Differential gene expression in human cerebrovascular malformations

Histopathological analysis of the wall enhancement of the spinal dural arteriovenous fistulae's draining veins

OBJECTIVE

The mechanism behind SDAVF is still unclear. We discovered that the vessel wall of the SDAVF-DV occasionally showed enhancement in MRI, and this study assessed the relationship between the enhancement of the draining vein's wall and its histology.

METHODS

For histopathologic analysis, 16 draining vein samples from 16 patients with SDAVF were included, 3 normal arteries and 3 normal veins were chosen as comparison. We assessed the imaging and microscopic characteristics of the draining veins in SDAVF patients. The former included the presence of significant enhancement of the wall of the draining vein in MRI, and the latter included the adherence, aggregation, infiltration of pro-inflammatory factors and inflammatory cells. Immuno-histochemical staining was performed using IL-1β, IL-8, TGF-β as well as MPO and MMP-9, and positive results were counted. Multiple logistic regression analysis was used to determine whether the infiltration of inflammatory cells was connected to vessel wall enhancement in the SDAVF-DV.

RESULTS

Infiltration of inflammatory cells was significantly higher in SDAVF-DV compared to normal vessels, 7 out of 16 patients significantly had enhancement of the vessel wall of SDAVF-DV, and logistic regression analysis showed that samples with more infiltration of inflammatory cells were more likely to show enhancement of the SDAVF-DV walls.

CONCLUSION

There was considerable inflammatory cells infiltration in SDAVF-DV, and this may explain why their vessel wall had such a significant enhancement in MRI.

The Role and Therapeutic Implications of Inflammation in the Pathogenesis of Brain Arteriovenous Malformations

Brain arteriovenous malformations (bAVMs) are focal vascular lesions composed of abnormal vascular channels without an intervening capillary network. As a result, high-pressure arterial blood shunts directly into the venous outflow system. These high-flow, low-resistance shunts are composed of dilated, tortuous, and fragile vessels, which are prone to rupture. BAVMs are a leading cause of hemorrhagic stroke in children and young adults. Current treatments for bAVMs are limited to surgery, embolization, and radiosurgery, although even these options are not viable for ~20% of AVM patients due to excessive risk. Critically, inflammation has been suggested to contribute to lesion progression. Here we summarize the current literature discussing the role of the immune system in bAVM pathogenesis and lesion progression, as well as the potential for targeting inflammation to prevent bAVM rupture and intracranial hemorrhage. We conclude by proposing that a dysfunctional endothelium, which harbors the somatic mutations that have been shown to give rise to sporadic bAVMs, may drive disease development and progression by altering the immune status of the brain.

Molecular and genetic mechanisms in brain arteriovenous malformations: new insights and future perspectives

Brain arteriovenous malformations (bAVMs) are rare vascular lesions made of shunts between cerebral arteries and veins without the interposition of a capillary bed. The majority of bAVMs are asymptomatic, but some may be revealed by seizures and potentially life-threatening brain hemorrhage. The management of unruptured bAVMs remains a matter of debate. Significant progress in the understanding of their pathogenesis has been made during the last decade, particularly using genome sequencing and biomolecular analysis. Herein, we comprehensively review the recent molecular and genetic advances in the study of bAVMs that not only allow a better understanding of the genesis and growth of bAVMs, but also open new insights in medical treatment perspectives.

Cerebral Cavernous Malformation: Immune and Inflammatory Perspectives

Cerebral cavernous malformation (CCM) is a type of vascular anomaly that arises due to the dyshomeostasis of brain capillary networks. In the past two decades, many advances have been made in this research field. Notably, as a more reasonable current view, the CCM lesions should be attributed to the results of a great number of additional events related to the homeostasis disorder of the endothelial cell. Indeed, one of the most fascinating concerns in the research field is the inflammatory perturbation in the immune microenvironment, which would affect the disease progression as well as the patients’ outcomes. In this work, we focused on this topic, and underlined the immune-related factors’ contribution to the CCM pathologic progression.

Review of treatment and therapeutic targets in brain arteriovenous malformation

Brain arteriovenous malformations (bAVM) are an important cause of intracranial hemorrhage (ICH), especially in younger patients. The pathogenesis of bAVM are largely unknown. Current understanding of bAVM etiology is based on studying genetic syndromes, animal models, and surgically resected specimens from patients. The identification of activating somatic mutations in the Kirsten rat sarcoma viral oncogene homologue (KRAS) gene and other mitogen-activated protein kinase (MAPK) pathway genes has opened up new avenues for bAVM study, leading to a paradigm shift to search for somatic, de novo mutations in sporadic bAVMs instead of focusing on inherited genetic mutations. Through the development of new models and understanding of pathways involved in maintaining normal vascular structure and functions, promising therapeutic targets have been identified and safety and efficacy studies are underway in animal models and in patients. The goal of this paper is to provide a thorough review or current diagnostic and treatment tools, known genes and key pathways involved in bAVM pathogenesis to summarize current treatment options and potential therapeutic targets uncovered by recent discoveries.

The role of mural cells in hemorrhage of brain arteriovenous malformation

Brain arteriovenous malformation (bAVM) is the most common cause of intracranial hemorrhage (ICH), particularly in young patients. However, the exact cause of bAVM bleeding and rupture is not yet fully understood. In bAVMs, blood bypasses the entire capillary bed and directly flows from arteries to veins. The vessel walls in bAVMs have structural defects, which impair vascular integrity. Mural cells are essential structural and functional components of blood vessels and play a critical role in maintaining vascular integrity. Changes in mural cell number and coverage have been implicated in bAVMs. In this review, we discussed the roles of mural cells in bAVM pathogenesis. We focused on 1) the recent advances in human and animal studies of bAVMs; 2) the importance of mural cells in vascular integrity; 3) the regulatory signaling pathways that regulate mural cell function. More specifically, the platelet-derived growth factor-B (PDGF-B)/PDGF receptor-β (PDGFR-β), EphrinB2/EphB4, and angiopoietins/tie2 signaling pathways that regulate mural cell-recruitment during vascular remodeling were discussed in detail.

