A comparison of fetal organ measurements by echo-planar magnetic resonance imaging and ultrasound

Fetal Liver Volume Assessment Using Magnetic Resonance Imaging in Fetuses With Cytomegalovirus Infection†

Objective

To assess fetal liver volume (FLV) by magnetic resonance imaging (MRI) in cytomegalovirus (CMV)-infected fetuses compared to a group of healthy fetuses.

Method

Most infected cases were diagnosed by the evidence of ultrasound abnormalities during routine scans and in some after maternal CMV screening. CMV-infected fetuses were considered severely or mildly affected according to prenatal brain lesions identified by ultrasound (US)/MRI. We assessed FLV, the FLV to abdominal circumference (AC) ratio (FLV/AC-ratio), and the FLV to fetal body volume (FBV) ratio (FLV/FBV-ratio). As controls, we included 33 healthy fetuses. Hepatomegaly was evaluated post-mortem in 11 cases of congenital CMV infection. Parametric trend and intraclass correlation analyses were performed.

Results

There were no significant differences in FLV between infected (n = 32) and healthy fetuses. On correcting the FLV for AC and FBV, we observed a significantly higher FLV in CMV-infected fetuses. There were no significant differences in the FLV, or the FLV/AC or FLV/FBV-ratios according to the severity of brain abnormalities. There was excellent concordance between the fetal liver weight estimated by MRI and liver weight obtained post-mortem. Hepatomegaly was not detected in any CMV-infected fetus.

Conclusion

In CMV-infected fetuses, FLV corrected for AC and FBV was higher compared to healthy controls, indicating relative hepatomegaly. These parameters could potentially be used as surrogate markers of liver enlargement.

Measurement of the Brain Volume/Liver Volume Ratio by Three-Dimensional MRI in Appropriate-for-Gestational Age Fetuses and Those With Fetal Growth Restriction

BACKGROUND

Fetal growth restriction (FGR) is associated with a high fetal brain volume/liver volume (FBV/FLV) ratio. Ultrasound may not always be reliable, which has prompted further investigation of MRI techniques.

PURPOSE

To determine the relationship between FBV/FLV ratio, as measured by MRI, and gestational age (GA) in normal fetuses and those with FGR.

STUDY TYPE

Retrospective.

POPULATION

One hundred and forty seven singleton pregnancies including 105 appropriate-for-gestational age (AGA) fetuses and 42 FGR fetuses.

FIELD STRENGTH/SEQUENCE

Three-dimensional fast imaging employing steady-state acquisition at 1.5 T.

ASSESSMENT

The FBV and FLV were measured by three radiologists. The inter- and intraobserver agreements, the correlation between FBV/FLV ratio, and advancing GA were evaluated; the diagnostic value of FBV/FLV ratio was evaluated and compared with head circumference/abdominal circumference (HC/AC) ratio measured by ultrasound.

STATISTICAL TESTS

Intraclass correlation coefficient (ICC) was used to determine inter- and intraobserver agreements. Regression analysis was used to assess the correlation between FBV/FLV ratio and advancing GA. The diagnostic value of the FBV/FLV ratio was examined by the area under the receiver operating characteristic (ROC) curve.

RESULTS

The inter- and intraobserver agreements were excellent with an interobserver ICC of 0.984 and intra-observer ICCs of 0.989, 0.994, and 0.995. The FBV/FLV ratio in AGA fetuses decreased significantly with advancing GA (Pearson correlation coefficient = -0.844). The FBV/FLV ratio in FGR fetuses was significantly higher than that in AGA fetuses. To identify fetuses at high risk for FGR using the FBV/FLV ratio, the area under the ROC curve was 0.978, with an optimal cut-off value of 4.10. The sensitivity of FBV/FLV ratio in identifying FGR was significantly higher than that of HC/AC ratio (0.929 vs. 0.529).

DATA CONCLUSION

An inverse correlation exists between FBV/FLV ratio and advancing GA in normal fetuses. A high FBV/FLV ratio may be used to ascertain fetuses at high risk for FGR.

LEVEL OF EVIDENCE

3 Technical Efficacy Stage: 3.

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on the Growth and Composition of Fetal Organs

BACKGROUND

The growth of fetal organs is a dynamic process involving considerable changes in the anatomical and physiological parameters that can alter fetal exposure to xenobiotics in utero. Physiologically based pharmacokinetic models can be used to predict the fetal exposure as time-varying parameters can easily be incorporated.

