Characterizing Tissue Remodeling and Mechanical Heterogeneity in Cerebral Aneurysms.

Accurately assessing the complex tissue mechanics of cerebral aneurysms (CAs) is critical for elucidating how CAs grow and whether that growth will lead to rupture. The factors that have been implicated in CA progression - blood flow dynamics, immune infiltration, and extracellular matrix remodeling - all occur heterogeneously throughout the CA. Thus, it stands to reason that the mechanical properties of CAs are also spatially heterogeneous. Here, we present a new method for characterizing the mechanical heterogeneity of human CAs using generalized anisotropic inverse mechanics, which uses biaxial stretching experiments and inverse analyses to determine the local Kelvin moduli and principal alignments within the tissue. Using this approach, we find that there is significant mechanical heterogeneity within a single acquired human CA. These results were confirmed using second harmonic generation imaging of the CA's fiber architecture and a correlation was observed. This approach provides a single-step method for determining the complex heterogeneous mechanics of CAs, which has important implications for future identification of metrics that can improve accuracy in prediction risk of rupture.

Occult blood flow patterns distal to an occluded artery in acute ischemic stroke.

Residual blood flow distal to an arterial occlusion in patients with acute ischemic stroke (AIS) is associated with favorable patient outcome. Both collateral flow and thrombus permeability may contribute to such residual flow. We propose a method for discriminating between these two mechanisms, based on determining the direction of flow in multiple branches distal to the occluding thrombus using dynamic Computed Tomography Angiography (dynamic CTA). We analyzed dynamic CTA data of 30 AIS patients and present patient-specific cases that identify typical blood flow patterns and velocities. We distinguished patterns with anterograde (N = 10), retrograde (N = 9), and both flow directions (N = 11), with a large variability in velocities for each flow pattern. The observed flow patterns reflect the interplay between permeability and collaterals. The presented method characterizes distal flow and provides a tool to study patient-specific distal tissue perfusion.

Influence of nimodipine combined with ulinastatin on neurological function and inflammatory reaction in patients with cerebral vasospasm after subarachnoid hemorrhage.

OBJECTIVE: This study aimed to discuss the influence of nimodipine+ulinastatin on the neurological function and inflammatory reaction in patients with cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH). METHODS: Overall, 90 patients with CVS after SAH who were admitted to our hospital were enrolled in this study and randomly divided into research and control groups (n = 45 for both groups). On the basis of conventional therapy, patients in the control group were injected with ulinastatin and those in the research group were injected with ulinastatin+nimodipine through an intravenous drip for 7 days with the others the same as those of the control group. RESULTS: Blood flow velocity in all cerebral arteries was lower in the research group than in the control group after treatment (P < 0.05). Calcitonin gene-related peptide and nitric oxide levels were higher in the research group than in the control group after treatment (P < 0.05). Endothelin levels were lower in the research group than in the control group (P < 0.05). The total effective rate was higher in the research group than in the control group (P < 0.05). Glasgow Coma Scale scores were higher in the research group than in the control group (P < 0.05). CONCLUSION: The drug combination of nimodipine and ulinastatin improved blood flow and neurological function in patients with CVS after SAH and enhanced the therapeutic efficacy; the underlying mechanism may be associated with the regulation of vascular endothelial dilatation function and the inhibition of relevant inflammatory factors' expression.

Immune Cells Invade the Collateral Circulation during Human Stroke: Prospective Replication and Extension.

