Normal human brainstem development in vivo: a quantitative fetal MRI study

Standardised and structured reporting in fetal magnetic resonance imaging: recommendations from the Fetal Task Force of the European Society of Paediatric Radiology

Over the last decades, magnetic resonance imaging (MRI) has emerged as a valuable adjunct to prenatal ultrasound for evaluating fetal malformations. Several radiological societies advocate for standardised and structured reporting practices to enhance the uniformity of imaging language. Compared to narrative formats, standardised and structured reports offer enhanced content quality, minimise reader variability, have the potential to save reporting time, and streamline the communication between specialists by employing a shared lexicon. Structured reporting holds promise for mitigating medico-legal liability, while also facilitating rigorous scientific data analyses and the development of standardised databases. While structured reporting templates for fetal MRI are already in use in some centres, specific recommendations and/or guidelines from international societies are scarce in the literature. The purpose of this paper is to propose a standardised and structured reporting template for fetal MRI to assist radiologists, particularly those with less experience, in delivering systematic reports. Additionally, the paper aims to offer an overview of the anatomical structures that necessitate reporting and the prevalent normative values for fetal biometrics found in current literature.

Associations and outcomes of prenatally detected rhombencephalosynapsis

OBJECTIVE

To describe the association between prenatal imaging and neurodevelopmental outcomes of fetuses with rhombencephalosynapsis (RES).

STUDY DESIGN

Thirty-four pregnancies complicated by RES were identified from our institutional databases based on US and/or MRI findings. Genetic testing results were gathered. In cases of termination of pregnancy, we studied the association between prenatal imaging and neuropathologic findings. For those who opted for expectant management, comprehensive developmental assessments and postnatal MRI imaging were evaluated.

RESULTS

Over one third of fetuses in our cohort had complete RES. Common intracranial anomalies identified were mesencephalosynapsis, aqueduct stenosis and diencephalosynapsis. The degree of RES was not associated with the frequency of additional central nervous system anomalies. MRI had a good correlation with neuropathologic findings with regard to the degree of RES, aqueduct stenosis and mesencephalosynapsis. Postmortem autopsy showed that one third of our cases had VACTERL-H and almost all of those had complete RES. All liveborn neonates(n = 6) had aqueduct stenosis requiring ventriculoperitoneal shunting within days of delivery (median 5 days). While a large proportion of prenatally suspected complete RES were found to have partial RES on postnatal imaging, prenatal diagnosis of aqueduct stenosis remained unchanged. All children that were at least 2 years old (n = 3) had global developmental delay.

CONCLUSION

Prenatal assessment of the RES severity is challenging and may be unreliable. Nevertheless, postnatal prognosis is poor for both complete and partial RES. Associated aqueductal stenosis, can be reliably assessed prenatally and this may contribute to worse postnatal prognosis than the degree of RES.

Experience of early-life pain in premature infants is associated with atypical cerebellar development and later neurodevelopmental deficits

BACKGROUND

Infants born very and extremely premature (V/EPT) are at a significantly elevated risk for neurodevelopmental disorders and delays even in the absence of structural brain injuries. These risks may be due to earlier-than-typical exposure to the extrauterine environment, and its bright lights, loud noises, and exposures to painful procedures. Given the relative underdeveloped pain modulatory responses in these infants, frequent pain exposures may confer risk for later deficits.

METHODS

Resting-state fMRI scans were collected at term equivalent age from 148 (45% male) infants born V/EPT and 99 infants (56% male) born at term age. Functional connectivity analyses were performed between functional regions correlating connectivity to the number of painful skin break procedures in the NICU, including heel lances, venipunctures, and IV placements. Subsequently, preterm infants returned at 18 months, for neurodevelopmental follow-up and completed assessments for autism risk and general neurodevelopment.

RESULTS

We observed that V/EPT infants exhibit pronounced hyperconnectivity within the cerebellum and between the cerebellum and both limbic and paralimbic regions correlating with the number of skin break procedures. Moreover, skin breaks were strongly associated with autism risk, motor, and language scores at 18 months. Subsample analyses revealed that the same cerebellar connections strongly correlating with breaks at term age were associated with language dysfunction at 18 months.

