Basic vascular neuroanatomy of the brain and spine: what the general interventional radiologist needs to know

Sex-specific anatomical variation of circle of Willis arteries

BACKGROUND

Anatomical variations in the circle of Willis (CoW) arteries are common and can affect hemodynamic stress, thereby influencing the risk of cerebrovascular pathology. Previous studies have suggested sex differences in CoW anatomy, but findings vary due to limited study population size and different measurement methods. This study aims to investigate sex differences in artery diameters, anatomical variants and bifurcation angles of the CoW using a large population cohort and semi-automatic measurements.

METHODS

Sex-specific CoW anatomical variations were assessed using Magnetic Resonance Angiography (MRA) scans of 1,052 individuals without intracranial vascular abnormalities. Diameters and bifurcation angles of large CoW arteries (>1.2 mm) were measured with a semi-automatic tool. Diameters of smaller anterior communicating artery (Acom) and posterior communicating arteries (Pcoms) and the anatomical variants of the CoW were determined manually. Generalized Linear Models (GLMs) and logistic regression models with adjustments for covariates were used to compare anatomical variations between sexes.

RESULTS

Men exhibited larger diameters in all semi-automatically measured CoW arteries. A complete anterior CoW was more prevalent in men than women, while there was no difference for the posterior CoW. Aplasia/hypoplasia of the Acom was more prevalent in women. Aplasia/hypoplasia of one Pcom was more common in women, while aplasia/hypoplasia of both Pcoms was more common in men. No sex differences were found in CoW bifurcation angles and in the occurrence of fetal-type posterior cerebral arteries.

CONCLUSION

This study identified significant CoW differences in artery diameters and anatomical variants between sexes, while bifurcation angles between arteries were comparable. Future research should investigate the association between these sex-specific CoW variations and cerebrovascular pathology.

Deep-learning-based detection of large vessel occlusion: A comparison of CT and diffusion-weighted imaging

Background

Rapid and accurate identification of large vessel occlusion (LVO) is crucial for determining eligibility for endovascular treatment. We aimed to validate whether computed tomography combined with clinical information (CT&CI) or diffusion-weighted imaging (DWI) offers better predictive accuracy for anterior circulation LVO.

Methods

Computed tomography combined with clinical information and DWI data from patients diagnosed with acute ischemic stroke were collected. Three deep-learning models, convolutional neural network, EfficientNet-B2, and DenseNet121, were used to compare CT&CI and DWI for detecting anterior circulation LVO.

Results

A total of 456 patients, 228 patients with LVO [68.91 ± 12.84 years, 63.60% male; initial National Institutes of Health Stroke Scale (NIHSS) score: median 11 (7-14)] and without LVO [67.06 ± 12.29 years, 64.04% male; initial NIHSS score: median 2 (1-4)] were enrolled. Diffusion-weighted imaging achieved better results than CT&CI did in each performance metric. In DenseNet121, the area under the curves (AUCs) were found to be 0.833 and 0.756, respectively, while in EfficientNet-B2, the AUCs were 0.815 and 0.647, respectively.

Conclusions

In detecting the presence of anterior circulation LVO, DWI showed better results in each performance metric than CT&CI did, and the best-performing deep-learning model was DenseNet121.

Uncommon Cause, Critical Consequence: Vertebral Artery Aneurysm Resulting in Intraventricular Hemorrhage

The vertebrobasilar system is made up of the two vertebral arteries that unite to form the basilar artery near the base of the skull. Aneurysms in the vertebrobasilar system are distinct from other cerebral aneurysms due to their unique morphologic characteristics. They can be large and bulging (massive), pressing on the brainstem. Alternatively, they might be weak and splitting apart (dissecting) or have an elongated shape (fusiform). On the other end of the spectrum, Vertebral artery aneurysms (VAAs) can also be small and rounded (saccular). These aneurysms can occur at the vertebral artery itself or where it joins the posterior inferior cerebellar artery (PICA). Anatomically, they are situated near the brainstem and cranial nerves, deep within the posterior fossa. The cerebrospinal fluid is kept in transit and flux by the ventricular system's chambers circulating the fluid within themselves. An intraventricular hemorrhage (IVH) can occasionally result from vertebral artery aneurysmal ruptures that result in bleeding into the subarachnoid space and then extravasate into the ventricles. Persistent and poorly controlled hypertension affects about 50% of individuals with IVH. In this case report, we study a 74-year-old woman who complained of a sudden onset headache that had been bothering her for three days at the medical emergency room. She had been diagnosed with systemic hypertension eight years prior and had not taken her medicines as prescribed. She was discovered to have rigidity in her neck and a blood pressure reading of 170/100 mmHg, which had been followed by an episode of vomiting. Radiological investigations revealed a VAA that had a high risk of rupturing and causing an IVH.