It remains unclear if principal components of the local cerebral stroke immune response can be reliably and reproducibly observed in patients with acute large-vessel-occlusion (LVO) stroke. We prospectively studied a large independent cohort of n = 318 consecutive LVO stroke patients undergoing mechanical thrombectomy during which cerebral blood samples from within the occluded anterior circulation and systemic control samples from the ipsilateral cervical internal carotid artery were obtained. An extensive protocol was applied to homogenize the patient cohort and to standardize the procedural steps of endovascular sample collection, sample processing, and laboratory analyses. N = 58 patients met all inclusion criteria. (1) Mean total leukocyte counts were significantly higher within the occluded ischemic cerebral vasculature (I) vs. intraindividual systemic controls (S): +9.6%, I: 8114/µL ± 529 vs. S: 7406/µL ± 468, p = 0.0125. (2) This increase was driven by neutrophils: +12.1%, I: 7197/µL ± 510 vs. S: 6420/µL ± 438, p = 0.0022. Leukocyte influx was associated with (3) reduced retrograde collateral flow (R2 = 0.09696, p = 0.0373) and (4) greater infarct extent (R2 = 0.08382, p = 0.032). Despite LVO, leukocytes invade the occluded territory via retrograde collateral pathways early during ischemia, likely compromising cerebral hemodynamics and tissue integrity. This inflammatory response can be reliably observed in human stroke by harvesting immune cells from the occluded cerebral vascular compartment.

Reversible Cerebral Vasoconstriction Syndrome in Patients with Coronavirus Disease: A Multicenter Case Series.

BACKGROUND AND OBJECTIVES: RCVS (Reversible Cerebral Vasoconstrictive Syndrome) is a condition associated with vasoactive agents that alter endothelial function. There is growing evidence that endothelial inflammation contributes to cerebrovascular disease in patients with coronavirus disease 2019 (COVID-19). In our study, we describe the clinical features, risk factors, and outcomes of RCVS in a multicenter case series of patients with COVID-19. MATERIALS AND METHODS: Multicenter retrospective case series. We collected clinical characteristics, imaging, and outcomes of patients with RCVS and COVID-19 identified at each participating site. RESULTS: Ten patients were identified, 7 women, ages 21 - 62 years. Risk factors included use of vasoconstrictive agents in 7 and history of migraine in 2. Presenting symptoms included thunderclap headache in 5 patients with recurrent headaches in 4. Eight were hypertensive on arrival to the hospital. Symptoms of COVID-19 included fever in 2, respiratory symptoms in 8, and gastrointestinal symptoms in 1. One patient did not have systemic COVID-19 symptoms. MRI showed subarachnoid hemorrhage in 3 cases, intraparenchymal hemorrhage in 2, acute ischemic stroke in 4, FLAIR hyperintensities in 2, and no abnormalities in 1 case. Neurovascular imaging showed focal segment irregularity and narrowing concerning for vasospasm of the left MCA in 4 cases and diffuse, multifocal narrowing of the intracranial vasculature in 6 cases. Outcomes varied, with 2 deaths, 2 remaining in the ICU, and 6 surviving to discharge with modified Rankin scale (mRS) scores of 0 (n=3), 2 (n=2), and 3 (n=1). CONCLUSIONS: Our series suggests that patients with COVID-19 may be at risk for RCVS, particularly in the setting of additional risk factors such as exposure to vasoactive agents. There was variability in the symptoms and severity of COVID-19, clinical characteristics, abnormalities on imaging, and mRS scores. However, a larger study is needed to validate a causal relationship between RCVS and COVID-19.

Vascular contributions to cognitive impairment and dementia: the emerging role of 20-HETE.

The accumulation of extracellular amyloid-ß (Aß) and intracellular hyperphosphorylated τ proteins in the brain are the hallmarks of Alzheimer's disease (AD). Much of the research into the pathogenesis of AD has focused on the amyloid or τ hypothesis. These hypotheses propose that Aß or τ aggregation is the inciting event in AD that leads to downstream neurodegeneration, inflammation, brain atrophy and cognitive impairment. Multiple drugs have been developed and are effective in preventing the accumulation and/or clearing of Aß or τ proteins. However, clinical trials examining these therapeutic agents have failed to show efficacy in preventing or slowing the progression of the disease. Thus, there is a need for fresh perspectives and the evaluation of alternative therapeutic targets in this field. Epidemiology studies have revealed significant overlap between cardiovascular and cerebrovascular risk factors such as hypertension, diabetes, atherosclerosis and stroke to the development of cognitive impairment. This strong correlation has given birth to a renewed focus on vascular contributions to AD and related dementias. However, few genes and mechanisms have been identified. 20-Hydroxyeicosatetraenoic acid (20-HETE) is a potent vasoconstrictor that plays a complex role in hypertension, autoregulation of cerebral blood flow and blood-brain barrier (BBB) integrity. Multiple human genome-wide association studies have linked mutations in the cytochrome P450 (CYP) 4A (CYP4A) genes that produce 20-HETE to hypertension and stroke. Most recently, genetic variants in the enzymes that produce 20-HETE have also been linked to AD in human population studies. This review examines the emerging role of 20-HETE in AD and related dementias.