Cerebrovascular Anomalies: Perspectives From Immunology and Cerebrospinal Fluid Flow

Appropriate vascular function is essential for the maintenance of central nervous system homeostasis and is achieved through virtue of the blood-brain barrier; a specialized structure consisting of endothelial, mural, and astrocytic interactions. While appropriate blood-brain barrier function is typically achieved, the central nervous system vasculature is not infallible and cerebrovascular anomalies, a collective terminology for diverse vascular lesions, are present in meningeal and cerebral vasculature supplying and draining the brain. These conditions, including aneurysmal formation and rupture, arteriovenous malformations, dural arteriovenous fistulas, and cerebral cavernous malformations, and their associated neurological sequelae, are typically managed with neurosurgical or pharmacological approaches. However, increasing evidence implicates interacting roles for inflammatory responses and disrupted central nervous system fluid flow with respect to vascular perturbations. Here, we discuss cerebrovascular anomalies from an immunologic angle and fluid flow perspective. We describe immune contributions, both common and distinct, to the formation and progression of diverse cerebrovascular anomalies. Next, we summarize how cerebrovascular anomalies precipitate diverse neurological sequelae, including seizures, hydrocephalus, and cognitive effects and possible contributions through the recently identified lymphatic and glymphatic systems. Finally, we speculate on and provide testable hypotheses for novel nonsurgical therapeutic approaches for alleviating neurological impairments arising from cerebrovascular anomalies, with a particular emphasis on the normalization of fluid flow and alleviation of inflammation through manipulations of the lymphatic and glymphatic central nervous system clearance pathways.

RNF213 rare variants and cerebral arteriovenous malformation in a Chinese population

OBJECTIVE

Cerebral arteriovenous malformation (AVM) is characterised by an abnormal tangle of arteries and veins, the rupture of which is a significant portion of the morbidity and mortality cases, especially in young populations. However, the exact risk factors and pathophysiologic mechanisms of AVM remain poorly understood. RNF213 variants have been identified as obvious susceptible factors of several cerebrovascular disorders, such as Moyamoya disease and intracranial aneurysms. Thus, this study aimed to determine whether there is an association between RNF213 rare variants and AVM.

METHODS

The AVM group included 22 patients with AVM. The control group included 1007 samples from the GeneSky in-house database and 208 samples from the 1000 Genome Project of Chinese Han Population. Genomic DNA samples were extracted from the peripheral blood of the AVM patients, and targeted exome sequencing of RNF213 was performed to assess the existence of low-frequency or rare variants. Sanger sequencing was performed to validate the identified variants. Logistic regression analysis was performed to calculate the odds ratios (ORs) and 95 % confidence intervals (CIs) of the candidate variants and risk of AVM. Statistical analyses were performed using SPSS version 21.0.

RESULTS

The RNF213 c.10997T>C variant (amino acid mutation p.M3666T, NM_001256071) was observed in two AVM patients after filtration. It was significantly associated with AVM in the Chinese population (ORs, 10.30 and 25.08; 95 %; CIs, 1.38-77.10 and 4.34-144.90 compared with 1000 Genome Project of Chinese Han Population and GeneSky in-house database, respectively).

CONCLUSION

Rare variants of RNF213 are associated with AVM in the Chinese population, suggesting the important role of RNF213 in AVM. Further studies are needed to verify these findings.

Neurovascular inflammation in the pathogenesis of brain arteriovenous malformations

Brain arteriovenous malformations (bAVM) arise as congenital or sporadic focal lesions with a significant risk for intracerebral hemorrhage (ICH). A wide range of interindividual differences is present in the onset, progression, and severity of bAVM. A growing body of gene expression and polymorphism-based research studies support the involvement of localized inflammation in bAVM disease progression and rupture. In this review article, we analyze the altered responses of neural, vascular, and immune cell types that contribute to the inflammatory process, which exacerbates the pathophysiological progression of vascular dysmorphogenesis in bAVM lesions. The cumulative effect of inflammation in bAVM development is orchestrated by various genetic moderators and inflammatory mediators. We also discuss the potential therapies for the treatment of brain AVM by targeting the inflammatory processes and mediators. Elucidating the precise role of inflammation in the bAVM growth and hemorrhage would open novel avenues for noninvasive and effectual causal therapy that may complement the current therapeutic strategies.

Single Cell Analysis in Vascular Biology

The ability to quantify DNA, RNA, and protein variations at the single cell level has revolutionized our understanding of cellular heterogeneity within tissues. Via such analyses, individual cells within populations previously thought to be homogeneous can now be delineated into specific subpopulations expressing unique sets of genes, enabling specialized functions. In vascular biology, studies using single cell RNA sequencing have revealed extensive heterogeneity among endothelial and mural cells even within the same vessel, key intermediate cell types that arise during blood and lymphatic vessel development, and cell-type specific responses to disease. Thus, emerging new single cell analysis techniques are enabling vascular biologists to elucidate mechanisms of vascular development, homeostasis, and disease that were previously not possible. In this review, we will provide an overview of single cell analysis methods and highlight recent advances in vascular biology made possible through single cell RNA sequencing.

RNA-Sequencing Highlights Inflammation and Impaired Integrity of the Vascular Wall in Brain Arteriovenous Malformations

Background and Purpose—

Interventional treatment of unruptured brain arteriovenous malformations (BAVMs) has become increasingly controversial. Because medical therapy is still lacking, we aimed to obtain insight into the disease mechanisms implicated in BAVMs and to identify potential targets for medical treatment to prevent rupture of a BAVM.

Methods—

We used next-generation RNA sequencing to identify differential expression on a transcriptome-wide level comparing tissue samples of 12 BAVMs to 16 intracranial control arteries. We identified differentially expressed genes by negative binominal generalized log-linear regression (false discovery rate corrected P <0.05). We selected 10 genes for validation using droplet digital polymerase chain reaction. We performed functional pathway analysis accounting for potential gene-length bias, to establish enhancement of biological pathways involved in BAVMs. We further assessed which Gene Ontology terms were enriched.

Results—

We found 736 upregulated genes in BAVMs including genes implicated in the cytoskeletal machinery and cell-migration and genes encoding for inflammatory cytokines and secretory products of neutrophils and macrophages. Furthermore, we found 498 genes downregulated including genes implicated in extracellular matrix composition, the binary angiopoietin-TIE system, and TGF (transforming growth factor)-β signaling. We confirmed the differential expression of top 10 ranked genes. Functional pathway analysis showed enrichment of the protein digestion and absorption pathway (false discovery rate-adjusted P =1.70×10 −2 ). We identified 47 enriched Gene Ontology terms (false discovery rate-adjusted P <0.05) implicated in cytoskeleton network, cell-migration, endoplasmic reticulum, transmembrane transport, and extracellular matrix composition.

Conclusions—

Our genome-wide RNA-sequencing study points to involvement of inflammatory mediators, loss of cerebrovascular quiescence, and impaired integrity of the vascular wall in the pathophysiology of BAVMs. Our study may lend support to potential receptivity of BAVMs to medical therapeutics, including those promoting vessel maturation, and anti-inflammatory and immune-modifying drugs.