OBJECTIVE

The objective of this study was to collate, analyse and integrate the available time-varying parameters needed for the physiologically based pharmacokinetic modelling of xenobiotic kinetics in a fetal population.

METHODS

We performed a comprehensive literature search on the physiological development of fetal organs. Data were carefully assessed, integrated and a meta-analysis was performed to establish growth trends with fetal age and weight. Algorithms and models were generated to describe the growth of these parameter values as functions of age and/or weight.

RESULTS

Fetal physiologically based pharmacokinetic parameters, including the size of the heart, liver, brain, kidneys, lungs, spleen, muscles, pancreas, skin, bones, adrenal and thyroid glands, thymus, gut and gonads were quantified as a function of fetal age and weight. Variability around the means of these parameters at different fetal ages was also reported. The growth of the investigated parameters was not consistent (with respect to direction and monotonicity).

CONCLUSION

Despite the limitations identified in the availability of some values, the data presented in this article provide a unique resource for age-dependent organ size and composition parameters needed for fetal physiologically based pharmacokinetic modelling. This will facilitate the application of physiologically based pharmacokinetic models during drug development and in the risk assessment of environmental chemicals and following maternally administered drugs or unintended exposure to environmental toxicants in this population.

Growth of the colon and rectum throughout gestation: evaluation with fetal MRI

Background

Congenital abnormalities of the gastrointestinal tract are increasingly being evaluated by prenatal magnetic resonance imaging (MRI). However, there is a paucity of reports describing the normal quantitative development of the fetal colon and rectum on MRI.

Purpose

To provide growth curves of the MRI estimated diameter of the fetal colon and rectum as a function of gestational age.

Material and Methods

This is a retrospective review of 191 singleton fetal MRI studies at 25–39 weeks of gestation. Measurements included maximal diameter of the ascending, transverse, and descending colon on coronal and sagittal views, maximal diameter of the rectum on coronal and sagittal views, and maximal diameter of the rectum at the level of the bladder base on sagittal views. Median growth curves were built using a generalized additive model. Confidence regions were built for 10th, 25th, 75th, and 90th percentiles.

Results

Smoothed growth curves for the median, and one and three quartiles for each of the five sections as a function of gestational age were calculated. All graphs had a slightly exponential curve.

Conclusion

This study provides normal ranges of the prenatal colon and rectum as a function of gestational age. They may serve as reference values when interpreting fetal MRI.

Hepato - Cephalic Index as a Predictor of Intrauterine Growth Restriction

Aim:

The aims of this study were to compare ultrasound fetoplacental parameters and to calculate Hepato-Cephalic Index (HCI) as a new predictor of IUGR.

Methods and material:

A clinical prospective study was conducted and included 120 pregnant women divided in two groups: non IUGR group included healthy pregnant women (n=60) and IUGR group included pregnant women with preeclampsia and IUGR (n=60). Outcome measures were following ultrasound fetoplacental parameters in fetuses with IUGR and non IUGR: Fetal Liver Length (FLL), Femur Length (FL), Biparietal Diameter (BPD), Placental Maturation by Grannum, Amniotic Fluid Index (AFI) and Hepato-Cephalic Index (HCI). Sonography was carried out by probe 3.5 Mhz type MINDRAY DC 7.

Results:

The mean of maternal age was 30.0±6.1 years in women with preeclampsia and IUGR and 28.1±5.1 years in healthy pregnant women, p > 0.05. There was a statistically significant difference in values of: FLL (p < 0.001), FL (p = 0.004), BPD (p < 0.001), AFI (p < 0.001), HCI (p < 0.001) between IUGR and non IUGR groups. The most of women with preeclampsia and IUGR had grade III of placental maturation (48.3%). There is a significant association between the placental maturation and the diagnosis, p < 0.001. There was a statistically significant difference in body mass of newborns between IUGR and non IUGR groups, p < 0.001.

Conclusion:

In a fetus with IUGR in preeclampsia there is a reduction in FLL, FL, BPD, AFI and HCI and there is a early maturation of the placenta. By measurement of fetoplacental ultrasonic parameters of liver, pregnant women will experience prediction of risk pregnancy (preeclampsia with IUGR) due to hypoxia.