CONCLUSIONS

These results have significant implications for the clinical care of preterm infants undergoing painful exposures during routine NICU care, which typically occurs without anesthesia. Repeated pain exposures appear to have an increasingly detrimental effect on brain development during a critical period, and effects continue to be seen even 18 months later.

Does fetal growth restriction induce neuropathology within the developing brainstem?

Fetal growth restriction (FGR) is a complex obstetric issue describing a fetus that does not reach its genetic growth potential. The primary cause of FGR is placental dysfunction resulting in chronic fetal hypoxaemia, which in turn causes altered neurological, cardiovascular and respiratory development, some of which may be pathophysiological, particularly for neonatal life. The brainstem is the critical site of cardiovascular, respiratory and autonomic control, but there is little information describing how chronic hypoxaemia and the resulting FGR may affect brainstem neurodevelopment. This review provides an overview of the brainstem-specific consequences of acute and chronic hypoxia, and what is known in FGR. In addition, we discuss how brainstem structural alterations may impair functional control of the cardiovascular and respiratory systems. Finally, we highlight the clinical and translational findings of the potential roles of the brainstem in maintaining cardiorespiratory adaptation in the transition from fetal to neonatal life under normal conditions and in response to the pathological environment that arises during development in growth-restricted infants. This review emphasises the crucial role that the brainstem plays in mediating cardiovascular and respiratory responses during fetal and neonatal life. We assess whether chronic fetal hypoxaemia might alter structure and function of the brainstem, but this also serves to highlight knowledge gaps regarding FGR and brainstem development.

Corpus callosum-fastigium and tectal lengths in late-onset small fetuses

OBJECTIVE

To investigate measurements on neurosonography of midbrain morphology, including corpus callosum-fastigium length and tectal length, in late-onset small fetuses subclassified as small-for-gestational-age (SGA) or growth-restricted (FGR).

METHODS

This was a case-control study of consecutive singleton pregnancies delivered at term at a single center between January 2019 and July 2021, including those with late-onset smallness (estimated fetal weight (EFW) < 10th centile) and appropriate-for-gestational-age controls matched by age at neurosonography. Small fetuses were further subdivided into SGA (EFW between 3rd and 9th centile and normal fetoplacental Doppler) and FGR (EFW < 3rd centile or EFW < 10th centile with abnormal cerebroplacental ratio and/or uterine artery Doppler). Transvaginal neurosonography was performed at a mean ± SD gestational age of 33 ± 1 weeks in all fetuses to evaluate corpus callosum-fastigium length and tectal length in the midsagittal plane. Intra- and interobserver agreement was evaluated using the intraclass correlation coefficient and Bland-Altman plots.

RESULTS

A total of 70 fetuses with late-onset smallness (29 with SGA and 41 with FGR) and 70 controls were included. Compared with controls, small fetuses showed significantly shorter corpus callosum-fastigium length (median (interquartile range), 44.7 (43.3-46.8) mm vs 43.7 (42.4-45.5) mm, P < 0.001) and tectal length (mean ± SD, 10.5 ± 0.9 vs 9.6 ± 1.0 mm, P < 0.001). These changes were more prominent in FGR fetuses, with a linear trend across groups according to severity of smallness. Corpus callosum-fastigium length and tectal length measurements showed excellent intra- and interobserver reliability.

CONCLUSIONS

Small fetuses exhibited shorter corpus callosum-fastigium length and tectal length compared with controls, and these differences were more pronounced in fetuses with more severe smallness. These findings illustrate the potential value of midbrain measurements assessed on neurosonography as biomarkers for brain development in a high-risk population. However, further studies correlating these parameters with postnatal functional tests and follow-up are needed. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Second trimester fetal MRI of the brain: Through the ground glass

Fetal MRI is an important tool for the prenatal diagnosis of brain malformations and is often requested after second-trimester ultrasonography reveals a possible abnormality. Despite the immature state of the fetal brain at this early stage, early suggestive signs of the presence of brain malformations can be recognized. To differentiate between the normal dynamics of the growing brain and the developing pathological conditions can be challenging and requires extensive knowledge of normal central nervous system developmental stages and their neuroradiological counterparts at those different stages. This article reviews the second-trimester appearances of some commonly encountered brain malformations, focusing on helpful tricks and subtle signs to aid in the diagnosis of such conditions as rhombencephalosynapsis, various causes of vermian rotation, molar tooth spectrum anomalies, diencephalic-mesencephalic junction dysplasia, ganglionic eminence anomalies, and the most common malformations of cortical development.