The anatomic basis of leptomeningeal metastasis

Leptomeningeal metastasis (LM), or spread of cancer to the cerebrospinal fluid (CSF)-filled space surrounding the central nervous system, is a fatal complication of cancer. Entry into this space poses an anatomical challenge for cancer cells; movement of cells between the blood and CSF is tightly regulated by the blood-CSF barriers. Anatomical understanding of the leptomeninges provides a roadmap of corridors for cancer entry. This Review describes the anatomy of the leptomeninges and routes of cancer spread to the CSF. Granular understanding of LM by route of entry may inform strategies for novel diagnostic and preventive strategies as well as therapies.

Dissecting a radiculomedullary artery as an infrequent cause of low back pain: illustrative case

BACKGROUND

There is currently no case described in the literature of epidural hematoma associated with subarachnoid hemorrhage due to dissection of a spontaneous radiculomedullary artery at the lumbar level and therefore its incidence and prevalence are not known. However, its etiology is thought to be similar and may not be diagnosed given its nonspecific symptomatology.

OBSERVATIONS

The authors present the case of an adult patient who consulted the emergency department for 2 weeks of low back pain. On physical examination there were negative signs of radiculopathy without neurological focalization. The patient was evaluated by neurosurgery via thoracic and lumbosacral spine magnetic resonance imaging, with findings of epidural hematoma associated with subarachnoid hemorrhage in the lumbosacral region. After that, panangiography was done. In the study, it was possible to visualize a dissection of the radicular artery at the L2 level. The patient was not a candidate for surgical management and continued with medical pain management. The patient has a good clinical evolution and was discharged.

LESSONS

The aim of the present case is to describe a unique case of radiculomedullary artery dissection as a cause of spontaneous epidural hematoma associated with a subarachnoid hemorrhage in the lumbar region.

Paving the Road for the Adoption of Normothermic Regional Perfusion in Canada

Donation after circulatory determination of death has increased the number of organs available but can result in worse recipient outcomes than organs recovered from donors after neurologic death. Normothermic regional perfusion is a novel tool that can circumvent the shortcomings of donation after circulatory determination of death. However, its implementation may pose a threat to existing laws surrounding death declaration. Here, we propose a research agenda that will allow this technology to be introduced within current Canadian organ donation frameworks.

Cardiovascular Risk Factors Affect Specific Segments of the Intracranial Vasculature in High-Resolution (HR) Vessel Wall Imaging (VWI)

OBJECTIVES

Luminal-based imaging have identified different risk factors for extracranial and intracranial atherosclerosis (ICAS), but these techniques are known to underestimate the true extent of the disease. High-resolution (HR) vessel wall imaging (VWI) has recently gained recognition as a valuable tool in the assessment of ICAS. The aim of this study is to determine the association between cardiovascular risk factors and specific intracranial vessel segment involvement using HR-VWI.

MATERIALS AND METHODS

From January 2017 to January 2020, consecutive patients ≥ 18 years-old undergoing HR-VWI of the brain were identified. Patients with history of primary or secondary vasculitis, reversible cerebral vasoconstriction syndrome, or moya-moya were excluded. The presence of vessel wall thickening and enhancement were assessed in the perpendicular plane for each vessel segment by two neuroradiologists. Univariate and multivariate analyses were performed to assess associations between imaging findings and cardiovascular risk factors. Interrater reliability was calculated.

RESULTS

Seventy-one patients (39 men; mean age: 55.9 years) were included. Vessel wall enhancement was seen in 39/71 (55%). A total number of 105 vessel segments demonstrated abnormal enhancement and 79/105 (75%) had an eccentric pattern. Eccentric vessel wall enhancement was independently associated with age >65 years-old in the ICA (OR 9.0, CI 2.1 - 38.2, p < 0.01) and proximal MCA (OR 4.0, CI 1.2 - 13.2, p = 0.02), and with hyperlipidemia in the posterior circulation (OR 44.0, CI2.9-661.0, p<0.01).