Volumetric Growth of the Liver in the Human Fetus: An Anatomical, Hydrostatic, and Statistical Study

Using anatomical, hydrostatic, and statistical methods, liver volumes were assessed in 69 human fetuses of both sexes aged 18-30 weeks. No sex differences were found. The median of liver volume achieved by hydrostatic measurements increased from 6.57 cm(3) at 18-21 weeks through 14.36 cm(3) at 22-25 weeks to 20.77 cm(3) at 26-30 weeks, according to the following regression: y = -26.95 + 1.74 × age ± Z × (-3.15 + 0.27 × age). The median of liver volume calculated indirectly according to the formula liver volume = 0.55 × liver length × liver transverse diameter × liver sagittal diameter increased from 12.41 cm(3) at 18-21 weeks through 28.21 cm(3) at 22-25 weeks to 49.69 cm(3) at 26-30 weeks. There was a strong relationship (r = 0.91, p < 0.001) between the liver volumes achieved by hydrostatic (x) and indirect (y) methods, expressed by y = -0.05 + 2.16x ± 7.26. The liver volume should be calculated as follows liver volume = 0.26 × liver length × liver transverse diameter × liver sagittal diameter. The age-specific liver volumes are of great relevance in the evaluation of the normal hepatic growth and the early diagnosis of fetal micro- and macrosomias.

Fetal Growth and Neurodevelopmental Outcome in Congenital Heart Disease

We evaluated differences in growth between fetuses with and without congenital heart disease (CHD) and tested associations between growth and early childhood neurodevelopment (ND). In this prospective cohort study, fetuses with hypoplastic left heart syndrome (HLHS), transposition of the great arteries (TGA), and tetralogy of Fallot (TOF) and controls had biparietal diameter (BPD), head (HC) and abdominal circumference (AC), femur length (FL), and estimated fetal weight (EFW) recorded serially during pregnancy at 18-26 weeks GA (F1), at 27-33 weeks GA (F2), and at 34-40 weeks GA (F3). CHD subjects underwent Bayley Scales of Infant Development-III ND testing at 18 months. Differences between CHD fetuses and controls were assessed using t tests and generalized linear modeling. Correlations between biometry and ND informed regression modeling. We enrolled 41 controls and 68 fetuses with CHD (N = 24 HLHS, N = 21 TGA, N = 23 TOF), 46 of whom had ND scores available. At 18-26 weeks, CHD fetuses were smaller than controls in all biometric parameters. Differences in growth rates were observed for HC, BPD, and AC, but not for FL or EFW. Cognitive score correlated with HC/AC at F2 (r = -0.33, P = 0.04) and mean HC/AC across gestation (r = -0.35, P = 0.03). Language correlated with FL/BPD at F2 (r = 0.34, P = 0.04). In stepwise linear regression, mean HC/AC predicted Cognition (B = -102, P = 0.026, R (2) = 0.13) and FL/BPD at F2 predicted Language score (B = 127, P = 0.03, R (2) = 0.12). Differences in growth between CHD fetuses and controls can be measured early in pregnancy. In CHD fetuses, larger abdominal relative to head circumference is associated with better 18-month neurodevelopment.

Morphology and morphometry of fetal liver at 16-26 weeks of gestation by magnetic resonance imaging: Comparison with embryonic liver at Carnegie stage 23

AIM

Normal liver growth was described morphologically and morphometrically using magnetic resonance imaging (MRI) data of human fetuses, and compared with embryonic liver to establish a normal reference chart for clinical use.

METHODS

MRI images from 21 fetuses at 16-26 weeks of gestation and eight embryos at Carnegie stage (CS)23 were investigated in the present study. Using the image data, the morphology of the liver as well as its adjacent organs was extracted and reconstructed three-dimensionally. Morphometry of fetal liver growth was performed using simple regression analysis.