Defective vascular signaling & prospective therapeutic targets in brain arteriovenous malformations

The neurovascular unit is composed of endothelial cells, vascular smooth muscle cells, pericytes, astrocytes and neurons. Through tightly regulated multi-directional cell signaling, the neurovascular unit is responsible for the numerous functionalities of the cerebrovasculature - including the regulation of molecular and cellular transport across the blood-brain barrier, angiogenesis, blood flow responses to brain activation and neuroinflammation. Historically, the study of the brain vasculature focused on endothelial cells; however, recent work has demonstrated that pericytes and vascular smooth muscle cells - collectively known as mural cells - play critical roles in many of these functions. Given this emerging data, a more complete mechanistic understanding of the cellular basis of brain vascular malformations is needed. In this review, we examine the integrated functions and signaling within the neurovascular unit necessary for normal cerebrovascular structure and function. We then describe the role of aberrant cell signaling within the neurovascular unit in brain arteriovenous malformations and identify how these pathways may be targeted therapeutically to eradicate or stabilize these lesions.

Comprehensive transcriptome analysis of cerebral cavernous malformation across multiple species and genotypes

The purpose of this study was to determine important genes, functions, and networks contributing to the pathobiology of cerebral cavernous malformation (CCM) from transcriptomic analyses across 3 species and 2 disease genotypes. Sequencing of RNA from laser microdissected neurovascular units of 5 human surgically resected CCM lesions, mouse brain microvascular endothelial cells, Caenorhabditis elegans with induced Ccm gene loss, and their respective controls provided differentially expressed genes (DEGs). DEGs from mouse and C. elegans were annotated into human homologous genes. Cross-comparisons of DEGs between species and genotypes, as well as network and gene ontology (GO) enrichment analyses, were performed. Among hundreds of DEGs identified in each model, common genes and 1 GO term (GO:0051656, establishment of organelle localization) were commonly identified across the different species and genotypes. In addition, 24 GO functions were present in 4 of 5 models and were related to cell-to-cell adhesion, neutrophil-mediated immunity, ion transmembrane transporter activity, and responses to oxidative stress. We have provided a comprehensive transcriptome library of CCM disease across species and for the first time to our knowledge in Ccm1/Krit1 versus Ccm3/Pdcd10 genotypes. We have provided examples of how results can be used in hypothesis generation or mechanistic confirmatory studies.

LncRNAs expression signatures of human brain arteriovenous malformation revealed by microarray

Long noncoding RNAs (LncRNAs) were important genes involved in a variety of biological functions. They are aberrantly expressed in many types of diseases. In this study, we described LncRNAs profiles in 4 pairs of human brain arteriovenous malformation(AVM) and the corresponding fragment of superior temporal arteries(STA) or small scalp arteries (controlled arteries, CA) and try to find LncRNAs that correlated with the human brain AVM and with clinical symptoms.4 pairs of AVM tissues and corresponding STA or scalp artery fragments (depended on the operative approach) of 4 AVM patients who were admitted in Beijing TianTan hospital were collected. Then LncRNA and mRNA expression profiling analysis was performed by Arraystar-LncRNA array. From the data, we found 1931 LncRNAs upregulated (>2 folds) and 1852 downregulated (<2 folds) in total 28,012 LncRNAs that could be detected. We also found 1577 upregulated mRNAs (>2 folds) and 1699 downregulated (<2 folds) in 21,780 mRNAs that could be detected. LncRNAs (ENST00000423394, ENST00000444114, TCONS_00013855, and ENST00000452148) were evaluated by qPCR in 14 pairs of AVM nidus and the control. This 4 LncRNAs were aberrantly expressed in AVM nidus compared with the control. LncRNA (ENST00000423394) correlated with epilepsy (R = 0.34, P = .02, 95% confidence interval 0.08-0.85)We found that development of AVM may correspond with downregulation of NADPH reductase, lipoprotein lipase and Optic atrophy related proteins. It also may correspond with upregulation of Fcγreceptor. The downregulation of NADPH reductase may correlate with seizures of AVM patients.

In vivo imaging of endothelial cell adhesion molecule expression after radiosurgery in an animal model of arteriovenous malformation

Focussed radiosurgery may provide a means of inducing molecular changes on the luminal surface of diseased endothelium to allow targeted delivery of novel therapeutic compounds. We investigated the potential of ionizing radiation to induce surface expression of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) on endothelial cells (EC) in vitro and in vivo, to assess their suitability as vascular targets in irradiated arteriovenous malformations (AVMs). Cultured brain microvascular EC were irradiated by linear accelerator at single doses of 0, 5, 15 or 25 Gy and expression of ICAM-1 and VCAM-1 measured by qRT-PCR, Western, ELISA and immunocytochemistry. In vivo, near-infrared (NIR) fluorescence optical imaging using Xenolight 750-conjugated ICAM-1 or VCAM-1 antibodies examined luminal biodistribution over 84 days in a rat AVM model after Gamma Knife surgery at a single 15 Gy dose. ICAM-1 and VCAM-1 were minimally expressed on untreated EC in vitro. Doses of 15 and 25 Gy stimulated expression equally; 5 Gy was not different from the unirradiated. In vivo, normal vessels did not bind or retain the fluorescent probes, however binding was significant in AVM vessels. No additive increases in probe binding were found in response to radiosurgery at a dose of 15 Gy. In summary, radiation induces adhesion molecule expression in vitro but elevated baseline levels in AVM vessels precludes further induction in vivo. These molecules may be suitable targets in irradiated vessels without hemodynamic derangement, but not AVMs. These findings demonstrate the importance of using flow-modulated, pre-clinical animal models for validating candidate proteins for vascular targeting in irradiated AVMs.

Neurovascular patterning cues and implications for central and peripheral neurological disease

The highly branched nervous and vascular systems run along parallel trajectories throughout the human body. This stereotyped pattern of branching shared by the nervous and vascular systems stems from a common reliance on specific cues critical to both neurogenesis and angiogenesis. Continually emerging evidence supports the notion of later-evolving vascular networks co-opting neural molecular mechanisms to ensure close proximity and adequate delivery of oxygen and nutrients to nervous tissue. As our understanding of these biologic pathways and their phenotypic manifestations continues to advance, identification of where pathways go awry will provide critical insight into central and peripheral nervous system pathology.

The relationship of cortical folding and brain arteriovenous malformations

Background

The pathogenesis of human intracranial arteriovenous malformations (AVMs) is not well understood; this study aims to quantitatively assess cortical folding in patients with these lesions.