Fetal Brain Anatomy

"Fetal brain development has been well studied, allowing for an ample knowledge of the normal changes that occur during gestation. Imaging modalities used to evaluate the fetal central nervous system (CNS) include ultrasound and MRI. MRI is the most accurate imaging modality for parenchymal evaluation and depiction of developmental CNS anomalies. The depiction of CNS abnormalities in a fetus can only be accurately made when there is an understanding of its normal development. This article reviews the expected normal fetal brain anatomy and development during gestation. Additional anatomic structures seen on brain imaging sequences are also reviewed."

Quantification of Intracranial Structures Volume in Fetuses Using 3-D Volumetric MRI: Normal Values at 19 to 37 Weeks' Gestation

Objective

The purpose of this study is to establish a reference of intracranial structure volumes in normal fetuses ranging from 19 to 37 weeks' gestation (mean 27 weeks).

Materials and Methods

A retrospective analysis of 188 MRI examinations (1.5 T) of fetuses with a normal brain appearance (19–37 gestational weeks) from January 2018 to December 2021 was included in this study. Three dimensional (3-D) volumetric parameters from slice-to-volume reconstructed (SVR) images, such as total brain volume (TBV), cortical gray matter volume (GMV), subcortical brain tissue volume (SBV), intracranial cavity volume (ICV), lateral ventricles volume (VV), cerebellum volume (CBV), brainstem volume (BM), and extra-cerebrospinal fluid volume (e-CSFV), were quantified by manual segmentation from two experts. The mean, SD, minimum, maximum, median, and 25th and 75th quartiles for intracranial structures volume were calculated per gestational week. A linear regression analysis was used to determine the gestational weekly age-related change adjusted for sex. A t-test was used to compare the mean TBV and ICV values to previously reported values at each gestational week. The formulas to calculate intracranial structures volume derived from our data were created using a regression model. In addition, we compared the predicted mean TBV values derived by our formula with the expected mean TBV predicted by the previously reported Jarvis' formula at each time point. For intracranial volumes, the intraclass correlation coefficient (ICC) was calculated to convey association within and between observers.

Results

The intracranial volume data are shown in graphs and tabular summaries. The male fetuses had significantly larger VV compared with female fetuses (p = 0.01). Measured mean ICV values at 19 weeks are significantly different from those published in the literature (p &lt; 0.05). Means were compared with the expected TBV generated by the previously reported formula, showing statistically differences at 22, 26, 29, and 30 weeks' gestational age (GA) (all p &lt; 0.05). A comparison between our data-derived formula and the previously reported formula for TBV showed very similar values at every GA. The predicted TBV means derived from the previously reported formula were all within the 95% confidence interval (CI) of the predicted means of this study. Intra- and inter-observer agreement was high, with an intraclass correlation coefficient larger than 0.98.

Conclusion

We have shown that the intracranial structural volume of the fetal brain can be reliably quantified using 3-D volumetric MRI with a high degree of reproducibility and reinforces the existing data with more robust data in the earlier second and third stages of pregnancy.

Early second-trimester three-dimensional transvaginal neurosonography of fetal midbrain and hindbrain: normative data and technical aspects

OBJECTIVES

To provide a detailed description of the sonographic appearance and development of various fetal structures of the midbrain and hindbrain (MBHB) during the early second trimester, and to evaluate the impact of the frequency of the transvaginal sonography (TVS) transducer on the early recognition of these structures.