Computational Fluid Dynamics in Intracranial Atherosclerosis - Lessons from Cardiology: A Review of CFD in Intracranial Atherosclerosis.

BACKGROUND: Intracranial atherosclerosis is a common cause of stroke with a high recurrence rate. Haemodynamically significant lesions are associated with a particularly high risk of recurrence. Computational fluid dynamics (CFD) is a tool that has been investigated to identify haemodynamically significant lesions. CFD in the intracranial vasculature benefits from the precedent set by cardiology, where CFD is an established clinical tool. This precedent is particularly important in CFD as models are very heterogenous. There are many decisions-points in the model-creation process, usually involving a trade-off between computational expense and accuracy. OBJECTIVES: This study aimed to review published CFD models in intracranial atherosclerosis and compare them to those used in cardiology. METHODS: A systematic search for all published computational fluid dynamics models applied to intracranial atherosclerosis was performed. Each study was analysed as regards to the different steps in creating a fluid dynamics model and findings were compared with established cardiology CFD models. RESULTS AND CONCLUSION: 38 papers were screened and 12 were included in the final analysis. There were important differences between coronary and intracranial atherosclerosis models in the following areas: area of interest segmented, use of transient models vs steady-state models, boundary conditions, methods for solving the fluid dynamics equations and validation. These differences may be high-yield areas to explore for future research.

Reversible Cerebral Vasoconstriction Syndrome Following Exposure to Oleoresin Capsicum "Pepper Spray".

OBJECTIVES: To report a case associating the use of Oleoresin Capsicum Pepper Spray (OCPS) during law enforcement training with development of Reversible Cerebral Vasoconstriction Syndrome (RCVS). MATERIALS AND METHODS: RCVS is radiographically characterized by multifocal smooth narrowing of cerebral arteries heralded by clinical manifestations of recurrent thunderclap headaches. 70% of cases with RCVS have a clear precipitating factor and agents commonly implicated were cannabis, selective serotonin reuptake inhibitors, nasal decongestants, cocaine, postpartum state, eclampsia and strenuous physical/sexual activity.1 RESULTS: 24-year-old female police officer with no past medical history who presented with thunderclap headaches after exposure to pepper spray to her face during work training. Neurological examination was unremarkable. CT angiogram (CTA) of the head and neck and subsequent conventional angiogram revealed multifocal mild arterial narrowing of bilateral middle cerebral arteries (MCA), bilateral posterior cerebral arteries (PCA) and left anterior cerebral artery (ACA) concerning for RCVS. Eight weeks later, she had a repeat MRA head and neck demonstrating complete resolution of the previously noted narrowing of her cerebral arteries. CONCLUSIONS: OCPS is widely used in law enforcement training as well as by general population as a self- defense tool. It is generally assumed to be safe, although the consequences of its use can never be predicted with certainty.2 As our case highlights, use of OCPS may be associated with development of RCVS and awareness needs to be raised regarding this rare but serious complication.

Caloric restriction enhances vascular tone of cerebral and mesenteric resistance arteries in aged rats.