Methods

Seven adult participants, 4 male and 3 female, with unruptured, surgically unresectable intracranial AVMs were prospectively enrolled in the study, with a mean age of 42.1 years and Spetzler-Martin grade range of II–IV. High-resolution brain MRI T1 and T2 sequences were obtained. After standard preprocessing, segmentation and registration techniques, three measures of cortical folding, the depth difference index (DDI), coordinate distance index (CDI) and gyrification index (GI)), were calculated for the affected and unaffected hemispheres of each subject as well as a healthy control subject set.

Results

Of the three metrics, CDI, DDI and GI, used for cortical folding assessment, none demonstrated significant differences between the participants and previously studied healthy adults. There was a significant negative correlation between the DDI ratio between affected and unaffected hemispheres and AVM volume (correlation coefficient r = −0.74, p = 0.04).

Conclusion

This study is the first to quantitatively assess human brain cortical folding in the presence of intracranial AVMs and no significant differences between AVM-affected versus unaffected hemispheres were found in a small dataset. We suggest longitudinal, larger human MRI-based cortical folding studies to assess whether AVMs are congenital lesions of vascular development or de novo, dynamic lesions.

Increased expression of angiogenic factors in cultured human brain arteriovenous malformation endothelial cells

To compare the mRNA level of angiogenic factor vascular endothelial growth factor (VEGF), matrix metalloproteinases (MMP)-2, and MMP-9 in cultured human brain arteriovenous malformation (AVM) endothelial cells (ECs) and normal brain endothelial cells (BECs). Tissue explants both from deformed vessels of AVM and normal microvessel were put into culture for endothelial cells. After the monolayer adherent ECs reached confluence, they were tested with endothelial specific marker CD34 and von Willebrand factor (vWF) by immunochemical assay. mRNA levels of VEGF-A, MMP-2, and MMP-9 in AVM endothelial cells (AVMECs) and BECs were measured by PCR. Immunostaining confirmed that more than 95 % of the cultured cells were CD34 (Fig. 1b) and/or vWF positive. Expression levels of VEGF-A and MMP-2 mRNAs were significantly higher in AVMECs than in BECs. The MMP-9 level was also increased in AVMECs, but the difference was not statistically significant. Vascular tissue explants adherent method is a better approach for isolation and culture of AVMECs. Cultured AVMECs expressed higher angiogenic factors (VEGF, MMP-2) than the controlled BECs, implicating angiogenesis plays an important role in the pathogenesis of AVM.

The role of SDF-1/CXCR4 in the vasculogenesis and remodeling of cerebral arteriovenous malformation

Background

Cerebral arteriovenous malformation (AVM) involves the vasculogenesis of cerebral blood vessels and can cause severe intracranial hemorrhage. Stromal cell-derived factor-1 (SDF-1) and its receptor, CXCR4, are believed to exert multiple physiological functions including angiogenesis. Thus, we investigated the role of SDF-1/CXCR4 in the vasculogenesis of cerebral AVM.

Methods

Brain AVM lesions from surgical resections were analyzed for the expression of SDF-1, CXCR4, VEGF-A, and HIF-1 by using immunohistochemical staining. Flow cytometry was used to quantify the level of circulating endothelial progenitor cells (EPCs). Further, in an animal study, chronic cerebral hypoperfusion model rats were analyzed for the expression of SDF-1 and HIF-1. CXCR4 antagonist, AMD3100, was also used to detect its effects on cerebral vasculogenesis and SDF-1 expression.

Results

Large amounts of CXCR4-positive CD45⁺ cells were found in brain AVM lesion blood vessel walls, which also have higher SDF-1 expression. Cerebral AVM patients also had higher level of EPCs and SDF-1. In chronic cerebral hypoperfusion rats, SDF-1, HIF-1, and CD45 expressions were elevated. The application of AMD3100 effectively suppressed angiogenesis and infiltration of CXCR4-positive CD45⁺ cells in hypoperfusion rats compared to controls.

Conclusion

The SDF-1/CXCR4 axis plays an important role in the vasculogenesis and migration of inflammatory cells in cerebral AVM lesions, possibly via the recruitment of bone marrow EPCs.

Polymorphisms in inflammatory and immune response genes associated with cerebral cavernous malformation type 1 severity

BACKGROUND

Familial cerebral cavernous malformation type 1 (CCM1) is an autosomal dominant disease caused by mutations in the Krev Interaction Trapped 1 (KRIT1/CCM1) gene, and characterized by multiple brain lesions that often result in intracerebral hemorrhage (ICH), seizures, and neurological deficits. Carriers of the same genetic mutation can present with variable symptoms and severity of disease, suggesting the influence of modifier factors. Evidence is emerging that inflammation and immune response play a role in the pathogenesis of CCM. The purpose of this study was to investigate whether common variants in inflammatory and immune response genes influence the severity of familial CCM1 disease, as manifested by ICH and greater brain lesion count.

METHODS

Hispanic CCM1 patients (n=188) harboring the founder Q455X 'common Hispanic mutation' (CHM) in the KRIT1 gene were analyzed at baseline. Participants were enrolled between June 2010 and March 2014 either through the Brain Vascular Malformation Consortium (BVMC) study or through the Angioma Alliance organization. Clinical assessment and cerebral susceptibility-weighted magnetic resonance imaging were performed to determine ICH as well as total and large (≥5 mm in diameter) lesion counts. Samples were genotyped on the Affymetrix Axiom Genome-Wide LAT1 Human Array. We analyzed 830 variants in 56 inflammatory and immune response genes for association with ICH and residuals of log-transformed total or large lesion count adjusted for age at enrollment and gender. Variants were analyzed individually or grouped by sub-pathways or whole pathways.

RESULTS

At baseline, 30.3% of CCM1-CHM subjects had ICH, with a mean ± standard deviation (SD) of 60.1±115.0 (range 0-713) for total lesions and 4.9±8.7 (range 0-104) for large lesions. The heritability estimates explained by all autosomal variants were 0.20 (SE=0.31), 0.81 (SE=0.17), and 0.48 (SE=0.19), for ICH, total lesion count, and large lesion count, respectively. TGFBR2 rs9823731 was significantly associated with ICH as well as with the total and large lesion counts (p≤0.017). Further, IL-4 rs9327638, CD14 rs778588, IL-6R rs114660934 and MSR1 rs62489577 were associated with two markers of disease severity. Finally, the whole pathway was associated with total lesion count (p=0.005) with TLR-4 rs10759930, CD14 rs778588, IL-6R rs114660934 and IGH rs57767447 mainly bearing this association. Eicosanoid signaling, extracellular pattern recognition, and immune response sub-pathways were also associated with the total lesion count.