CONCLUSION

There is a significant association between eccentric vessel wall enhancement of the ICA and proximal MCA in patients with age > 65; and of the proximal posterior circulation (basilar - PCA1) with hyperlipidemia.

Cumulative Damage: Cell Death in Posthemorrhagic Hydrocephalus of Prematurity

Globally, approximately 11% of all infants are born preterm, prior to 37 weeks’ gestation. In these high-risk neonates, encephalopathy of prematurity (EoP) is a major cause of both morbidity and mortality, especially for neonates who are born very preterm (<32 weeks gestation). EoP encompasses numerous types of preterm birth-related brain abnormalities and injuries, and can culminate in a diverse array of neurodevelopmental impairments. Of note, posthemorrhagic hydrocephalus of prematurity (PHHP) can be conceptualized as a severe manifestation of EoP. PHHP impacts the immature neonatal brain at a crucial timepoint during neurodevelopment, and can result in permanent, detrimental consequences to not only cerebrospinal fluid (CSF) dynamics, but also to white and gray matter development. In this review, the relevant literature related to the diverse mechanisms of cell death in the setting of PHHP will be thoroughly discussed. Loss of the epithelial cells of the choroid plexus, ependymal cells and their motile cilia, and cellular structures within the glymphatic system are of particular interest. Greater insights into the injuries, initiating targets, and downstream signaling pathways involved in excess cell death shed light on promising areas for therapeutic intervention. This will bolster current efforts to prevent, mitigate, and reverse the consequential brain remodeling that occurs as a result of hydrocephalus and other components of EoP.

Brachiocephalic and subclavian stenosis: Current concepts for cardiovascular specialists

Brachiocephalic and subclavian artery stenoses are less common manifestations of peripheral arterial disease (PAD) compared to lower extremity PAD. However, even among asymptomatic patients, a diagnosis of PAD portends worse long-term mortality. Symptoms may include subclavian steal syndrome and arm claudication. Among patients with internal mammary coronary bypass grafts, symptoms may include those of myocardial ischemia. Symptomatic subclavian stenosis can be readily treated using endovascular techniques with durable outcomes.

The circle of Willis revisited: Forebrain dehydration sensing facilitated by the anterior communicating artery: How hemodynamic properties facilitate more efficient dehydration sensing in amniotes

We hypothesize that threat of dehydration provided selection pressure for the evolutionary emergence and persistence of the anterior communicating artery (ACoA - the inter-arterial connection that completes the Circle of Willis) in early amniotes. The ACoA is a hemodynamically insignificant artery, but, as we argue in this paper, its privileged position outside the blood-brain barrier gives it a crucial sensing function for the osmolarity of the blood against the background of the rest of the brain, which efficiently protects itself from dehydration. Till now, the questions of why the ACoA evolved, and what its physiological function is, have remained unsatisfactorily answered. The traditional view-that the ACoA serves as a collateral source of vascularization in case of arterial stenosis-is anthropocentric, and not in accordance with principles of natural selection that apply more generally. Diseases underlying arterial stenosis are associated with aging and the human lifestyle, so this cannot explain why the ACoA formed hundreds of millions of years ago and persisted in amniotes to this day. The peculiar hemodynamic properties of the ACoA could be selected traits that allowed for more efficient forebrain detection of dehydration and complex behavioral responses to water loss, a major advantage in the survival of early amniotes. This hypothesis also explains insufficient hydration often seen in elderly humans.

Maintaining the permanence principle for death during in situ normothermic regional perfusion for donation after circulatory death organ recovery: A United Kingdom and Canadian proposal

There is international variability in the determination of death. Death in donation after circulatory death (DCD) can be defined by the permanent cessation of brain circulation. Post-mortem interventions that restore brain perfusion should be prohibited as they invalidate the diagnosis of death. Retrieval teams should develop protocols that ensure the continued absence of brain perfusion during DCD organ recovery. In situ normothermic regional perfusion (NRP) or restarting the heart in the donor's body may interrupt the permanent cessation of brain perfusion because, theoretically, collateral circulations may restore it. We propose refinements to current protocols to monitor and exclude brain reperfusion during in situ NRP. In abdominal NRP, complete occlusion of the descending aorta prevents brain perfusion in most cases. Inserting a cannula in the ascending aorta identifies inadequate occlusion of the descending aorta or any collateral flow and diverts flow away from the brain. In thoracoabdominal NRP opening the aortic arch vessels to atmosphere allows collateral flow to be diverted away from the brain, maintaining the permanence standard for death and respecting the dead donor rule. We propose that these hypotheses are correct when using techniques that simultaneously occlude the descending aorta and open the aortic arch vessels to atmosphere.