Vascular changes of tone and biomechanical properties induced by ageing increase the risk for cardiovascular diseases. Caloric restriction (CR) has been shown to protect against cardiovascular diseases and improve endothelial dysfunction in cerebral resistance arteries. We hypothesise that CR will enhance vascular tone and structural properties of cerebral resistance arteries and exert comparable beneficial effects on the systemic vasculature of aged rat model. Eighteen-month-old male Sprague-Dawley rats were feed either ad libitum or restricted to 60 % of calorie consumption up to 24 months of age, when body weight (BW) measurements were taken and functional and structural properties of resistance arteries were assessed using a pressure myograph. In cerebral arteries, CR increased myogenic tone (p < 0.001) and distensibility (p < 0.01) in response to intraluminal pressure and concentration-dependent constriction to KCl (p < 0.001). In mesenteric arteries constriction in response to KCl was increased (p < 0.0001) and wall thickness reduced (p < 0.01) in CR rats. BW was reduced (p < 0.0001) in FR rats. Our findings demonstrate that CR improves vascular tone of resistance arteries regardless the type of stimulus and independently of the vascular bed. CR may be a beneficial dietary approach to prevent age-related vascular diseases.

Quantitative laser speckle auto-inverse covariance imaging for robust estimation of blood flow.

We present a quantitative model to provide robust estimation of the decorrelation time using laser speckle auto-inverse covariance. It has the advantages of independence from the statistical sample size, speckle size, static scattering, and detector noise. We have shown cerebral blood flow imaging through an intact mouse skull using this model. Phantom experiments and two animal models, middle cerebral artery occlusion, and cortical spreading depression were used to evaluate its performance.

Advances in Understanding the Pathogenesis of Lacunar Stroke: From Pathology and Pathophysiology to Neuroimaging.

Lacunar stroke (LS) accounts for about one-quarter of all acute ischemic strokes, represents an important marker of cerebral small vessel disease (CSVD), and has prognostic significance in terms of recurrent vascular events and vascular cognitive impairment. Our understanding of the etiology and pathogenesis of LS is largely based on the meticulous postmortem work of C. Miller Fisher in the late 1960s, with scarce subsequent pathological analysis of the "lacunar hypothesis" and no reliable approaches for direct in vivo imaging of the small intracranial vessels. The recent development of high-resolution MRI, which allows both large-vessel wall and perforating arteries to be imaged in one setting, provides the opportunity to advance understandings of the clinical mechanisms, imaging characteristics, and pathogenesis of LS. Given accumulating evidence of endothelial dysfunction and blood-brain-barrier disruption as early features of CSVD-related LS, advanced imaging may allow various underlying pathogenetic mechanisms to be defined and for better targeting of therapeutic approaches in LS. In this review, progress in understanding the pathogenesis of LS is outlined, covering pathology, pathophysiology, and imaging characteristics, with a focus toward future directions in the complex entity of LS.

Childhood arterial ischemic stroke due to mineralizing angiopathy: an 18-year single-center experience.

Mineralizing angiopathy is a unique, age-specific stroke syndrome characterized by basal ganglia infarction and lenticulostriate calcification after minor head injury in early childhood. There is limited understanding of the pathophysiology, course, and clinical outcome of this syndrome. We describe the clinical and radiographical phenotype of a single-center, consecutively enrolled cohort of children with mineralizing angiopathy from January 2002 to January 2020 and provide a comparative analysis to previously published literature. Fourteen children were identified. Previously unreported findings include: stroke onset in eight children older than 18 months; presence of basal ganglia hemorrhage in four; multifocal basal ganglia infarcts in three; presence of additional non-basal ganglia calcifications in three; and presence of thrombophilia in one. Seven children had moderate-to-severe neurological deficits. There was no symptomatic stroke recurrence (mean follow-up 3y 7mo, SD 1y 7mo). Our expanded phenotype highlights distinct characteristics of mineralizing angiopathy in children and has the potential to inform future research. What this paper adds Children with mineralizing angiopathy are often misdiagnosed as having a limb fracture despite normal x-rays. A magnetic resonance imaging-only approach may miss this entity. Non-contrast computed tomography, in addition to MRI is recommended to identify calcifications in idiopathic arterial ischemic stroke. Most children have moderate-to-severe neurological sequela.

