Evaluation of fetal cerebrovascular circulation and brain development: the role of ultrasound and Doppler

Change over time in internal cerebral vein pulsation in premature infants at risk of intraventricular hemorrhage

BACKGROUND

Prolonged continuation of augmented internal cerebral vein (ICV) pulsation may be related to the development of premature intraventricular hemorrhage (IVH). However, the characteristics of ICV flow patterns in premature infants are unclear.

AIM

To investigate the changes over time in ICV pulsation in premature infants at risk of IVH.

STUDY DESIGN

A 5-year retrospective observational study of a single-center trial.

SUBJECTS

In total, 112 very-low-birth-weight infants with gestational age of ≤32 weeks.

OUTCOME MEASURES

ICV flow was measured every 12 h until 96 h after birth and thereafter on days 7, 14, and 28. The ICV pulsation index (ICVPI), which is a ratio of the minimum/maximum speed of ICV flow, was calculated. We recorded longitudinal ICVPI change and compared ICVPI among three groups classified according to gestational age.

RESULTS

ICVPI started declining after day 1 and reached the minimum median value in 49-60 h after birth (1.0 during 0-36 h, 0.9 during 37-72 h, and 1.0 after 73-84 h). ICVPI was significantly lower during 25-96 h than during 0-24 h and on days 7, 14, and 28. ICVPI in the 23-25-week group was significantly lower between 13-24 h and day 14 than that in the 29-32-week group, and the same was observed for the 26-28-week group between 13-24 h and 49-60 h.

CONCLUSIONS

ICV pulsation was affected by time after birth and gestational age, and this ICVPI fluctuation may reflect a postnatal circulatory adaptation.

Impaired pulmonary function mediates the impact of preterm birth on later-life stroke: a 2-step, multivariable Mendelian randomization study

OBJECTIVES

Observational studies have suggested an association between preterm birth and stroke in late adulthood, but it remains unclear whether the association is causal. The purpose of this study was to evaluate the causal effects of gestational age on stroke and to determine the pathophysiological mechanisms underlying the causal associations.

METHODS

Two-sample Mendelian randomization (MR) was performed to assess the causal effects of fetal gestational duration, early preterm birth (EPB), preterm birth, or postterm birth on stroke and its subtypes. Two-step Mendelian randomization (TSMR) and multivariable Mendelian randomization (MVMR) were additionally used to determine the role of common stroke risk factors, including cardiovascular diseases, hypertension, pulmonary impairment, inflammation, and metabolic diseases, in mediating the causal associations between gestational age and stroke and its subtypes.

RESULTS

Genetically predicted EPB increased the risk of cardioembolic stroke (CES; odds ratio [OR], 1.115; 95% confidence interval [CI], 1.036 to 1.200; p=0.004) and large artery stroke (LAS; OR, 1.131; 95% CI, 1.031 to 1.241; p=0.009). The TSMR results showed that EPB was associated with a lower forced expiratory volume in the first second and forced vital capacity ratio (FEV1/FVC) (β=-0.020; 95% CI, -0.035 to -0.005; p=0.009), which increased the risk of CES and LAS. Further MVMR analysis showed that the associations between EPB and stroke disappeared after adjustment for FEV1/FVC.

CONCLUSIONS

Our data demonstrate that EPB is causally associated with an elevated risk of CES and LAS, and that pulmonary dysfunction mediates the causal impact of EPB on CES and LAS.

Age-dependent Intracranial Artery Morphology in Healthy Children

PURPOSE

Evaluation of intracranial artery morphology plays an important role in diagnosing a variety of neurovascular diseases. In addition to clinical symptoms, diagnosis currently relies on qualitative rather than quantitative evaluation of vascular imaging sequences, such as magnetic resonance angiography (MRA). However, there is a paucity of literature on normal arterial morphology in the pediatric population across brain development. We aimed to quantitatively assess normal, age-related changes in artery morphology in children.

METHODS

We performed retrospective analysis of pediatric MRA data obtained from a tertiary referral center. An MRA dataset from 98 children (49 boys/49 girls) aged 0.6-20 years (median = 11.5 years) with normal intracranial vasculature was retrospectively collected between 2011 and 2018. All arteries were automatically segmented to determine the vessel radius. Using an atlas-based approach, the average radius and density of arteries were measured in the three main cerebral vascular territories and the radius of five major arteries was determined at corresponding locations.