CONCLUSIONS

These results suggest that polymorphisms in inflammatory and immune response pathways contribute to variability in CCM1 disease severity and might be used as predictors of disease severity. In particular, TGFBR2 rs9823731 was associated with all three markers of CCM1 disease severity tested, suggesting that TGFBR2 might be a key participant in the mechanism underlying CCM1 disease severity and phenotype variability. However, further longitudinal studies in larger sample sizes are needed to confirm these findings.

Ephrin B2 and EphB4 selectively mark arterial and venous vessels in cerebral arteriovenous malformation

OBJECTIVES

Ephrin type B receptor 4 (EphB4, Eph receptor) selectively binds ephrin B2 (Eph ligand). EphB4/ephrin B2 is involved in embryonic vessel development, vascular remodelling and pathological vessel formation in adults (including tumour angiogenesis). Binding of vascular endothelial growth factor (VEGF)-A to the endothelial-specific receptor VEGF receptor-2 is the main extracellular signal triggering angiogenic response. Little is known about the role of EphB4/ephrin B2 during angiogenesis and arteriovenous plasticity in cerebral arteriovenous malformation (cAVM). This study investigated EphB4 and ephrin B2 expression in cAVM.

METHODS

Haemorrhagic (H-AVM) and nonhaemorrhagic (NH-AVM) specimens of AVM nidus, obtained after microsurgical cAVM resection, and normal superficial temporal artery (STA) specimens, were analysed retrospectively. VEGF-A, EphB4 and ephrin B2 expression were studied by immunohistochemistry and immunoblotting.

RESULTS

In cAVM (10 H-AVM; 10 NH-AVM), VEGF-A was immunocytochemically localized to endothelial cells; strong endothelial cell staining was found for EphB4 in veins and ephrin B2 in arteries. Normal STA (n = 10) did not express EphB4 or ephrin B2. EphB4 and ephrin B2 expression was greater in H-AVM than in NH-AVM.

CONCLUSIONS

Endothelial cells are more active in H-AVM than NH-AVM. EphB4 and ephrin B2 play important roles in neovascularization and arteriovenous differentiation/plasticity. These data provide new insights into the aetiology of cAVM and lay a foundation for further study. The notch pathway induced by VEGF-A may be a key signalling pathway in this process.

Gene expression profiling of blood in brain arteriovenous malformation patients

Brain arteriovenous malformations (BAVMs) are an important cause of intracranial hemorrhage (ICH) in young adults. Gene expression profiling of blood has led to the identification of stroke biomarkers, and may help identify BAVM biomarkers and illuminate BAVM pathogenesis. It is unknown whether blood gene expression profiles differ between 1) BAVM patients and healthy controls, or 2) unruptured and ruptured BAVM patients at presentation. We characterized blood transcriptional profiles in 60 subjects (20 unruptured BAVM, 20 ruptured BAVM, and 20 healthy controls) using Affymetrix whole genome expression arrays. Expression differences between groups were tested by ANOVA, adjusting for potential confounders. Genes with absolute fold change ≥ 1.2 (false discovery rate corrected p ≤ 0.1) were selected as differentially expressed and evaluated for over-representation in KEGG biological pathways (p ≤ 0.05). Twenty-nine genes were differentially expressed between unruptured BAVM patients and controls, including 13 which may be predictive of BAVM. Patients with ruptured BAVM compared to unruptured BAVM differed in expression of 1490 genes, with over-representation of genes in 8 pathways including MAPK, VEGF, Wnt signaling and several inflammatory pathways. These results suggest clues to the pathogenesis of BAVM and/or BAVM rupture and point to potential biomarkers or new treatment targets.

Differential gene expression in relation to the clinical characteristics of human brain arteriovenous malformations

Arteriovenous malformations (AVMs) of the central nervous system are considered as congenital disorders. They are composed of abnormally developed dilated arteries and veins and are characterized microscopically by the absence of a capillary network. We previously reported DNA fragmentation and increased expression of apoptosis-related factors in AVM lesions. In this article, we used microarray analysis to examine differential gene expression in relation to clinical manifestations in 11 AVM samples from Japanese patients. We categorized the genes with altered expression into four groups: death-related, neuron-related, inflammation-related, and other. The death-related differentially expressed genes were MMP9, LIF, SOD2, BCL2A1, MMP12, and HSPA6. The neuron-related genes were NPY, S100A9, NeuroD2, S100Abeta, CAMK2A, SYNPR, CHRM2, and CAMKV. The inflammation-related genes were PTX3, IL8, IL6, CXCL10, GBP1, CHRM3, CXCL1, IL1R2, CCL18, and CCL13. In addition, we compared gene expression in those with or without clinical characteristics including deep drainer, embolization, and high-flow nidus. We identified a small number of genes. Using these microarray data we are able to generate and test new hypotheses to explore AVM pathophysiology. Microarray analysis is a useful technique to study clinical specimens from patients with brain vascular malformations.

An early venous abnormality: a potential cause of arteriovenous malformation recurrence

In adults, complete surgical resection of arteriovenous malformations (AVMs) is generally curative. Recurrence of AVMs is extremely rare and most often delayed over many years. The authors report the case of a man in his 20s with rapid AVM recurrence and dual blood supply from the dura and intracerebral vessels. Early recurrence of the AVM allowed documentation of the early events associated with this recurrence. This was evidenced by the first appearance of an early vein without any signs of abnormal vasculature, suggesting that abnormality of the venous drainage system might be an inciting event in the recurrence and perhaps genesis of AVMs.

Developmental origins of cerebrovascular disease I: prenatal cerebrovascular development--classic findings in the context of advances in genetic and fetal surveillance evaluations

Developmental origins of cerebrovascular disease should synchronize neuroscience advances with classic neurodevelopmental principles, as discussed in part 1 of this review. The ontogenetic interplay of nature and nurture influencing cerebrovascular development during the prenatal and early postnatal time periods should be considered when designing neuroprotective strategies, as discussed in part 2. Appreciation of adaptive and maladaptive effects of developmental neuroplasticity requires a systems biology approach that integrates molecular, receptor, cellular, neural network, and behavioral perspectives into structural and functional cerebrovascular phenotypes that express health or disease. Cognizance of the interrelationships among maternal, placental, fetal, and neonatal factors requires an interdisciplinary appreciation of genetic/epigenetic forces affecting neuroplasticity during early life, with later life effects. Knowledge of the multi-organ influences on cerebrovascular development broadens the systems biology perspective. Studies of positive and negative effects of neuroplasticity during early life must then consider ongoing gene-environment interactions during childhood and adulthood that either sustain neurologic health or contribute to disease.

