Neurovascular manifestations in hereditary hemorrhagic telangiectasia: imaging features and genotype-phenotype correlations.

BACKGROUND AND PURPOSE: Hereditary hemorrhagic telangiectasia is an autosomal dominant disease that presents in 10%-20% of patients with various brain vascular malformations. We aimed to report the radiologic features (phenotype) and the genotype-phenotype correlations of brain vascular malformations in hereditary hemorrhagic telangiectasia. MATERIALS AND METHODS: Demographic, clinical, genotypic, and imaging information of 75 patients with hereditary hemorrhagic telangiectasia with brain arteriovenous malformations enrolled in the Brain Vascular Malformation Consortium from 2010 to 2012 were reviewed. RESULTS: Nonshunting, small, superficially located conglomerates of enhancing vessels without enlarged feeding arteries or draining veins called "capillary vascular malformations" were the most commonly observed lesion (46 of 75 patients; 61%), followed by shunting "nidus-type" brain AVMs that were typically located superficially with a low Spetzler-Martin Grade and a small size (32 of 75 patients; 43%). Direct high-flow fistulous arteriovenous shunts were present in 9 patients (12%). Other types of vascular malformations (dural AVF and developmental venous anomalies) were present in 1 patient each. Multiplicity of vascular malformations was seen in 33 cases (44%). No statistically significant correlation was observed between hereditary hemorrhagic telangiectasia gene mutation and lesion type or lesion multiplicity. CONCLUSIONS: Depending on their imaging features, brain vascular malformations in hereditary hemorrhagic telangiectasia can be subdivided into brain AVF, nidus-type AVM, and capillary vascular malformations, with the latter being the most common phenotype in hereditary hemorrhagic telangiectasia. No genotype-phenotype correlation was observed among patients with this condition.

Beta-adrenergic receptor polymorphisms and cardiac graft function in potential organ donors.

Prior studies have demonstrated associations between beta-adrenergic receptor (ßAR) polymorphisms and left ventricular dysfunction-an important cause of allograft nonutilization for transplantation. We hypothesized that ßAR polymorphisms predispose donor hearts to LV dysfunction after brain death. A total of 1043 organ donors managed from 2001-2006 were initially studied. The following ßAR single nucleotide polymorphisms were genotyped: ß1AR 1165C/G (Arg389Gly), ß1AR 145A/G (Ser49Gly), ß2AR 46G/A (Gly16Arg) and ß2AR 79C/G (Gln27Glu). In multivariable regression analyses, the ß2AR46 SNP was significantly associated with LV systolic dysfunction, with each minor allele additively decreasing the odds for LV ejection fraction <50%. The ß1AR1165 and ß2AR46 SNPs were associated with higher dopamine requirement during the donor management period: donors with the GG and AA genotypes had ORs of 2.64 (95% CI 1.52-4.57) and 2.70 (1.07-2.74) respectively for requiring >10 µg/kg/min of dopamine compared to those with the CC and GG genotypes. However, no significant associations were found between ßAR SNPs and cardiac dysfunction in 364 donors managed from 2007-2008, perhaps due to changes in donor management, lack of power in this validation cohort, or the absence of a true association. ßAR polymorphisms may be associated with cardiac dysfunction after brain death, but these relationships require further study in independent donor cohorts.

Pediatric intracranial nongalenic pial arteriovenous fistulas: clinical features, angioarchitecture, and outcomes.

BACKGROUND AND PURPOSE: NGAVFs are rare vascular malformations usually presenting in infancy or childhood. We sought to identify clinical and angiographic predictors of clinical outcome for these lesions. MATERIALS AND METHODS: Retrospective review of a neurointerventional data base identified 386 pediatric patients with intracranial AVFs and AVMs, from which a cohort of 25 patients with NGAVF were selected for medical record and imaging analysis. RESULTS: NGAVFs constituted 7.3% of pediatric intracranial vascular lesions with a nondural arteriovenous shunt. Seven of 8 patients who presented in the first month of life had CHF and harbored large, complex fistulas with multiple sites of arteriovenous shunting. Single-hole fistulas predominated later in childhood and more frequently presented with seizures, hemorrhage, or focal neurologic deficits. More treatment procedures were performed in subjects presenting at ≤ 2 years of age compared with older children (median = 3 versus 2, P = .041), and in those harboring a multi-hole fistula versus those with a single-hole fistula (median = 3 versus 2, P = .003). Eighteen patients (72%) had complete posttreatment elimination of NGAVF shunting. Compared with patients presenting at >2 years of age, patients presenting in the first 2 years of life were more likely to have a multi-hole fistula (100% versus 25%, P = .0001) and to have a poor clinical outcome (54% versus 0%, P = .0052), defined as a pediatric mRS of ≥ 3. CONCLUSIONS: The morbidity of NGAVF appears higher than previously reported despite a somewhat higher rate of angiographic cure. Poor clinical outcome occurred primarily in patients with multi-hole NGAVFs presenting at ≤ 2 years of age.