Posthemorrhagic hydrocephalus development after germinal matrix hemorrhage: Established mechanisms and proposed pathways

In addition to being the leading cause of morbidity and mortality in premature infants, germinal matrix hemorrhage (GMH) is also the leading cause of acquired infantile hydrocephalus. The pathophysiology of posthemorrhagic hydrocephalus (PHH) development after GMH is complex and vaguely understood, although evidence suggests fibrosis and gliosis in the periventricular and subarachnoid spaces disrupts normal cerebrospinal fluid (CSF) dynamics. Theories explaining general hydrocephalus etiology have substantially evolved from the original bulk flow theory developed by Dr. Dandy over a century ago. Current clinical and experimental evidence supports a new hydrodynamic theory for hydrocephalus development involving redistribution of vascular pulsations and disruption of Starling forces in the brain microcirculation. In this review, we discuss CSF flow dynamics, history and development of theoretical hydrocephalus pathophysiology, and GMH epidemiology and etiology as it relates to PHH development. We highlight known mechanisms and propose new avenues that will further elucidate GMH pathophysiology, specifically related to hydrocephalus.

Bioprinting of freestanding vascular grafts and the regulatory considerations for additively manufactured vascular prostheses

Vasculature is the network of blood vessels of an organ or body part that allow for the exchange of nutrients and waste to and from every cell, thus establishing a circulatory equilibrium. Vascular health is at risk from a variety of conditions that includes disease and trauma. In some cases, medical therapy can alleviate the impacts of the condition. Intervention is needed in other instances to restore the health of abnormal vasculature. The main approaches to treat vascular conditions are endovascular procedures and open vascular reconstruction that often requires a graft to accomplish. However, current vascular prostheses have limitations that include size mismatch with the native vessel, risk of immunogenicity from allografts and xenografts, and unavailability of autografts. In this review, we discuss efforts in bioprinting, an emerging method for vascular reconstruction. This includes an overview of 3D printing processes and materials, graft characterization strategies and the regulatory aspects to consider for the commercialization of 3D bioprinted vascular prostheses.

Magnetic resonance angiography determined variations in the circle of Willis: Analysis of a large series from a single center

OBJECTIVE

The purpose of this study is to evaluate and describe the prevalence and patterns of arterial variants in the circle of Willis (CW) seen in noncontrast three-dimensional time-of-flight magnetic resonance angiography in a series of patients with cerebral vascular accidents (CVAs).

MATERIALS AND METHODS

A descriptive study was undertaken in 200 patients who presented for screening for CVA in the Department of Radiodiagnosis and Imaging, St. John's Medical College Hospital, Bengaluru, from September 2014 to September 2016.

RESULTS

The most common types of CW in a single subject were anterior variant Type A and posterior variant Type E. Type A in the anterior circulation is the normal adult pattern. There is a single anterior communicating artery. The internal carotid artery bifurcates into the precommunicating segment of the anterior cerebral artery and middle cerebral artery. Type E in the posterior circulation is hypoplasia or absence of both posterior communicating arteries and isolation of the anterior and posterior parts of the circle at this level. Overall, CW variants were slightly more common in women than in men.

CONCLUSION

Our findings show that the configuration of the CW may vary greatly in the general population. The wide range in the morphology of CW warrants further research on various races and larger populations to confirm the influence of genetic, regional, environmental, and hemodynamic factors or their combination.

