The development of haemodynamics in the extracranial cerebral arteries of healthy preterm and term neonates

Normative and pathological values of hemodynamic and Doppler ultrasound arterial findings in children

Doppler ultrasound is an effective, useful and remarkably powerful tool in pediatric imaging. If possible, its use is always favored to avoid exposure to radiation or sedatives. By waveform spectrum analysis, Doppler ultrasound reveals information on blood flow and details on normal physiology and pathological processes undiscernible from gray-scale imaging alone. However, Doppler ultrasound remains underused, largely due to the difficult interpretation of changes in Doppler waveforms during childhood. This article provides a narrative review of the literature regarding the normative values and the physiological arterial changes through childhood according to age, weight or height, as well as frequent pathological arterial findings in children, classified by arterial territory.

Carotid foramen size in the human skull tracks developmental changes in cerebral blood flow and brain metabolism

OBJECTIVES

In humans, neuronal processes related to brain development elevate the metabolic rate of brain tissue relative to the body during early childhood. This phenomenon has been hypothesized to contribute to slow somatic growth in preadolescent Homo sapiens. The uncoupling of the brain's metabolic rate from brain size during development complicates the study of the evolutionary emergence of these traits in the fossil record. Here, we extend a method previously developed to predict interspecific differences in cerebral blood flow (a correlate of cerebral glucose use) to predict ontogenetic changes in human brain metabolism.

MATERIALS AND METHODS

Radii of the carotid foramen from an ontogenetic series of modern human crania were used to predict blood flow rates through the internal carotid arteries (ICA), which were compared to empirically measured ICA flow and brain metabolism values.

RESULTS

Predictions of both absolute ICA blood flow rates and perfusion (ICA blood flow rates relative to brain size) generally match measured values in infancy and childhood. Maximum predicted ICA blood flow rates and perfusion were found to occur between ages 5 and 8, which roughly correspond to the age of maximum measured ICA blood flow rate and absolute and brain mass-specific rate of whole brain glucose uptake.

DISCUSSION

These findings suggest that, during human growth and development, the size of the carotid foramen corresponds well to blood flow requirements through the ICA, and the method tested here may provide new opportunities for studying developmental changes in brain metabolism using osteological samples, including fossil hominins.

A longitudinal study of cerebral blood flow over the first 30 months

To investigate prospectively the development of cerebral perfusion during infancy, serial quantitative measurements of cerebral blood flow (CBF) volume were performed in two healthy children from birth up to the age of 30 mo. A total of 28 CBF volume measurements were done in either of the children. Absolute flows were measured in the internal carotid and vertebral arteries on both sides. Blood flow was calculated as the product of angle-corrected time-averaged flow velocity and the cross-sectional area of the vessel. Starting from 67 and 80 mL/min, respectively, at birth an almost 10-fold increase of CBF volume was observed in both children during the examination period. Half of this rise occurred during the first 6 mo, probably reflecting the steep metabolic incline during this period of synaptogenesis. The continuous increase in CBF volume after the sixth month of life mainly corresponds to brain growth. Estimated CBF (based on estimated brain weights) increased from 21 and 23 mL 100 g(-1) min(-1), respectively, after birth to 46 and 53 mL 100 g(-1) min(-1), respectively, during the first 6 mo of life in both children, remaining stable thereafter. This study is the first to provide longitudinal data of CBF during the first 30 mo after birth.

Normal Doppler spectral waveforms of major pediatric vessels: specific patterns

Every major vessel in the human body has a characteristic flow pattern that is visible in spectral waveforms obtained in that vessel with Doppler ultrasonography (US). Spectral waveforms reflect the physiologic status of the organ supplied by the vessel, as well as the anatomic location of the vessel in relation to the heart. In addition, the waveforms may be affected by age- and development-related hemodynamic differences. For example, adults tend to have higher flow velocities, whereas neonates, particularly those born prematurely, have higher resistance to flow, especially in the cerebral and renal vascular beds. As Doppler US is performed with increasing frequency for vascular evaluation in children, the recognition of normal flow patterns has become imperative. Familiarity with the waveforms characteristic of specific veins and arteries in children is important. In addition, an understanding of the hemodynamic factors involved provides a useful basis for interpreting waveform abnormalities.