The 4G/4G genotype of the PAI-1 (serpine-1) 4G/5G polymorphism is associated with decreased lung allograft utilization.

Widespread thrombi are found among donor lungs rejected for transplantation. The 4G/5G polymorphism in the plasminogen activator inhibitor (PAI-1) gene impacts transcription and the 4G allele is associated with increased PAI-1 levels. We hypothesized that the 4G/4G genotype would be associated with decreased lung graft utilization, potentially because of worse oxygenation in the donor. We genotyped donors managed by the California Transplant Donor Network from 2001 to 2008 for the 4G/5G polymorphism in the PAI-1 gene. Non-Hispanic donors from 2001 to 2005 defined the discovery cohort (n = 519), whereas donors from 2006 to 2008 defined the validation cohort (n = 369). We found, that the odds of successful lung utilization among Non-Hispanic white donors were lower among donors with the 4G/4G genotype compared to those without this genotype in both the discovery (OR = 0.55, 95% CI = 0.3-0.9, p = 0.02) and validation (OR = 0.5, 95% CI = 0.3-0.9, p = 0.03) cohorts. This relationship was independent of age, gender, cause of death, drug use and history of smoking. Donors with the 4G/4G genotype also had a lower PaO2/FiO2 ratio (p = 0.03) and fewer donors with the 4G/4G genotype achieved the threshold PaO2/FiO2 ratio ≥ 300 (p = 0.05). These findings suggest a role for impaired fibrinolysis resulting in worse gas exchange and decreased donor utilization.

Neonatal giant pial arteriovenous malformation: genesis or rapid enlargement in the third trimester.

A neonate with congestive heart failure at birth due to a nearly holohemispheric pial arteriovenous malformation is described. This occurred despite a normal second trimester prenatal sonogram. Successful treatment of heart failure was achieved by embolization alone. This case demonstrates that hemodynamically significant lesions may arise later or enlarge more rapidly in utero than previously thought.

Development of a cerebral microvascular dysplasia model in rodents.

Normal vasculature development of the central nervous system is extremely important because patients with vascular malformations are at life-threatening risk for intracranial hemorrhage or cerebral ischemia. The etiology and pathogenesis of abnormal vasculature development in the central nervous system are unknown, and progress is hampered by the lack of animal models for human cerebrovascular diseases. Here, we report our current study on cerebral microvascular dysplasia (CMVD) development. Using vascular endothelial growth factor hyper-stimulation, we demonstrated that aberrant microvessels could be developed in the rodent brain under certain conditions (such as genetic deficient background, local cytokine and chemokine release, or exogenous vessel dilating stimulation) that may speed up focal angiogenesis and lead to cerebral vascular dysplasia.

Genetic considerations relevant to intracranial hemorrhage and brain arteriovenous malformations.

