial remodeling of donors with and without HIV in the Brain Arterial Remodeling Study (BARS)

Mechanisms underlying brain arterial remodeling are uncertain. We tested the hypothesis that arterial size and location are important determinants of arterial characteristics. We collected large and penetrating brain arteries from cadavers with and without HIV. Morphometric characterization was obtained from digital images using color-based thresholding. The association of arterial size and location with lumen diameter, media and adventitia area, media proportion, a wall thickness, wall-to-lumen ratio and stenosis was obtained with multilevel mixed models and a P value ≤ 0.05 was considered significant. We included 336 brains, in which 2279 large arteries and 1488 penetrating arteries were identified. We found that arterial size was significantly associated with all arterial characteristics studied of large and penetrating arteries with exception of arterial stenosis in large arteries. After adjusting for size, an independent association was found between lumen diameters, media and adventitia thickness with artery locations. Arterial stenosis was also associated with artery location in both large and penetrating arteries. In summary, significant effects of size and/or location were found in arterial characteristics typically used to define arterial remodeling. Brain arterial remodeling characteristics differ across arterial sizes and location, and these differences should be controlled for in future studies of brain arterial remodeling.