RESULTS

The radii of the major arteries as well as the average artery radius and density in the different vascular territories in the brain remained constant throughout childhood and adolescence (|r| < 0.369 in all cases).

CONCLUSION

This study presents the first automated evaluation of intracranial vessel morphology on MRA across childhood. Our results can serve as a framework for quantitative evaluation of cerebral vessel morphology in the setting of pediatric neurovascular diseases.

Perinatal stroke

Perinatal stroke is a heterogeneous syndrome resulting from brain injury of vascular origin that occurs between 20 weeks of gestation and 28 days of postnatal life. The incidence of perinatal stroke is estimated to be between 1:1600 and 1:3000 live births (approximately 2500 children per year in the United States), though its actual incidence is difficult to estimate because it is likely underdiagnosed. Perinatal arterial ischemic stroke (PAIS) accounts for approximately 70% of cases of perinatal stroke. Cerebral sinovenous thrombosis, while less common, also accounts for a large proportion of the morbidity and mortality seen with perinatal stroke. Hemorrhagic stroke leads to disruption of neurologic function due to intracerebral hemorrhage that is nontraumatic in origin. While most cases of PAIS fall into one of these three categories, other patterns of injury should also be considered perinatal stroke. In some cases, the etiology of PAIS is not known but is idiopathic. This chapter will review the classification, risk factors, pathogenesis, clinical presentation, management, and long-term sequelae of perinatal stroke.

Cerebral blood flow dynamic in foetuses with hypoplastic left heart syndrome: Incremental value of the first segment of the anterior cerebral artery over the middle cerebral artery?

OBJECTIVE

To investigate the blood flow Doppler parameters of the anterior cerebral artery (ACA) in foetuses with hypoplastic left heart syndrome (HLHS).

METHODS

Doppler parameters (peak systolic velocity [PSV], end-diastolic velocity [EDV], time-averaged maximum velocity [TAMXV] and pulsatility index [PI]) and biometric parameters were measured in two anatomical segments of the ACA (S1 and S2) and in the middle cerebral artery (MCA) in 35 HLHS foetuses and 73 gestational age-matched normal foetuses. Correlations between the cerebral artery PIs and head circumference (HC) were assessed.

RESULTS

Both EDV and TAMXV of the ACA and MCA in the HLHS group were significantly higher than in the normal group (P < .05). The PI of the ACA and MCA in the HLHS group were significantly lower than in the normal group (P < .05). ACAS1PI and ACAS2PI in the HLHS foetuses with retrograde blood flow in the aortic isthmus (AoI) were significantly lower than those of HLHS foetuses without retrograde blood flow in the AoI (P < .05). ACAS2PI was significantly lower than ACAS1PI in the HLHS foetuses with retrograde blood flow in the AoI (P = .047). The abnormal rates of ACAS1 and ACAS2 were significantly higher than that of the MCA (P < .05) in the HLHS group. The HC and biparietal diameter were significantly lower in the HLHS group than in the control group (P < .05). HC was correlated with the PIs of ACAS1, ACAS2 and the MCA in the HLHS group (P < .05).

CONCLUSION

A redistribution of foetal cerebral blood flow appeared in HLHS, and the measurement of ACA PI might provide early information on brain hypoxia.

Genetic and Environmental Contributions to Variation in the Posterior Communicating Collaterals of the Circle of Willis