Cavernous malformations

Cavernous malformations (CMs) are vascular lesions found in the central nervous system (CNS) and throughout the body and have been called cavernomas, cavernous angiomas, and cavernous hemangiomas. This article discusses the epidemiology, natural history, diagnosis, treatment and follow-up of children who are found to harbor these lesions. CMs affect children by causing hemorrhage, seizure, focal neurologic deficits, and headache. Diagnosis is best made with magnetic resonance imaging. Patients with multiple lesions should be referred for genetic evaluation and counseling. Individuals with symptomatic, growing, or hemorrhagic malformations should be considered for surgical resection. Close follow-up after diagnosis and treatment is helpful to identify lesion progression or recurrence.

Evidence of endothelial progenitor cells in the human brain and spinal cord arteriovenous malformations

BACKGROUND

Brain and spinal cord arteriovenous malformations (AVMs) are characterized by aberrant angiogenesis and vascular remodeling. Endothelial progenitor cells (EPCs) can be recruited by stromal cell-derived factor-1 (SDF-1), and participate in vascular remodeling in both physiological and pathological settings.

OBJECTIVE

To investigate whether there are increased EPC levels in the brain and spinal cord AVM nidus.

METHODS

Microsurgical specimens without endovascular embolization and radiosurgery from the brain (n = 12) and spinal cord (n = 5) AVMs were examined. Hemangioblastoma, meningioma, cerebral cortex obtained from epilepsy surgery, and the basilar artery from the autopsy were chosen for control comparisons. EPCs were identified as cells that were double-positive for the stem cell marker CD133 and the endothelial cell marker VEGFR-2 (vascular endothelial growth factor receptor-2 or KDR). In addition, SDF-1 was characterized by immunohistochemistry.

RESULTS

Both brain and spinal AVM tissues displayed more CD133-, SDF-1-, and CD68-positive signals than epilepsy and basilar artery control tissues. The level of EPCs was increased in the brain and spinal cord AVM nidus, mainly at the edge of the vessel wall. The expression of SDF-1 was colocalized with CD31-positive and α-smooth muscle cells, and was predominantly found within the vessel wall.

CONCLUSION

Our data demonstrate that EPCs are present in the nidus of the brain and spinal cord AVMs, which may mediate pathological vascular remodeling and impact the clinical course of AVMs.

A novel mouse model of cerebral cavernous malformations based on the two-hit mutation hypothesis recapitulates the human disease

Cerebral cavernous malformations (CCMs) are vascular lesions of the central nervous system appearing as multicavernous, blood-filled capillaries, leading to headache, seizure and hemorrhagic stroke. CCM occurs either sporadically or as an autosomal dominant disorder caused by germline mutation of one of the three genes: CCM1/KRIT1, CCM2/MGC4607 and CCM3/PDCD10. Surgically resected human CCM lesions have provided molecular and immunohistochemical evidence for a two-hit (germline plus somatic) mutation mechanism. In contrast to the equivalent human genotype, mice heterozygous for a Ccm1- or Ccm2-null allele do not develop CCM lesions. Based on the two-hit hypothesis, we attempted to improve the penetrance of the model by crossing Ccm1 and Ccm2 heterozygotes into a mismatch repair-deficient Msh2(-/-) background. Ccm1(+/-)Msh2(-/-) mice exhibit CCM lesions with high penetrance as shown by magnetic resonance imaging and histology. Significantly, the CCM lesions range in size from early-stage, isolated caverns to large, multicavernous lesions. A subset of endothelial cells within the CCM lesions revealed somatic loss of CCM protein staining, supporting the two-hit mutation mechanism. The late-stage CCM lesions displayed many of the characteristics of human CCM lesions, including hemosiderin deposits, immune cell infiltration, increased endothelial cell proliferation and increased Rho-kinase activity. Some of these characteristics were also seen, but to a lesser extent, in early-stage lesions. Tight junctions were maintained between CCM lesion endothelial cells, but gaps were evident between endothelial cells and basement membrane was defective. In contrast, the Ccm2(+/-)Msh2(-/-) mice lacked cerebrovascular lesions. The CCM1 mouse model provides an in vivo tool to investigate CCM pathogenesis and new therapies.

Brain arteriovenous malformation pathogenesis: a response-to-injury paradigm

Brain arteriovenous malformations (AVMs) are a rare but important cause of intracranial hemorrhage (ICH) in young adults. In this paper, we review both human and animal studies of brain AVM, focusing on the: (1) natural history of AVM hemorrhage, (2) genetic and expression studies of AVM susceptibility and hemorrhage, and (3) strategies for development of a brain AVM model in adult mice. These data target various mechanisms that must act in concert to regulate normal angiogenic response to injury. Based on the various lines of evidence reviewed in this paper, we propose a "response-to-injury" model of brain AVM pathogenesis.

Endovascular Treatment Increases but Gamma Knife Radiosurgery Decreases Angiogenic Activity of Arteriovenous Malformations

OBJECTIVE

To compare the angiogenic potentials of embolized, gamma knife–treated or untreated cerebral arteriovenous malformations (AVMs), using a rat cornea angiogenesis model.

METHODS

Tissue samples from cerebral AVM patients who were either untreated or had previously been treated with embolization or gamma knife radiosurgery and who had undergone operations for hemorrhage at the Neurosurgery Department or the Neurological Sciences Institute of Marmara University were used. For the macroscopic evaluation of angiogenesis, tissue samples were inoculated in a micropocket created on the rat eye, and the level of angiogenic activity was graded macroscopically for 15 days, with glioblastoma multiforme and normal brain artery tissues serving as positive and negative controls, respectively. For the other part of the experiment, eyes of another set of rats were inoculated with the study samples only using the same cornea angiogenesis model, in which microvessel count and vascular endothelial growth factor assessment was done at days 3, 7, 11, and 15.

RESULTS

Based on our macroscopic findings in the cornea angiogenesis model, embolized AVMs exhibited the highest angiogenic activity, followed by untreated AVMs and gamma knife–treated AVMs. Evaluations of vascular endothelial growth factor expression and microvessel counts showed a similar relation among the 3 tissue groups with regard to the level of angiogenic activity, supporting the results of macroscopic examinations.