RESULTS

The fundamental morphology was similar in all cases of the fetal livers examined. The liver tended to grow along the transversal axis. The four lobes were clearly recognizable in the fetal liver but not in the embryonic liver. The length of the liver along the three axes, liver volume and four lobes correlated with the bodyweight (BW). The morphogenesis of the fetal liver on the dorsal and caudal sides was affected by the growth of the abdominal organs, such as the stomach, duodenum and spleen, and retroperitoneal organs, such as the right adrenal gland and right kidney. The main blood vessels such as inferior vena cava, portal vein and umbilical vein made a groove on the surface of the liver. Morphology of the fetal liver was different from that of the embryonic liver at CS23.

CONCLUSION

The present data will be useful for evaluating the development of the fetal liver and the adjacent organs that affect its morphology.

Isoflurane/nitrous oxide anesthesia and stress-induced procedures enhance neuroapoptosis in intrauterine growth-restricted piglets

PURPOSE

There is compelling evidence that interference of various anesthetics with synaptic functions and stress-provoking procedures during critical periods of brain maturation results in increased neuroapoptotic cell death. The hypothesis is that adverse intrauterine environmental conditions leading to intrauterine growth restriction (IUGR) with altered brain development may result in enhanced susceptibility to developmental anesthetic neurotoxicity.

METHODS

This was a prospective, randomized, blinded animal study performed in a university laboratory involving 20 normal-weight (NW) and 19 IUGR newborn piglets. General inhalation anesthesia with isoflurane and nitrous oxide at clinically comparable dosages were administered for about 10 h. Surgical and monitoring procedures were accompanied by appropriate stage of general anesthesia. Resulting effects on developmental anesthetic and stress-induced neurotoxicity were assessed by estimation of apoptotic rates in untreated piglets and piglets after 10-h general anesthesia with MAC 1.0 isoflurane in 70 % nitrous oxide and 30 % oxygen.

RESULTS

IUGR piglets exposed to different levels of isoflurane inhalation exhibited a significant increased apoptosis rate (TUNEL-positive neuronal cells) compared to NW animals of similar condition (P < 0.05). Cardiovascular and metabolic monitorings revealed similar effects of general anesthesia together with similar effects on brain electrical activity and broadly a similar dose-dependent gradual restriction in brain oxidative metabolism in NW and IUGR piglets.

CONCLUSIONS

There is no indication that the increased rate in neuroapoptosis in IUGR piglets is confounded by additional adverse systemic or organ-specific impairments resulting from administered mixed inhalation anesthesia. Developmental anesthetic and stress-induced neuroapoptosis presumably originated in response to fetal adaptations to adverse conditions during prenatal life and should be considered in clinical interventions on infants having suffered from fetal growth restriction.

eNOS knockout mouse as a model of fetal growth restriction with an impaired uterine artery function and placental transport phenotype

Fetal growth restriction (FGR) is the inability of a fetus to reach its genetically predetermined growth potential. In the absence of a genetic anomaly or maternal undernutrition, FGR is attributable to "placental insufficiency": inappropriate maternal/fetal blood flow, reduced nutrient transport or morphological abnormalities of the placenta (e.g., altered barrier thickness). It is not known whether these diverse factors act singly, or in combination, having additive effects that may lead to greater FGR severity. We suggest that multiplicity of such dysfunction might underlie the diverse FGR phenotypes seen in humans. Pregnant endothelial nitric oxide synthase knockout (eNOS(-/-)) dams exhibit dysregulated vascular adaptations to pregnancy, and eNOS(-/-) fetuses of such dams display FGR. We investigated the hypothesis that both altered vascular function and placental nutrient transport contribute to the FGR phenotype. eNOS(-/-) dams were hypertensive prior to and during pregnancy and at embryonic day (E) 18.5 were proteinuric. Isolated uterine artery constriction was significantly increased, and endothelium-dependent relaxation significantly reduced, compared with wild-type (WT) mice. eNOS(-/-) fetal weight and abdominal circumference were significantly reduced compared with WT. Unidirectional maternofetal (14)C-methylaminoisobutyric acid (MeAIB) clearance and sodium-dependent (14)C-MeAIB uptake into mouse placental vesicles were both significantly lower in eNOS(-/-) fetuses, indicating diminished placental nutrient transport. eNOS(-/-) mouse placentas demonstrated increased hypoxia at E17.5, with elevated superoxide compared with WT. We propose that aberrant uterine artery reactivity in eNOS(-/-) mice promotes placental hypoxia with free radical formation, reducing placental nutrient transport capacity and fetal growth. We further postulate that this mouse model demonstrates "uteroplacental hypoxia," providing a new framework for understanding the etiology of FGR in human pregnancy.