Brain arteriovenous malformations (AVMs) cause intracranial hemorrhage (ICH), especially in young adults. Molecular characterization of lesional tissue provides evidence for involvement of both angiogenic and inflammatory pathways, but the pathogenesis remains obscure and medical therapy is lacking. Abnormal expression patterns have been observed for proteins related to angiogenesis (e.g., vascular endothelial growth factor, angiopoietin-2, matrix metalloproteinase-9), and inflammation (e.g., interleukin-6 [IL-6] and myeloperoxidase). Macrophage and neutrophil invasion have also been observed in the absence of prior ICH. Candidate gene association studies have identified a number of germline variants associated with clinical ICH course and AVM susceptibility. A single nucleotide polymorphism (SNP) in activin receptor-like kinase-1 (ALK-1) is associated with AVM susceptibility, and SNPs in IL-6, tumor necrosis factor-alpha (TNF-alpha), and apolipoprotein-E (APOE) are associated with AVM rupture. These observations suggest that even without a complete understanding of the determinants of AVM development, the recent discoveries of downstream derangements in vascular function and integrity may offer potential targets for therapy development. Further, biomarkers can now be established for assessing ICH risk. These data will generate hypotheses that can be tested mechanistically in model systems, including surrogate phenotypes, such as vascular dysplasia and/or models recapitulating the clinical syndrome of recurrent spontaneous ICH.

Numerical modeling of the flow in intracranial aneurysms: prediction of regions prone to thrombus formation.

The deposition of intralumenal thrombus in intracranial aneurysms adds a risk of thrombo-embolism over and above that posed by mass effect and rupture. In addition to biochemical factors, hemodynamic factors that are governed by lumenal geometry and blood flow rates likely play an important role in the thrombus formation and deposition process. In this study, patient-specific computational fluid dynamics (CFD) models of blood flow were constructed from MRA data for three patients who had fusiform basilar aneurysms that were thrombus free and then proceeded to develop intralumenal thrombus. In order to determine whether features of the flow fields could suggest which regions had an elevated potential for thrombus deposition, the flow was modeled in the baseline, thrombus-free geometries. Pulsatile flow simulations were carried out using patient-specific inlet flow conditions measured with MR velocimetry. Newtonian and non-Newtonian blood behavior was considered. A strong similarity was found between the intra-aneurysmal regions with CFD-predicted slow, recirculating flows and the regions of thrombus deposition observed in vivo in the follow-up MR studies. In two cases with larger aneurysms, the agreement between the low velocity zones and clotted-off regions improved when non-Newtonian blood behavior was taken into account. A similarity was also found between the calculated low shear stress regions and the regions that were later observed to clot.

Monitoring serial change in the lumen and outer wall of vertebrobasilar aneurysms.

BACKGROUND AND PURPOSE: Estimation of the stability of fusiform aneurysms of the basilar artery requires precise monitoring of the luminal and outer wall volumes. In this report we describe the use of MR imaging and 3D postprocessing methods to study the evolution of those aneurysms. MATERIALS AND METHODS: Nine patients with fusiform basilar artery aneurysms underwent MR imaging studies covering at least 2 different time points (mean delay between studies, 7.1 +/- 4.6 months). Imaging included multisection 2D T1-weighted fast spin-echo and/or 3D steady-state imaging to assess the outer wall and contrast-enhanced MR angiography to study the lumen. The outer and inner walls were extracted using, respectively, a manual delineation (made by 2 observers) and a thresholding technique. The 2 studies were subsequently coregistered at each time point, as well as between differing time points. Volumes of each vessel component were calculated. RESULTS: Mean volume was 6760 +/- 6620 mm(3) for the outer wall and 2060 +/- 1200 mm(3) for the lumen. Evolution of the lumen and outer wall was highly variable from 1 patient to another, with a trend toward increase of the vessel wall for the largest aneurysms. Interobserver reproducibility for outer wall delineation was on the order of 90%. CONCLUSION: Combining MR imaging methods to study both the outer wall and lumen with 3D registration tools provides a powerful method for progression of fusiform basilar aneurysmal disease.

Adeno-associated viral vector-mediated hypoxia-regulated VEGF gene transfer promotes angiogenesis following focal cerebral ischemia in mice.