CONCLUSION

This study, for the first time, provides experimental semiquantitative data to compare the angiogenic potentials of embolized and gamma knife–treated AVM tissues. Embolization may increase angiogenic activity, and gamma knife radiosurgery may decrease it when compared with activity in previously untreated AVMs. These data can be useful to understand why recurrence of AVMs after angiographically demonstrated endovascular occlusion is common but after gamma knife occlusion is rare.

Soluble endoglin modulates aberrant cerebral vascular remodeling

OBJECTIVE

Brain arteriovenous malformations (AVMs) are an important cause of neurological morbidity in young adults. The pathophysiology of these lesions is poorly understood. A soluble form of endoglin (sEng) has been shown to cause endothelial dysfunction and induce preeclampsia. We tested if sEng would be elevated in brain AVM tissues relative to epilepsy brain tissues, and also investigated whether sEng overexpression via gene transfer in the mouse brain would induce vascular dysplasia and associated changes in downstream signaling pathways.

METHODS

Expression levels of sEng in surgical specimens were determined by Western blot assay and enzyme-linked immunosorbent assay. Vascular dysplasia, levels of matrix metalloproteinase (MMP), and oxidative stress were determined by immunohistochemistry and gelatin zymography.

RESULTS

Brain AVMs (n = 33) had higher mean sEng levels (245 +/- 175 vs 100 +/- 60, % of control, p = 0.04) compared with controls (n = 8), as determined by Western blot. In contrast, membrane-bound Eng was not significantly different (108 +/- 79 vs 100 +/- 63, % of control, p = 0.95). sEng gene transduction in the mouse brain induced abnormal vascular structures. It also increased MMP activity by 490 +/- 30% (MMP-9) and 220 +/- 30% (MMP-2), and oxidants by 260 +/- 20% (4-hydroxy-2-nonenal) at 2 weeks after injection, suggesting that MMPs and oxidative radicals may mediate sEng-induced pathological vascular remodeling.

INTERPRETATION

The results suggest that elevated sEng may play a role in the generation of sporadic brain AVMs. Our findings may provide new targets for therapeutic intervention for patients with brain AVMs. Ann Neurol 2009;66:19-27.

EPHB4 gene polymorphisms and risk of intracranial hemorrhage in patients with brain arteriovenous malformations

BACKGROUND

Brain arteriovenous malformations (BAVMs) are a tangle of abnormal vessels directly shunting blood from the arterial to venous circulation and an important cause of intracranial hemorrhage (ICH). EphB4 is involved in arterial-venous determination during embryogenesis; altered signaling could lead to vascular instability resulting in ICH. We investigated the association of single-nucleotide polymorphisms (SNPs) and haplotypes in EPHB4 with risk of ICH at clinical presentation in patients with BAVM.

METHODS AND RESULTS

Eight haplotype-tagging SNPs spanning approximately 29 kb were tested for association with ICH presentation in 146 white patients with BAVM (phase I: 56 ICH, 90 non-ICH) using allelic, haplotypic, and principal components analysis. Associated SNPs were then genotyped in 102 additional cases (phase II: 37 ICH, 65 non-ICH), and data were combined for multivariable logistic regression. Minor alleles of 2 SNPs were associated with reduced risk of ICH presentation (rs314313_C, P=0.005; rs314308_T, P=0.0004). Overall, haplotypes were also significantly associated with ICH presentation (chi(2)=17.24, 6 df, P=0.008); 2 haplotypes containing the rs314308 T allele (GCCTGGGT, P=0.003; GTCTGGGC, P=0.036) were associated with reduced risk. In principal components analysis, 2 components explained 91% of the variance and complemented haplotype results by implicating 4 SNPs at the 5' end, including rs314308 and rs314313. These 2 SNPs were replicated in the phase II cohort, and combined data resulted in greater significance (rs314313, P=0.0007; rs314308, P=0.00008). SNP association with ICH presentation persisted after adjusting for age, sex, BAVM size, and deep venous drainage.

CONCLUSIONS

EPHB4 polymorphisms are associated with risk of ICH presentation in patients with BAVM, warranting further study.

Cerebral arteriovenous malformations. Part 1: cellular and molecular biology

Object

The scientific understanding of the nature of arteriovenous malformations (AVMs) in the brain is evolving. It is clear from current work that AVMs can undergo a variety of phenomena, including growth, remodeling, and/or regression—and the responsible processes are both molecular and physiological. A review of these complex processes is critical to directing future therapeutic approaches. The authors performed a comprehensive review of the literature to evaluate current information regarding the genetics, pathophysiology, and behavior of AVMs.

Methods

A comprehensive literature review was conducted using PubMed to reveal the molecular biology of AVMs as it relates to their complex growth and behavior patterns.

Results

Growth factors involved in AVMs include vascular endothelial growth factor, fibroblast growth factor, transforming growth factor β, angiopoietins, fibronectin, laminin, integrin, and matrix metalloproteinases.

Conclusions

Understanding the complicated molecular milieu of developing AVMs is essential for defining their natural history. Growth factors, extracellular matrix proteins, and other molecular markers will be the key to unlocking novel targeted drug treatments for these brain malformations.

Immune response in human cerebral cavernous malformations

BACKGROUND AND PURPOSE

Preliminary observations suggesting the presence of B and plasma cells and oligoclonality of immunoglobulin (Ig) G in cerebral cavernous malformations (CCM) have motivated a systematic study correlating the infiltration of the immune cells with clinical activity and antigen-triggered immune response in surgically excised lesions.

METHODS

Infiltration of plasma, B, T, and human leukocyte antigen-DR-expressing cells and macrophages within 23 excised CCM was related to clinical activity. Relative amounts of Ig isotypes were determined. IgG clonality of mRNA from CCM was assessed by spectratyping, cloning, and sequencing.

RESULTS

Infiltration of the immune cells ranged widely within CCM lesions, and cells were generally coexpressed with each other. Immune cell infiltration did not associate with recent bleeding and lesion growth. Significantly more B lymphocytes in CCM lesions were associated with venous anomaly. More T cells were present in solitary lesions. More T cells and less macrophages were present in CCM from younger subjects. IgG isotype was present in all CCM lesions. Most lesions also expressed IgM and IgA, with IgM predominance over IgA correlating with recent CCM growth. Oligoclonality was shown in IgG mRNA from CCM, but not from peripheral blood lymphocytes, with only 8 complementary-determining region 3 sequences observed among 134 clones from 2 CCM lesions.

CONCLUSIONS

An antigen-directed oligoclonal IgG immune response is present within CCM lesions regardless of recent clinical activity. Apparent differences in immune response in younger patients and in lesions with recent growth will need confirmation in other series. The pathogenicity of oligoclonal immune response will require systematic hypothesis testing in recently available CCM murine models.