Foetal volumetry using magnetic resonance imaging in intrauterine growth restriction

OBJECTIVES

We used magnetic resonance imaging (MRI) to perform volumetry of foetuses with and without growth restriction, and identify deviations in organ growth.

STUDY DESIGN

20 growth restricted and 19 normal foetuses were scanned once during pregnancy at gestational age 20.53-36.57 weeks. MRI scans were performed on a 1.5T system using ssFSE sequences. Manual segmentation of whole body, brain, heart, lung, liver, thymus and kidney volume was performed. Data on the severity of foetal growth restriction and pregnancy outcome was collected.

RESULTS

There was a significant reduction in foetal whole body volume and volume of all internal organs except the brain in growth restricted foetuses. A brain:liver ratio above 3.0 was associated with a 3.3 fold increase in risk of perinatal mortality (95% CI=1.68-6.47).

CONCLUSION

MRI provides an accurate assessment of foetal organ growth. It may have a role to play in monitoring disease severity and the effect of future interventions.

Comparison of measurements of the transverse diameter and perimeter of the fetal thymus obtained by magnetic resonance and ultrasound imaging

PURPOSE

To compare measurements of the fetal thymus obtained by magnetic resonance imaging (MRI) and ultrasound (US).

MATERIALS AND METHODS

Written informed consent was obtained from the patients that participated in this Institutional Review Board-approved observational study. The study population consisted of 17 pregnant women carrying fetuses between 21 and 34 weeks of gestation with suspected abnormalities. The transverse diameter and perimeter of the thymus were measured in these fetuses at the level of an axial view of the thorax that includes the pulmonary, aorta, and superior vena cava. The degree of agreement between MRI and US measurements was determined using Lin's concordance correlation coefficient and Bland-Altman analysis.

RESULTS

The mean (standard deviation, SD) gestational age at the time of the prenatal evaluation was 28.4 weeks (3.6). The thymus was measured by MRI and US in all cases. Comparison of the measurements from these two imaging modalities demonstrated a relatively good reproducibility with no evidence of systematic error.

CONCLUSION

MRI and US measurements of the fetal thymus during the second half of pregnancy are comparable. This finding suggests that MRI can become a useful adjuvant to US for assessment of the fetal thymus.

Ovine surgical model of uterine space restriction: interactive effects of uterine anomalies and multifetal gestations on fetal and placental growth

Intrauterine growth restriction (IUGR) is observed in conditions with limitations in uterine space (e.g., uterine anomalies and multifetal gestations). IUGR is associated with reduced fetal weight, organ growth, and a spectrum of adult-onset diseases. To examine the interaction of uterine anomalies and multifetal gestations, we developed a surgical uterine space restriction model with a unilateral uterine horn ligation before breeding (unilateral surgery). Placentas and fetuses were studied on Gestational Day (GD) 120 and GD 130 (term = 147 days). Unilateral surgery decreased placentome numbers in singleton and twin pregnancies (25% and 50%, respectively) but not unilateral triplets. Unilateral surgery decreased total placentome weight in twin pregnancies (decreased 24%). Fetuses categorized as uterine space restricted (unilateral twin and both groups of triplets) had 51% fewer placentomes per fetus and a 31% reduction in placentomal weight per fetus compared to the nonrestricted group (control singleton, unilateral singleton, and control twin). By GD 130, uterine space-restricted fetuses exhibited decreased weight, smaller crown-rump, abdominal girth, and thoracic girth as well as decreased fetal heart, kidney, liver, spleen, and thymus weights. Lung and brain weights were unaffected, demonstrating asymmetric IUGR. At GD 130, placental efficiency (fetal weight per total placentomal weight) was elevated in uterine space-restricted fetuses. However, fetal arterial creatinine, blood urea nitrogen, and cholesterol were elevated, suggesting insufficient placental clearance. Maternal-to-fetal glucose and triglycerides ratios were elevated in the uterine space-restricted pregnancies, suggesting placental nutrient transport insufficiency. This model allows for examination of interactive effects of uterine space restriction-induced IUGR on placental adaptation and fetal organ growth.