Uncontrolled expression of vascular endothelial growth factor (VEGF) in vivo may cause unexpected side effects, such as brain hemangioma or tumor growth. Because hypoxia-inducible factor-1 (HIF-1) is upregulated during cerebral ischemia and regulates gene expression by binding to a cis-acting hypoxia-responsive element (HRE), we therefore used a novel HRE, originating in the 3'-end of the erythropoietin (Epo) gene, to control gene expression in the ischemic brain. A concatemer of nine copies (H9) of the consensus sequence of HRE was used to mediate hypoxia induction. Three groups of adult CD-1 mice received AAVH9-VEGF, AAVH9-lacZ or saline injection, and then underwent 45 min of transient middle cerebral artery occlusion (tMCAO). Results show that HIF-1 was persistently expressed in the ischemic brain. VEGF was overexpressed in the ischemic perifocal region in AAVH9-VEGF-transduced mice. Double-labeled immunostaining showed that VEGF expressed in neurons and astrocytes but not endothelial cells, suggesting that adeno-associated virus (AAV) vectors transduced neurons and astrocytes predominantly. The total number of microvessels/enlarged microvessels was greatly increased in the AAVH9-VEGF-transduced mice (180+/-29/27+/-4) compared to the AAVH9-lacZ (118+/-19/14+/-3) or saline-treated (119+/-20/14+/-2) mice after tMCAO (P<0.05). Cell proliferation examination demonstrated that these microvessels were newly formed. Regional cerebral blood flow recovery in the AAVH9-VEGF-transduced mice was also better than in AAVH9-lacZ or saline-treated mice (P<0.05). Our data indicated that HRE is a novel trigger for the control of VEGF expression in the ischemic brain. VEGF overexpression through AAVH9-VEGF gene transfer showed stable focal angiogenic effects in post-ischemic repair process, providing an opportunity to rebuild injured brain tissue.

Effects of angiopoietin-1 on vascular endothelial growth factor-induced angiogenesis in the mouse brain.

A better understanding of angiogenic factors and their effects on angiogenesis in brain is necessary to treat cerebral vascular disorders such as ischemic brain injury. Vascular endothelial growth factor (VEGF) induces angiogenesis and increases blood-brain barrier (BBB) permeability in adult mouse brain. The effect of angiopoietin-1 on BBB leakage during the angiogenesis process is unclear. We sought to identify the effects of combining VEGF with angiopoietin-1 on cerebral angiogenesis and BBB. Adult male CD-1 mice underwent AdFc (adenoviral vector control), AdAng-1, VEGF protein, VEGF protein plus AdAng-1, or saline (negative control) injection. Brain microvessels were counted using lectin staining on tissue sections after 2 weeks of adenoviral gene transfer. The presence of zonula occludens-1 (ZO-1) was determined by Western blot analysis and immunohistochemistry. Microvessel count and augmented capillary diameter increased in mice treated with either VEGF protein or AdAng-1 plus VEGF protein compared to saline, AdFc, or AdAng-1 alone (p < 0.05). Double-labeled immunostaining demonstrated that ZO-1-positive staining was more complete on the microvessel wall in the AdAng-1 and AdAng-1 plus VEGF protein treated group compared to VEGF protein group. The results of ZO-1 expression from Western blot analysis paralleled that from immunohistochemistry (p < 0.05). We conclude that focal VEGF and angiopoietin-1 hyperstimulation in mouse brain increases microvessel density while maintaining ZO-1 protein expression, suggesting that angiopoietin-1 plays a role in synergistically inducing angiogenesis and BBB integrity.

Distinguishing intracerebral hemorrhages caused by arteriovenous malformations.

BACKGROUND: There is a shortage of data addressing the clinical characteristics of patients with arteriovenous malformations (AVMs) who present with intracerebral hemorrhages (ICH). METHODS: A retrospective cohort study of members of a large, pre-paid health care program was conducted to identify factors that distinguish ICH secondary to cerebral AVMs from all other causes. Univariate and multivariate analysis was performed using Student's t test, Wilcoxon rank-sum test, and logistic regression. RESULTS: Patients with an underlying AVM were younger and more likely to be female, non-smokers with lower blood pressures, lower cholesterol, and lower white blood cell counts on presentation. CONCLUSIONS: These clinical characteristics may be useful in defining potential risk factors in future prospective studies as well as targeting candidates for additional imaging studies after ICH with no apparent etiology.

Lack of flow regulation may explain the development of arteriovenous malformations.