ABERRANT ANGIOGENIC CHARACTERISTICS OF HUMAN BRAIN ARTERIOVENOUS MALFORMATION ENDOTHELIAL CELLS

OBJECTIVE

To identify and characterize the phenotypic and functional differences of endothelial cells derived from cerebral arteriovenous malformations (AVM), as compared with endothelial cells derived from a normal brain.

METHODS

Isolated AVM brain endothelial cells and control brain endothelial cells were evaluated immunohistochemically for expression of the endothelial cell markers von Willebrand factor and CD31, as well as angiogenic factors including vascular endothelial growth factor A, interleukin-8, and endothelin-1. Vascular endothelial growth factor receptors 1 and 2 were also evaluated using immunohistochemistry techniques. Functional assays evaluated cell proliferation, cytokine production, tubule formation, and cell migration using the modified Boyden chamber technique.

RESULTS

Endothelial cells derived from AVMs expressed high levels of vascular endothelial growth factor A and significantly overexpressed the vascular endothelial growth factor receptors 1 and 2 (P &lt; 0.05), as compared with control endothelial cells. In addition, comparison to control brain endothelial cells demonstrated that AVM brain endothelial cells proliferated faster, migrated more quickly, and produced aberrant tubule-like structures.

CONCLUSION

Endothelial cells derived from cerebral AVMs are highly activated cells overexpressing proangiogenic growth factors and exhibiting abnormal functions consistent with highly activated endothelial cells.

Evidence of inflammatory cell involvement in brain arteriovenous malformations

OBJECTIVE

Brain arteriovenous malformations (AVM) have high matrix metalloproteinase-9, interleukin-6, and myeloperoxidase (MPO) expression, and polymorphic variations in inflammatory genes are associated with an increased risk of hemorrhage. In this study, we characterized the presence of inflammatory cells in AVM lesional tissue specimens.

METHODS

Immunohistochemistry was used to identify and localize neutrophils (MPO as marker), macrophages/microglia (CD68 as marker), T lymphocytes (CD3 as marker), and B lymphocytes (CD20 as marker). Endothelial cell (EC) marker CD31 was used as an index to assess vascular mass (EC mass). Surgical specimens from 20 unruptured, nonembolized AVMs were examined; seven cortical samples from temporal lobectomy were used as controls. Positive signals for inflammatory cell markers were counted and analyzed by normalizing to the area of the tissue section and the amount of endothelial cells (cells/mm/EC mass pixels). Levels of MPO and matrix metalloproteinase 9 were determined by enzyme-linked immunosorbent assay.

RESULTS

Neutrophils and macrophages are all frequently identified in the vascular wall of AVM tissue. In contrast, T and B lymphocytes are rarely observed in AVM tissue. AVM tissue displayed more neutrophil and macrophage/microglia markers than epilepsy control tissue (MPO: 434 +/- 333 versus 5 +/- 4, P = 0.0001; CD68: 454 +/- 404 versus 4 +/- 2, P = 0.0001; cells/mm/EC mass pixels). In ex vivo studies, neutrophil quantity, MPO, and matrix metalloproteinase-9 levels were all colinear (R = 0.98-0.99).

CONCLUSION

Our study demonstrates that inflammatory cells are present in AVM tissue. Taken together with previous genetic and cytokine studies, these data are consistent with a novel view that inflammation is associated with AVM disease progression and rupture.

Increased tissue perfusion promotes capillary dysplasia in the ALK1-deficient mouse brain following VEGF stimulation

Loss-of-function activin receptor-like kinase 1 gene mutation (ALK1+/-) is associated with brain arteriovenous malformations (AVM) in hereditary hemorrhagic telangiectasia type 2. Other determinants of the lesional phenotype are unknown. In the present study, we investigated the influence of high vascular flow rates on ALK1+/- mice by manipulating cerebral blood flow (CBF) using vasodilators. Adult male ALK1+/- mice underwent adeno-associated viral-mediated vascular endothelial growth factor (AAVVEGF) or lacZ (AAVlacZ as a control) gene transfer into the brain. Two weeks after vector injection, hydralazine or nicardipine was infused intraventricularly for another 14 days. CBF was measured to evaluate relative tissue perfusion. We analyzed the number and morphology of capillaries. Results demonstrated that hydralazine or nicardipine infusion increased focal brain perfusion in all mice. It was noted that focal CBF increased most in AAVVEGF-injected ALK1+/- mice following hydralazine or nicardipine infusion (145+/-23% or 150+/-11%; P<0.05). There were more detectable dilated and dysplastic capillaries (2.4+/-0.3 or 2.0+/-0.4 dysplasia index; P<0.01) in the brains of ALK1+/- mice treated with AAVVEGF and hydralazine or nicardipine compared with the mice treated with them individually. We concluded that increased focal tissue perfusion and angiogenic factor VEGF stimulation could have a synergistic effect to promote capillary dysplasia in a genetic deficit animal model, which may have relevance to further studies of AVMs.

Surgery of cerebral arteriovenous malformations

Despite remarkable progress, the microsurgical extirpation of cerebral arteriovenous malformations (AVMs) even by experienced neurosurgeons is not always easy or safe. This article focuses on how to render AVM surgery safer, and offers strategies and tactics for avoiding perilous bleeding and preserving postoperative neurological function. Our treatment strategies and surgical techniques are offered from the operating surgeon's perspective. An understanding of pathophysiology of cerebral AVMs is important for their appropriate surgical treatment. Sophisticated neuroimaging techniques and scrupulous neurophysiological examinations alert to possible complications, and improved surgical approaches help to minimize the sequelae of unanticipated complications. At the early stage of cerebral AVM surgery, extensive dissection of the sulci, fissures, and subarachnoid cistern should be performed to expose feeders, nidus, and drainers. Problems with the surgery of large and/or deep-seated lesions are exacerbated when arterial bleeding from the nidus continues even after all major feeders are thought to have been occluded. We routinely place catheters for angiography at the surgery of complex AVMs to find missing feeding arteries or to identify the real-time hemodynamic status of the lesion. Temporary clip application on feeders and less coagulation of the nidus is necessary to control intranidal pressure and to avoid uncontrollable bleeding from the nidus and adjacent brain. Intraoperative navigation images superimposed on tractography images can provide us with valuable information to minimize neurological deficits. Deeper insight into AVM nature and into events that occur during AVM surgery as well as the inclusion of molecular biological approaches will open new horizons for the safe and effective treatment of AVMs.