Variation in blood flow mediated by the posterior communicating collateral arteries (PComs) contributes to variation in the severity of tissue injury in obstructive disease. Evidence in animals and humans indicates that differences in the extent of PComs, i.e., their anatomic lumen diameter and whether they are present bilaterally, unilaterally, or absent, are a major factor. These differences arise during development since they are present at birth. However, the causal mechanisms are unknown. We used angiography after maximal dilation to examine involvement of genetic, environmental, and stochastic factors. The extent of PComs varied widely among seven genetically diverse strains of mice. Like pial collaterals in the microcirculation, aging and hypertension reduced PCom diameter, while in contrast, obesity, hyperlipidemia, metabolic syndrome, and diabetes mellitus had no effect. Naturally occurring intrauterine growth restriction had no effect on extent of PCom or pial collaterals in the adult. The number and diameter of PComs evidenced much larger apparent stochastic-dependent variation than pial collaterals. In addition, both PComs underwent flow-mediated outward remodeling after unilateral permanent MCA occlusion that varied with genetic background and was greater on the ipsilesional side. These findings indicate that variation in the number and diameter of PCom collateral arteries arises from stochastic factors and naturally occurring genetic variants that differ from those that cause variation in pial collateral arterioles. Environmental factors also contribute: aging and hypertension reduce PCom diameter. Our results suggest possible sources of variation of PComs in humans and provide information relevant when studying mouse models of occlusive cerebrovascular disease.

Placental growth factor deficiency is associated with impaired cerebral vascular development in mice

STUDY HYPOTHESIS

Placental growth factor (PGF) is expressed in the developing mouse brain and contributes to vascularization and vessel patterning.

STUDY FINDING

PGF is dynamically expressed in fetal mouse brain, particularly forebrain, and is essential for normal cerebrovascular development.

WHAT IS KNOWN ALREADY

PGF rises in maternal plasma over normal human and mouse pregnancy but is low in many women with the acute onset hypertensive syndrome, pre-eclampsia (PE). Little is known about the expression of PGF in the fetus during PE. Pgf  (-/-) mice appear normal but recently cerebral vascular defects were documented in adult Pgf  (-/-) mice.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Here, temporal-spatial expression of PGF is mapped in normal fetal mouse brains and cerebral vasculature development is compared between normal and congenic Pgf  (-/-) fetuses to assess the actions of PGF during cerebrovascular development. Pgf/PGF, Vegfa/VEGF, Vegf receptor (Vegfr)1 and Vegfr2 expression were examined in the brains of embryonic day (E)12.5, 14.5, 16.5 and 18.5 C57BL/6 (B6) mice using quantitative PCR and immunohistochemistry. The cerebral vasculature was compared between Pgf  (-/-) and B6 embryonic and adult brains using whole mount techniques. Vulnerability to cerebral ischemia was investigated using a left common carotid ligation assay.

MAIN RESULTS AND THE ROLE OF CHANCE

Pgf/PGF and Vegfr1 are highly expressed in E12.5-14.5 forebrain relative to VEGF and Vegfr2. Vegfa/VEGF is relatively more abundant in hindbrain (HB). PGF and VEGF expression were similar in midbrain. Delayed HB vascularization was seen at E10.5 and 11.5 in Pgf  (-/-) brains. At E14.5, Pgf  (-/-) circle of Willis showed unilateral hypoplasia and fewer collateral vessels, defects that persisted post-natally. Functionally, adult Pgf  (-/-) mice experienced cerebral ischemia after left common carotid arterial occlusion while B6 mice did not.

LIMITATIONS, REASONS FOR CAUTION

Since Pgf  (-/-) mice were used, consequences of complete absence of maternal and fetal PGF were defined. Therefore, the effects of maternal versus fetal PGF deficiency on cerebrovascular development cannot be separated. However, as PGF was strongly expressed in the developing brain at all timepoints, we suggest that local PGF has a more important role than distant maternal or placental sources. Full PGF loss is not expected in PE pregnancies, predicting that the effects of PGF deficiency identified in this model will be more severe than any effects in PE-offspring.

WIDER IMPLICATIONS OF THE FINDINGS

These studies provoke the question of whether PGF expression is decreased and cerebral vascular maldevelopment occurs in fetuses who experience a preeclamptic gestation. These individuals have already been reported to have elevated risk for stroke and cognitive impairments.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by awards from the Natural Sciences and Engineering Research Council, the Canada Research Chairs Program and the Canadian Foundation for Innovation to B.A.C. and by training awards from the Universidade Federal de Pernambuco and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Brazil to R.L.L.; Queen's University to V.R.K. and the Canadian Institutes of Health Research to M.T.R. The work of P.C. is supported by the Belgian Science Policy BELSPO-IUAP7/03, Structural funding by the Flemish Government-Methusalem funding, and the Flemish Science Fund-FWO grants. There were no competing interests.