In the normal vasculature, vessels of widely different sizes maintain shear stress within a narrow range. Recently, investigators have had great success using mathematical models to explore the relationship of structure to function in normal vascular beds. When investigators first explored how vascular beds adapt to set shear stress at appropriate levels, however, some vessels tended to regress, and some tended to grow into arteriovenous shunts. Degeneration of the arterial tree is prevented when flow regulation is added to the model. The present work explores the implication of this theoretical development and illustrates how it may explain the genesis of arteriovenous malformations (AVMs). We use a simple model to illustrate how impairing local control of blood flow causes models to become structurally unstable, yielding a structure and behavior similar to AVMs. This work shows how the lack of local flow control can be the cause, not just the result, of arteriovenous malformations. With insight gained from this modeling approach, specific, focused experiments can be designed.

Evidence of increased endothelial cell turnover in brain arteriovenous malformations.

OBJECTIVE: We hypothesized that human brain arteriovenous malformations (BAVMs) are nonstatic vascular lesions with active angiogenesis or vascular remodeling. To test this hypothesis, we assessed endothelial cell turnover in BAVMs. METHODS: We identified nonresting endothelial cells by use of immunohistochemistry for the Ki-67 antigen. From archived paraffin blocks, we selected BAVM vessels without intravascular thrombosis or embolic material in areas nonadjacent to the nidus edge. For controls, we used 50- to 100-microm diameter cortical vessels from temporal lobe cortex removed for epilepsy treatment. The Ki-67 index was calculated as a percentage of Ki-67-positive endothelial cells. The data were analyzed by the nonparametric Mann-Whitney test and reported as mean +/- standard deviation. RESULTS: Thirty-seven specimens that met the above criteria were selected. There were 26 +/- 15 vessels counted in each BAVM specimen versus 18 +/- 5 in each control cortex (n = 5). The mean Ki-67 index was higher for BAVM vessels than control cortical vessels (0.7 +/- 0.6 versus 0.1 +/- 0.2%; P = 0.005), which represented an approximately seven-fold increase in the number of nonresting endothelial cells. In the BAVM group, there was a trend for younger patients to have a wider variation and higher Ki-67 index than older patients; no trend was evident in the control group. CONCLUSION: Compared with control vessels, BAVM vessels have higher endothelial cell turnover, which suggests the presence of active angiogenesis or vascular remodeling in BAVMs.

Abnormal balance in the angiopoietin-tie2 system in human brain arteriovenous malformations.

Brain arteriovenous malformations (BAVMs) are congenital vascular lesions that often present as cerebral hemorrhage in young adults. The variable nature of the clinical course, especially with respect to spontaneous hemorrhage, recurrence, growth, and regression, suggests that BAVMs are lesions with active angiogenesis and vascular remodeling. We examined mRNA and protein expression of angiopoietin 1 (Ang1) and Ang2 by semiquantitative reverse transcriptase-polymerase chain reaction, in situ hybridization, and Western blot in BAVMs and control brains obtained from temporal lobectomy for medically intractable seizures. Although Ang1 mRNA levels were similar in BAVMs and controls, Ang1 protein levels were 30% lower in BAVMs than in controls. Ang2 mRNA levels were 40% higher and Ang2 protein levels were 8-fold higher in BAVMs than in controls. In situ hybridization showed that the Ang2 mRNA was localized to the perivascular area in BAVMs. This abnormal balance in the Ang-Tie2 system may, in part, explain the aberrant vascular phenotype in BAVMs.

Recovery of brain function during induced cerebral hypoperfusion.

We used the setting of clinically indicated internal carotid artery balloon test occlusions in 44 patients with inoperable carotid cavernous aneurysms or head and neck tumours to examine real-time changes in higher cerebral function that correlate with specific levels of cerebral blood flow. By making detailed haemodynamic and neurobehavioural measurements during the 30 min the carotid artery was occluded, we were able to quantify higher cerebral function patterns in relation to absolute cerebral blood flow (CBF) levels. We found that once the carotid artery was occluded, patients whose CBF averaged 47 ml/100 g/min (no different from baseline) maintained consistent performance on a sustained attention task; those whose CBF dropped to an average 37 ml/100 g/min had a reversible deterioration of sustained attention, and those whose CBF fell to 27 ml/100 g/min had impaired sustained attention that persisted until the carotid occlusion was reversed. The relevance of these results to the pathological state of clinical stroke is discussed with respect to the haemodynamic and physiological mechanisms that may determine how brain function is lost and regained in the setting of acute cerebral hypoperfusion.