Fetal programming of infant neuromotor development: the generation R study

The objective of the study was to examine whether infant neuromotor development is determined by fetal size and body symmetry in the general population. This study was embedded within the Generation R Study, a population-based cohort in Rotterdam. In 2965 fetuses, growth parameters were measured in mid-pregnancy and late pregnancy. After birth, at age 9 to 15 wks, neuromotor development was assessed with an adapted version of Touwen's Neurodevelopmental Examination. Less optimal neuromotor development was defined as a score in the highest tertile. We found that higher fetal weight was beneficial to infant neurodevelopment. A fetus with a 1-SD score higher weight in mid-pregnancy had an 11% lower risk of less optimal neuromotor development (OR: 0.89; 95% CI: 0.82-0.97). Similarly, a fetus with a 1-SD score larger abdominal-to-head circumference (AC/HC) ratio had a 13% lower risk of less optimal neuromotor development (OR: 0.87; 95% CI: 0.79-0.96). These associations were also present in late pregnancy. Our findings show that fetal size and body symmetry in pregnancy are associated with infant neuromotor development. These results suggest that differences in infant neuromotor development, a marker of behavioral and cognitive problems, are at least partly caused by processes occurring early in fetal life.

Three-dimensional sonographic calculation of the volume of intracranial structures in growth-restricted and appropriate-for-gestational age fetuses

OBJECTIVES

To evaluate the feasibility and reproducibility of volume segmentation of fetal intracranial structures using three-dimensional (3D) ultrasound imaging, and to estimate differences in the volume of intracranial structures between intrauterine growth-restricted (IUGR) and appropriate-for-gestational age (AGA) fetuses.

METHODS

Total intracranial, frontal, thalamic and cerebellar volumes were measured using 3D ultrasound imaging and Virtual Organ Computer-aided AnaLysis (VOCAL) in 39 IUGR and 39 AGA fetuses matched for gestational age, at 28-34 weeks of gestation. Volumes of, and ratios between, structures were estimated, and differences between IUGR and AGA fetuses were calculated. Volume measurements were performed by two observers, and interobserver and intraobserver intraclass correlation coefficients (ICCs) were calculated for each structure.

RESULTS

Volumes were satisfactorily obtained in all fetuses. All net volumes except those for the thalamus (P = 0.23) were significantly smaller (P = 0.001) in IUGR fetuses. After adjusting volumes for biparietal diameter the frontal volume was significantly smaller (P = 0.02) and the thalamic volume significantly greater (P = 0.03) in IUGR fetuses than in AGA fetuses. Significant intergroup differences in the ratios between structures were found only in those involving the frontal region. Interobserver ICCs were as follows: total intracranial 0.97 (95% CI, 0.92-0.98), cerebellar 0.69 (95% CI, 0.44-0.75), frontal 0.66 (95% CI, 0.42-0.79) and thalamic 0.54 (95% CI, 0.37-0.72).

CONCLUSIONS

IUGR fetuses show differences in the volume of intracranial structures compared with AGA fetuses, with the largest difference found in the frontal region. These differences might be explained by in-utero processes of neural reorganization induced by chronic hypoxia.

Comparison of fetal biometric values with sonographic and 3D reconstruction MRI in term gestations

OBJECTIVE

We sought to compare the fetal biometric values head and abdominal circumferences, biparietal and occipital-frontal diameters, and left and right ventricular atrial diameters obtained with contemporaneous sonography and 3D MRI reconstructions in term pregnancies.

SUBJECTS AND METHODS

A total of 107 nulliparous women evaluated as having uncomplicated pregnancies and scheduled for induction at 42 completed weeks gave their informed consent and underwent MRI and sonography within 3 hours of each other. Two single-shot fast spin-echo MRI sequences were performed with 7- and 4-mm slice thicknesses and no gap. A single observer performed MRI postprocessing to obtain biometric values. A single sonographer using a 3- to 5-MHz curvilinear transducer performed transabdominal sonography. Concordance correlation and Bland-Altman analysis of differences were performed.

RESULTS

Concordance correlation was poor for both right (0.024) and left (0.005) ventricular atrial diameters. There were moderate concordance correlations for head (0.56) and abdominal (0.53) circumferences and biparietal diameter (0.61). Occipital-frontal diameter had fair correlation (0.27).