Stroke Longitudinal Volumetric Measures Correlate with the Behavioral Score in Non-Human Primates

Stroke is the second leading cause of death worldwide. Brain imaging data from experimental rodent stroke models suggest that size and location of the ischemic lesion relate to behavioral outcome. However, such a relationship between these two variables has not been established in Non-Human Primate (NHP) models. Thus, we aimed to evaluate whether size, location, and severity of stroke following controlled Middle Cerebral Artery Occlusion (MCAO) in NHP model correlated to neurological outcome. Forty cynomolgus macaques underwent MCAO, after four mortalities, thirty-six subjects were followed up during the longitudinal study. Structural T2 scans were obtained by magnetic resonance imaging (MRI) prior to, 48 h, and 30 days post-MCAO. Neurological function was assessed with the Non-human Primate Stroke Scale (NHPSS). T2 whole lesion volume was calculated per subject. At chronic stages, remaining brain volume was computed, and the affected hemisphere parceled into 50 regions of interest (ROIs). Whole and parceled volumetric measures were analyzed in relation to the NHPSS score. The longitudinal lesion volume evaluation showed a positive correlation with the NHPSS score, whereas the remaining brain volume negatively correlated with the NHPSS. Following ROI parcellation, NHPSS outcome correlated with frontal, temporal, occipital, and middle white matter, as well as the internal capsule, and the superior temporal and middle temporal gyri, and the caudate nucleus. These results represent an important step in stroke translational research by demonstrating close similarities between the NHP stroke model and the clinical characteristics following a human stroke and illustrating significant areas that could represent targets for novel neuroprotective strategies.

Toward dynamic lumbar puncture guidance using needle-based single-element ultrasound imaging

Lumbar punctures (LPs) are interventional procedures that are used to collect cerebrospinal fluid. Since the target window is small, physicians have limited success conducting the procedure. The procedure is especially difficult for obese patients due to the increased distance between bone and skin surface. We propose a simple and direct needle insertion platform, enabling image formation by sweeping a needle with a single ultrasound element at the tip. The needle-shaped ultrasound transducer can not only sense the distance between the tip and a potential obstacle, such as bone, but also visually locate the structures by combining transducer location tracking and synthetic aperture focusing. The concept of the system was validated through a simulation that revealed robust image reconstruction under expected errors in tip localization. The initial prototype was built into a 14 G needle and was mounted on a holster equipped with a rotation shaft allowing one degree-of-freedom rotational sweeping and a rotation tracking encoder. We experimentally evaluated the system using a metal-wire phantom mimicking high reflection bone structures and human spinal bone phantom. Images of the phantoms were reconstructed, and the synthetic aperture reconstruction improved the image quality. These results demonstrate the potential of the system to be used as a real-time guidance tool for improving LPs.

The Paravascular Pathway for Brain Waste Clearance: Current Understanding, Significance and Controversy

The paravascular pathway, also known as the “glymphatic” pathway, is a recently described system for waste clearance in the brain. According to this model, cerebrospinal fluid (CSF) enters the paravascular spaces surrounding penetrating arteries of the brain, mixes with interstitial fluid (ISF) and solutes in the parenchyma, and exits along paravascular spaces of draining veins. Studies have shown that metabolic waste products and solutes, including proteins involved in the pathogenesis of neurodegenerative diseases such as amyloid-beta, may be cleared by this pathway. Consequently, a growing body of research has begun to explore the association between glymphatic dysfunction and various disease states. However, significant controversy exists in the literature regarding both the direction of waste clearance as well as the anatomical space in which the waste-fluid mixture is contained. Some studies have found no evidence of interstitial solute clearance along the paravascular space of veins. Rather, they demonstrate a perivascular pathway in which waste is cleared from the brain along an anatomically distinct perivascular space in a direction opposite to that of paravascular flow. Although possible explanations have been offered, none have been able to fully reconcile the discrepancies in the literature, and many questions remain. Given the therapeutic potential that a comprehensive understanding of brain waste clearance pathways might offer, further research and clarification is highly warranted.

Arterial Blood Supply to the Spinal Cord in Animal Models of Spinal Cord Injury. A Review

Animal models are used to examine the results of experimental spinal cord injury. Alterations in spinal cord blood supply caused by complex spinal cord injuries contribute significantly to the diversity and severity of the spinal cord damage, particularly ischemic changes. However, the literature has not completely clarified our knowledge of anatomy of the complex three-dimensional arterial system of the spinal cord in experimental animals, which can impede the translation of experimental results to human clinical applications. As the literary sources dealing with the spinal cord arterial blood supply in experimental animals are limited and scattered, the authors performed a review of the anatomy of the arterial blood supply to the spinal cord in several experimental animals, including pigs, dogs, cats, rabbits, guinea pigs, rats, and mice and created a coherent format discussing the interspecies differences. This provides researchers with a valuable tool for the selection of the most suitable animal model for their experiments in the study of spinal cord ischemia and provides clinicians with a basis for the appropriate translation of research work to their clinical applications. Anat Rec, 300:2091-2106, 2017. © 2017 Wiley Periodicals, Inc.