COVID-19 Associated Reversible Cerebral Vasoconstriction Syndrome Successfully Treated with Nimodipine and Aspirin.

There have been limited cases linking SARS-CoV-2 infection with the development of reversible cerebral vasoconstriction syndrome (RCVS). We hereby report a rare case of RCVS in the setting of mild SARS-CoV-2 respiratory infection successfully treated with nimodipine and aspirin. SARS-CoV-2 attacks the ACE2-receptors, which are expressed in various body organs including the lungs, kidneys, and blood vessels. Vasoconstriction can result from down-regulation of the ACE2-receptors that can lead to sympathetic hypertonia of the cerebral blood vessel walls and/or over-activation of the renin-angiotensin axis.

Pilot assessment of omega-3 fatty acids and potassium thiocyanate in sickle cell anemia patients with conditional peak systolic cerebral artery blood velocity.

OBJECTIVE: The purpose of this pilot study was to explore the effect of omega-3 fatty acids and potassium thiocyanate on conditional peak systolic cerebral artery blood velocity in children with sickle cell anemia (SCA). METHODS: Transcranial doppler ultrasonography (TCD) was done on 232 SCA children, and 21 found with conditional peak systolic blood velocity (PSV) of 200-249 cm/s in internal carotid, middle or anterior cerebral arteries. These were randomized to receive omega-3 fatty acids and potassium thiocyanate with standard treatment of SCA (test group, N = 14), or standard treatment only (control group, N = 7). After 3 months of treatment, PSV was measured again. RESULTS: Right middle cerebral artery PSV was significantly reduced in the test relative to the control groups (p = 0.04). PSV returned to normal in 79% of the test versus 43% of the control group; and increased to abnormal in one member of the control group, but none of the test group. CONCLUSIONS: The pilot data suggest that in SCA, omega-3 fatty acids and potassium thiocyanate might reduce conditional blood velocity to normal, or prevent progression to abnormal values. A larger, randomized, clinical trial is required to further address the current gap in management of conditional TCD blood velocity.

De Novo Dural Arteriovenous Fistula on Draining Veins of Previously Treated Pial Arteriovenous Malformation: a Case Report.

A 71-year-old man, with a pial micro-arteriovenous malformation (pAVM) draining into the confluence of the vein of Trolard and the vein of Labbé was surgically removed, sparing these cortical veins. 4-months MR and angiographic controls showed a de novo dural arteriovenous fistula (dAVF) draining into the previously spared cortical veins. It was removed using intraoperative motor evoked potentials (MEP). This is the first case of iatrogenic dAVF developing on the same draining vein of a previously treated pAVM. De novo dAVFs are generally iatrogenic. This case suggests that the unresected venous drainage of an AVM might be the substratum for neo-angiogenetic processes; moreover inflammation related to surgery might be the trigger factor for the development of the dAVF.

Relationship Between Central Artery Stiffness, Brain Arterial Dilation, and White Matter Hyperintensities in Older Adults: The ARIC Study-Brief Report.

[Figure: see text].

Enigma of what is Known about Intracranial Aneurysm Occlusion with Endovascular Devices.

Aneurysmal subarachnoid Hemorrhage is a major cause of neurological morbidity and mortality. Over the years vascular neurosurgery has witnessed technological advances aimed to reduce the morbidity and mortality. Several endovascular devices have been used in clinical practice to achieve this goal in the management of ruptured and unruptured cerebral aneurysms. Recurrence due to recanalization is encountered in all of these endovascular devices as well as illustrated by Barrow Ruptured Aneurysm Trial. Histological and molecular characterization of the aneurysms treated with endovascular devices is an area of active animal and human research studies. Yet, the pathobiology illustrating the mechanisms of aneurysmal occlusion and healing lacks evidence. The enigma of aneurysmal healing following treatment with endovascular devices needs to be de-mystified to understand the biological interaction of endovascular device and aneurysm and thereby guide the future development of endovascular devices aimed at better aneurysm occlusion. We performed a comprehensive and detailed literature review to bring all the known facts of the pathobiology of intracranial aneurysm healing, the knowledge of which is of paramount importance to neurosurgeons, an interventional neuroradiologist, molecular biologist, geneticists, and experts in animal studies. This review serves as a benchmark of what is known and platform for future studies basic science research related to intracranial aneurysms.