CONCLUSION

Comparison between contemporaneous sonographic and 3D reconstructed MR images at late gestational ages shows acceptable correlation between the two techniques for head circumference, abdominal circumference, and biparietal diameter.

MR imaging methods for assessing fetal brain development

Fetal magnetic resonance imaging provides an ideal tool for investigating growth and development of the brain in vivo. Current imaging methods have been hampered by fetal motion but recent advances in image acquisition can produce high signal to noise, high resolution 3-dimensional datasets suitable for objective quantification by state of the art post acquisition computer programs. Continuing development of imaging techniques will allow a unique insight into the developing brain, more specifically process of cell migration, axonal pathway formation, and cortical maturation. Accurate quantification of these developmental processes in the normal fetus will allow us to identify subtle deviations from normal during the second and third trimester of pregnancy either in the compromised fetus or in infants born prematurely.

Postmortem fetal organ volumetry using magnetic resonance imaging and comparison to organ weights at conventional autopsy

OBJECTIVES

Following perinatal death, organ weights at autopsy may provide evidence of growth restriction and pulmonary hypoplasia. Whilst postmortem magnetic resonance imaging (MRI) may provide comparable information to autopsy about structural abnormalities, its ability to provide reproducible data about organ size has yet to be determined. We examined the feasibility of using postmortem MRI to provide estimates of organ size and weight.

METHODS

Twenty-five fetuses of gestational age from 16 to 40 weeks underwent postmortem MRI prior to autopsy. Fetal lung, brain and liver volume estimations were performed by two observers using the stereology technique on postmortem MRI slices. Fetal lung, brain and liver weights were recorded at autopsy. Organ volume estimates and autopsy organ weights were compared using regression analysis, and estimates of fetal organ densities made. Interobserver variability was assessed using a Bland-Altman plot. Receiver-operating characteristics curve (ROC) analysis compared MRI brain : liver volume ratios to autopsy brain : liver weight ratios.

RESULTS

A linear relationship between organ volume estimates and organ weight was observed. Estimated densities for the fetal brain, liver and lung were 1.08 g/cm(3), 1.15 g/cm(3) and 1.15 g/cm(3), respectively. Interobserver 5th and 95th percentile limits of agreement for fetal brain, liver and lung were - 5.4% to + 7.9%, - 11.8% to + 8.3% and - 14.3% to + 8.7%, respectively. For MRI organ volumes to detect a brain weight : liver weight ratio > or = 4, ROC analysis demonstrated an area under the curve of 0.61, with an optimal cut-off of 4.1.

CONCLUSION

Postmortem MRI organ volumetry can be used to estimate weights of major fetal organs. This may increase the information obtained from a minimally-invasive perinatal autopsy, particularly in the context of pulmonary hypoplasia and intrauterine growth restriction, where differential organ growth plays a major part in assessment of the underlying pathology.

Investigation of normal organ development with fetal MRI

The understanding of the presentation of normal organ development on fetal MRI forms the basis for recognition of pathological states. During the second and third trimesters, maturational processes include changes in size, shape and signal intensities of organs. Visualization of these developmental processes requires tailored MR protocols. Further prerequisites for recognition of normal maturational states are unequivocal intrauterine orientation with respect to left and right body halves, fetal proportions, and knowledge about the MR presentation of extrafetal/intrauterine organs. Emphasis is laid on the demonstration of normal MR appearance of organs that are frequently involved in malformation syndromes. In addition, examples of time-dependent contrast enhancement of intrauterine structures are given.

Antenatal magnetic resonance imaging is useful in providing predictive values for surgical procedures in abdominal wall defects

BACKGROUND

Antenatal magnetic resonance imaging (MRI) is useful for the diagnosis of abdominal wall defects. Its predictive value concerning the possibility of primary closure of the abdominal wall, however, has so far not been reported.

METHODS

Between August 2001 and November 2004, antenatal MRI was performed on 9 patients with abdominal wall defects in whom surgical repair was performed immediately after birth. Areas of the abdominal cavity and exteriorized viscera were manually traced from both sagittal and axial MR images, and the data were further transmitted to a Workstation for MRI Volumetry (Advantage Windows 4.1, General Electric Medical Systems, Milwaukee, Wis). We examined the exteriorized ratio (ER), which is calculated by dividing the absolute volume of the abdominal cavity by that of the exteriorized viscera, and evaluated the predictive value by a retrospective comparison with surgical procedure.