Predictors of Adamkiewicz artery and anterior spinal artery detection through computerized tomographic angiography

Background:

The detection of the Adamkiewicz artery and the anterior spinal artery has been associated with the ability to prevent adverse spinal cord outcomes after aortic surgical procedures. Yet, to our knowledge, no previous studies have attempted to use modern predictive models to identify the most important variables in determining artery detectability.

Aims:

To develop a model to predict the odds of visualizing the Adamkiewicz artery or anterior spinal artery in patients undergoing computerized tomographic angiography.

Methods:

We conducted a prospective, cross-sectional study. Outcomes of interest were the non-detection of the Adamkiewicz artery and anterior spinal artery, and their corresponding level of origin. Axial images were inspected in high definition in search of two dense spots characterizing the Adamkiewicz artery and anterior spinal artery. A multiplanar three-dimensional reconstruction was then performed using the OsiriX® software.

Results:

A total of 110 participants were part of this analysis. When evaluating risks for the Adamkiewicz artery being undetectable, significant factors could be classified into three broad categories: risk factors for arterial disease, established arterial disease, and obesity. Factors in the former category included metabolic syndrome, hypertension, and smoking status, while factors in the arterial disease included descending aortic aneurysm, mural thrombi, aortic aneurysm without a dissection, and aortic disease in general. In relation to anterior spinal artery not being detectable, significant risk factors included hypertension, smoking status, and metabolic syndrome, while those associated with arterial disease involved aortic disease and arterial thrombi. When evaluating the importance of individual clinical factors, the presence of higher body mass index was the single most important risk factor.

Conclusion:

Arterial disease, established arterial disease, and increased body mass index are risk factors in the detection of Adamkiewicz artery and anterior spinal artery. Specific diagnostic protocols should be in place for patients with these underlying conditions, thus enhancing the likelihood of detection when the Adamkiewicz artery is indeed present.

The Glymphatic System: A Beginner's Guide

The glymphatic system is a recently discovered macroscopic waste clearance system that utilizes a unique system of perivascular tunnels, formed by astroglial cells, to promote efficient elimination of soluble proteins and metabolites from the central nervous system. Besides waste elimination, the glymphatic system also facilitates  brain-wide distribution of several compounds, including glucose, lipids, amino acids, growth factors, and neuromodulators. Intriguingly, the glymphatic system function mainly during sleep and is largely disengaged during wakefulness. The biological need for sleep across all species may therefore reflect that the brain must enter a state of activity that enables elimination of potentially neurotoxic waste products, including β-amyloid. Since the concept of the glymphatic system is relatively new, we will here review its basic structural elements, organization, regulation, and functions. We will also discuss recent studies indicating that glymphatic function is suppressed in various diseases and that failure of glymphatic function in turn might contribute to pathology in neurodegenerative disorders, traumatic brain injury and stroke.

Interventional management of vertebral body metastases

Metastases to the vertebral column are often due to hypervascular primary tumors, the most common of which is renal cell carcinoma. Clinical symptoms attributed to vertebral body metastases include localized pain, mechanical instability of the vertebral column, and neurologic deficits resulting from mass effect. Treatment options include targeted radiotherapy, percutaneous vertebral augmentation with or without thermal ablation, and surgical resection with subsequent fusion. Overall, surgical resection of the tumor and stabilization of the vertebral column provide the best prognosis for the patient in terms of symptomatic improvement and long-term survival; however, resection of hypervascular vertebral body metastases can result in significant intraoperative blood loss that can add to the morbidity of the procedure. Preoperative embolization of hypervascular metastases of the vertebral column has been shown to significantly reduce intraoperative blood loss at the time of surgery. The goal of this manuscript is to describe the role of embolization therapy in the management of patients with vertebral body metastases.