Cerebral Blood Flow in Chronic Kidney Disease.

The prevalence of mild cognitive impairment increases with age and is further exacerbated by chronic kidney disease (CKD). CKD is associated with (1) mild cognitive impairment, (2) impaired endothelial function, (3) impaired blood-brain barrier, (4) increased cerebral microhemorrhage burden, (5) increased cerebral blood flow (CBF), (6) impaired cerebral autoregulation, (7) impaired cerebrovascular reactivity, and (8) increased arterial stiffness. We report preliminary findings from our group that demonstrate altered cerebrovascular reactivity in a mouse model of CKD-associated vascular calcification. The CBF of CKD mice increased more quickly in response to hypercapnia (p < 0.05) but then decreased prematurely during hypercapnia challenge (p < 0.05). Together, these results indicate that altered kidney function can lead to alterations in the cerebral microvasculature, and hence brain health.

Changes in Angioarchitecture After Stereotactic Radiosurgery for Dural Arteriovenous Fistula.

INTRODUCTION: Dural arteriovenous fistulae (DAVF) are intracranial vascular abnormalities encountered in neurosurgery practice. Treatment options are microsurgical disconnection, endovascular embolization and/or radiosurgery. Past studies have reported the efficacy, safety, and predictors of success of radiosurgery. In this study, we investigated the angioarchitecture of fistulae at the time of radiosurgery and how the anatomy changed in the time after treatment based on angiogram follow-ups. METHODS: A retrospective analysis was performed on patients with angiographic diagnosis of DAVF treated with Gamma Knife radiosurgery (GKRS) between 2013 and 2018. Data collection included demographics, symptoms, grading scores, vascular anatomy, radiation data, treatment strategy, angiographic results, and length of patient follow-up. RESULTS: Our study reports data on 10 patients with a total of 14 fistulae. On follow-up angiography, 8 (57%) had complete occlusion of the fistula with a median time to follow up of 19.5 months. The remaining 6 (43%) were deemed as near-complete occlusion of fistula with a median time to follow up of 12.0 months. Time from radiosurgery to angiogram revealing incomplete vs. angiogram revealing complete obliteration was significantly different (p=0.045). Nearly all AVFs had decreased feeders over time after treatment with only one AVF developing an additional feeder post-treatment. Arterial feeders, drainage site, sex, Borden type, lesion volume and treatment volume had no predictive value of obliteration outcome. CONCLUSIONS: This study provides data on the angioarchitecture of fistulae treated with GKRS and also serves as an extension of previous studies reporting the safety and efficacy of GKRS treatment for DAVF in a specific patient population.

Chronic Kidney Disease and Cognitive Impairment.

Chronic kidney disease (CKD) is associated with a high risk of cognitive impairment (CI). Both vascular and metabolic factors are implicated in the causation of CI in CKD. The traditional risk factors for CI are more prevalent in CKD and interact reciprocally. CI in CKD is associated with reduced functional capacity, poor quality of life and mortality. Cognition declines significantly after initiation of haemodialysis (HD). Repeated cerebral insults related to intra-dialytic haemodynamic instability may be responsible for the rapid, step-wise decline in cognition observed in HD patients. Cognitive interventions used in the general population have not been adequately tested in CKD. Exercise interventions are likely to be beneficial based on biological plausibility and pilot trial data. Cooled HD may be beneficial in HD patients but needs substantive trial data to support it. Cognition testing should be routinely offered to CKD patients. There is a need for further research into the underlying causes of CI in CKD with a view to developing therapeutic interventions.