Are parenchymal AVMs congenital lesions?

A long-held dogma in neurosurgery is that parenchymal arteriovenous malformations (AVMs) are congenital. However, there is no strong evidence supporting this theory. An increasing number of documented cases of de novo formation of parenchymal AVMs cast doubt on their congenital nature and suggest that indeed the majority of these lesions may form after birth. Further evidence suggesting the postnatal development of parenchymal AVMs comes from the exceedingly rare diagnosis of these lesions in utero despite the widespread availability of high-resolution imaging modalities such as ultrasound and fetal MRI. The exact mechanism of AVM formation has yet to be elucidated, but most likely involves genetic susceptibility and environmental triggering factors. In this review, the authors report 2 cases of de novo AVM formation and analyze the evidence suggesting that they represent an acquired condition.

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.

The Long and the Short of it: Gene and Environment Interactions During Early Cortical Development and Consequences for Long-Term Neurological Disease

Cortical development is a complex amalgamation of proliferation, migration, differentiation, and circuit formation. These processes follow defined timescales and are controlled by a combination of intrinsic and extrinsic factors. It is currently unclear how robust and flexible these processes are and whether the developing brain has the capacity to recover from disruptions. What is clear is that there are a number of cognitive disorders or conditions that are elicited as a result of disrupted cortical development, although it may take a long time for the full pathophysiology of the conditions to be realized clinically. The critical window for the manifestation of a neurodevelopmental disorder is prolonged, and there is the potential for a complex interplay between genes and environment. While there have been extended investigations into the genetic basis of a number of neurological and mental disorders, limited definitive associations have been discovered. Many environmental factors, including inflammation and stress, have been linked to neurodevelopmental disorders, and it may be that a better understanding of the interplay between genes and environment will speed progress in this field. In particular, the development of the brain needs to be considered in the context of the whole materno-fetal unit as the degree of the metabolic, endocrine, or inflammatory responses, for example, will greatly influence the environment in which the brain develops. This review will emphasize the importance of extending neurodevelopmental studies to the contribution of the placenta, vasculature, cerebrospinal fluid, and to maternal and fetal immune response. These combined investigations are more likely to reveal genetic and environmental factors that influence the different stages of neuronal development and potentially lead to the better understanding of the etiology of neurological and mental disorders such as autism, epilepsy, cerebral palsy, and schizophrenia.

Ethanol exposure during pregnancy persistently attenuates cranially directed blood flow in the developing fetus: evidence from ultrasound imaging in a murine second trimester equivalent model

BACKGROUND

Ethanol (EtOH) consumption during pregnancy can lead to fetal growth retardation, mental retardation, and neurodevelopmental delay. The fetal brain initiates neurogenesis and vasculogenesis during the second trimester, and depends on maternal-fetal circulation for nutrition and growth signals. We used high-resolution in vivo ultrasound imaging to test the hypothesis that EtOH interferes with fetal brain-directed blood flow during this critical developmental period.

METHODS

Pregnant mice were lightly anesthetized on gestational day 12 with an isoflurane/oxygen mixture. We assessed the effect of single and repeated binge-like maternal EtOH exposures at 3 g/kg, administered by intragastric gavage or intraperitoneal injection, on maternal circulation and fetal umbilical, aortic, internal carotid, and middle cerebral arterial circulation.

RESULTS

Binge maternal EtOH exposure, regardless of exposure route, significantly reduced fetal arterial blood acceleration and velocity time integral (VTI), from umbilical to cerebral arteries, without a change in fetal heart rate and resistivity indices. Importantly a single maternal binge EtOH exposure induced persistent suppression of fetal arterial VTI for at least 24 hours. Repeated binge episodes resulted in a continuing and persistent suppression of fetal VTI. Qualitative assessments showed that maternal EtOH exposure induced oscillatory, nondirectional blood flow in fetal cerebral arteries. Maternal cardiac and other physiological parameters remained unaltered.

CONCLUSIONS

These data show that binge-type maternal EtOH exposure results in rapid and persistent loss of blood flow from the umbilical artery to the fetal brain, potentially compromising nutrition and the maternal/fetal endocrine environment during a critical period for neuron formation and angiogenesis in the maturing brain.