Prenatal multicystic encephalomalacia due to anomaly of the aortic arch

Multicystic encephalomalacia (ME) usually results from severe hypoxic-ischemic brain damage occurring during the late third trimester of gestation and birth. We report on a case of congenital ME due to a congenital anomaly of the aortic origin of brachiocephalic vessels resulting in subclavian steal syndrome. A 5-day-old term neonate presented with microcephaly and overlapping cranial sutures. Both arms were developed normally. Magnetic resonance imaging of the brain showed extensive bilateral supratentorial ME. Color duplex sonography of the aortic arch and the intracranial and extracranial vessels revealed a stenosis at the origin of the left common carotid artery and atresia of the origin of the left subclavian artery resulting in left-sided subclavian steal syndrome and retrograde perfusion of the basilar artery. Total cerebral blood flow volume was reduced to 22 mL/min. Severely reduced cerebral blood flow volume resulted from left carotid artery stenosis and atresia of the origin of the left subclavian artery with consecutive subclavian steal. Infratentorial brain structures and the left arm remained intact, but supratentorial brain structures were severely affected with ME.

Noninvasive measurements of regional cerebral perfusion in preterm and term neonates by magnetic resonance arterial spin labeling

Magnetic resonance arterial spin labeling (ASL) at 3 Tesla has been investigated as a quantitative technique for measuring regional cerebral perfusion (RCP) in newborn infants. RCP values were measured in 49 healthy neonates: 32 preterm infants born before 34 wk of gestation and 17 term-born neonates. Examinations were performed on unsedated infants at postmenstrual age of 39-40 wk in both groups. Due to motion, reliable data were obtained from 23 preterm and 6 term infants. Perfusion in the basal ganglia (39 and 30 mL/100 g/min for preterm and term neonates, respectively) was significantly higher (p < 0.0001) than in cortical gray matter (19 and 16 mL/100 g/min) and white matter (15 and 10 mL/100 g/min), both in preterm neonates at term-equivalent age and in term neonates. Perfusion was significantly higher (p = 0.01) in the preterm group than in the term infants, indicating that RCP may be influenced by developmental and postnatal ages. This study demonstrates, for the first time, that noninvasive ASL at 3T may be used to measure RCP in healthy unsedated preterm and term neonates. ASL is, therefore, a viable tool that will allow serial studies of RCP in high-risk neonates.

The effect of preterm birth on neonatal cerebral vasculature studied with magnetic resonance angiography at 3 Tesla

Preterm birth is associated with a high incidence of neurodevelopmental deficits. Magnetic resonance imaging (MRI) has proved to be a valuable tool for monitoring development in the preterm brain. We used a dedicated time-of-flight (TOF) magnetic resonance angiography (MRA) protocol at 3 Tesla (3T) optimized to assess morphological characteristics of the neonatal cerebral vessels associated with preterm birth in a sample of 37 infants. We found statistically significant decreased tortuosity in all proximal segments of the cerebral vasculature (anterior, middle and posterior cerebral arteries) in the preterm infants imaged at term equivalent age compared to the term born infants, with no differences in vessel diameter between the two groups. This distinct phenotype of decreased tortuosity was shown to persist until 18 months of age in longitudinal MRA studies in infants born preterm, suggesting that this is not a delay in maturation. Biparietal head diameter measurements were significantly smaller in the preterm at term infants and were inversely correlated with middle cerebral artery tortuosity measurements in both the term born and the preterm at term infants. To our knowledge, this is the first systematic MRA study on the effect of preterm delivery on neonatal cerebral vasculature. Our intention is to build on the findings of this study by combining the data with other measurements of brain growth and vascular haemodynamics to understand more about the interdependence of vessel and brain development and their relationship to prematurity.

Magnetic Resonance Angiography of Cerebral Arteries After Neonatal Venoarterial and Venovenous Extracorporeal Membrane Oxygenation

Background and Purpose— In newborns with severe respiratory failure, extracorporeal membrane oxygenation (ECMO) has been proven to improve survival. With venoarterial ECMO, the right common carotid artery is ligated, whereas with venovenous ECMO, this carotid artery remains intact. The authors present the magnetic resonance angiography (MRA) evaluation of cerebral hemodynamics in a case of venoarterial and a case of venovenous ECMO.

Methods— With 2D phase-contrast MRA flow volume (mL/min), measurements are obtained of the brain feeding arteries and draining veins. Time-of-flight and flow-directional MRA are used to demonstrate the anatomy and flow patterns at the level of the circle of Willis.

Results– A total volume flow of 63 mL/min at the skull base and collateral flow via the anterior circle of Willis were measured in the infant after venoarterial ECMO, and a total volume flow of 86 mL/min and a fetal type configuration of the circle of Willis were observed in the infant after venovenous ECMO.

Conclusion— MRA is a useful technique to quantify cerebral blood flow in neonates after venoarterial or venovenous ECMO and could be used to select neonates with insufficient collateral compensation after venoarterial ECMO, requiring revascularization surgery.