RESULTS

In the primary closure group (n = 5), mean values of ER were 0.33 +/- 0.31 from axial and 0.45 +/- 0.31 from sagittal MR images. In contrast, in the staged closure group (n = 4), mean values of ER were 1.39 +/- 0.40 from axial and 1.34 +/- 0.42 from sagittal MR images. There was a significant difference (P < .05) between the 2 groups for both sets of images. The ER obtained from antenatal MRI correlated well with surgical procedure.

CONCLUSIONS

The ER might be useful for antenatal counseling, planning for delivery, and prediction of the most likely surgical procedure.

Regional brain development in serial magnetic resonance imaging of low-risk preterm infants

OBJECTIVE

MRI studies have shown that preterm infants with brain injury have altered brain tissue volumes. Investigation of preterm infants without brain injury offers the opportunity to define the influence of early birth on brain development and provide normative data to assess effects of adverse conditions on the preterm brain. In this study, we investigated serial MRI of low-risk preterm infants with the aim to identify regions of altered brain development.

METHODS

Twenty-three preterm infants appropriate for gestational age without magnetic resonance-visible brain injury underwent MRI twice at 32 and at 42 weeks' postmenstrual age. Fifteen term infants were scanned 2 weeks after birth. Brain tissue classification and parcellation were conducted to allow comparison of regional brain tissue volumes. Longitudinal brain growth was assessed from preterm infants' serial scans.

RESULTS

At 42 weeks' postmenstrual age, gray matter volumes were not different between preterm and term infants. Myelinated white matter was decreased, as were unmyelinated white matter volumes in the region including the central gyri. The gray matter proportion of the brain parenchyma constituted 30% and 37% at 32 and 42 weeks' postmenstrual age, respectively.

CONCLUSIONS

This MRI study of preterm infants appropriate for gestational age and without brain injury establishes the influence of early birth on brain development. No decreased cortical gray matter volumes were found, which is in contrast to findings in preterm infants with brain injury. Moderately decreased white matter volumes suggest an adverse influence of early birth on white matter development. We identified a sharp increase in cortical gray matter volume in preterm infants' serial data, which may correspond to a critical period for cortical development.

Birth characteristics and risk of low intellectual performance in early adulthood: are the associations confounded by socioeconomic factors in adolescence or familial effects?

OBJECTIVE

In this study we investigated whether the association between measures of fetal growth restriction and intellectual performance was mediated by socioeconomic or familial factors.

METHODS

This was a population-based cohort study of 357,768 Swedish males born as singletons without congenital malformations between 1973 and 1981. The main outcome measure was intellectual performance at military conscription.

RESULTS

Compared with men born with appropriate birth weight for gestational age, men born light for gestational age suffered an increased risk of low intellectual performance after adjustment for maternal and socioeconomic factors. The increase in risk of low intellectual performance related to a decrease in birth weight for gestational age was similar between families and within families. Men born short or with a small head circumference for gestational age were also at increased risk of low intellectual performance, both when adjusting for maternal and socioeconomic factors and within families.

CONCLUSIONS

We found that all of the studied dimensions of restricted fetal growth are independently associated with increased risks of low intellectual performance and that these associations are only partly mediated by socioeconomic or familial factors.

Fetal abdominal magnetic resonance imaging

This review deals with the in vivo magnetic resonance imaging (MRI) appearance of the human fetal abdomen. Imaging findings are correlated with current knowledge of human fetal anatomy and physiology, which are crucial to understand and interpret fetal abdominal MRI scans. As fetal MRI covers a period of more than 20 weeks, which is characterized not only by organ growth, but also by changes and maturation of organ function, a different MR appearance of the fetal abdomen results. This not only applies to the fetal intestines, but also to the fetal liver, spleen, and adrenal glands. Choosing the appropriate sequences, various aspects of age-related and organ-specific function can be visualized with fetal MRI, as these are mirrored by changes in signal intensities. Knowledge of normal development is essential to delineate normal from pathological findings in the respective developmental stages.