METHODS

This was a retrospective analysis of three-dimensional volumetric datasets of the MBHB from apparently normal fetuses at 14-19 gestational weeks, acquired by TVS in the midsagittal view through the posterior fontanelle. Using a multiplanar approach, we measured the tectal thickness and length, aqueductal thickness, tegmental thickness and width and height of the Blake's pouch (BP) neck. In addition, we assessed the existence of early vermian fissures, the linear shape of the brainstem and the components of the fastigium. The correlation between gestational age according to last menstrual period and sonographic measurements of MBHB structures was evaluated using Pearson's correlation (r). A subanalysis was performed to assess the performance of a 5-9-MHz vs a 6-12-MHz TVS transducer in visualizing the MBHB structures in the early second trimester.

RESULTS

Sixty brain volumes were included in the study, obtained at a mean gestational age of 16.2 weeks (range, 14.1-19.0 weeks), with a transverse cerebellar diameter range of 13.0-19.8 mm. We found a strong correlation between gestational age and all MBHB measurements, with the exception of the tectal, tegmental and aqueductal thicknesses, for which the correlation was moderate. There was good-to-excellent intraobserver and moderate-to-good interobserver correlation for most MBHB measurements. We observed that the BP neck was patent in all fetuses between 14 and 18 weeks with decreasing diameter, and that the aqueductal thickness was significantly smaller at ≥ 18 weeks compared with at < 16 weeks. The early vermian fissures and the linear shape of the brainstem were present in all fetuses from 14 weeks. We found that, in the early second trimester, the horizontal arm of the presumed 'fastigium' evolves from the fourth ventricular choroid plexus and not the posterior vermis, indicating that this is not the fastigium. Standard- and high-resolution TVS transducers performed similarly in the assessment of MBHB anatomy.

CONCLUSION

Detailed early second-trimester assessment of the MBHB is feasible by transvaginal neurosonography and provides reference data which may help in the early detection of brain pathology involving the MBHB. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Three-Dimensional Volumetric Magnetic Resonance Imaging Detects Early Alterations of the Brain Growth in Fetuses With Congenital Heart Disease

BACKGROUND

Several published studies have shown alterations of brain development in third-trimester fetuses with congenital heart disease (CHD). However, little is known about the timing and pattern of altered brain development in fetuses with CHD.

PURPOSE

To investigate the changes in the volume of intracranial structures in fetuses with CHD by three-dimensional (3D) volumetric magnetic resonance imaging (MRI) in the earlier stages of pregnancy (median gestational age [GA], 26 weeks).

STUDY TYPE

Retrospective.

POPULATION

Forty women carrying a fetus with CHD (including 20 fetuses with GA <26 weeks) and 120 pregnant women carrying a healthy fetus (including 50 fetuses with GA <26 weeks).

FIELD STRENGTH/SEQUENCE

Two-dimensional single-shot turbo spin echo sequence at 1.5 -T.

ASSESSMENT

Three-dimensional volumetric parameters from slice-to-volume registered images, including cortical gray matter volume (GMV), subcortical brain tissue volume (SBV), intracranial cavity volume (ICV), lateral ventricles volume (VV), cerebellum, brainstem, and extra-cerebrospinal fluid (e-CSF) were quantified by manual segmentation from one primary and two secondary observers.

STATISTICAL TESTS

Volumes were presented graphically with quadratic curve fitting. Scatterplots were produced mapping volumes against GA in normal and CHD fetuses. For GA <26 weeks, Z scores were calculated and Student's t-tests were conducted to compare volumes between the normal and CHD fetuses.

RESULTS

In fetuses with CHD GMV, SBV, cerebellum, and brainstem were significantly reduced (all P < 0.05) in early stages of pregnancy (GA <26 weeks), with differences becoming progressively greater with increasing GA. Compared with normal fetuses, e-CSF, e-CSF to ICV ratio, and VV were higher in fetuses with CHD (all P < 0.05). However, ICV volume and the GMV to SBV ratio were not significantly reduced in the CHD group (P = 0.94 and P = 0.13, respectively) during the middle gestation (GA <26 weeks).

DATA CONCLUSION

There appear to be alterations of brain development trajectory in CHD fetuses that can be detected by 3D volumetric MRI in the earlier stages of pregnancy.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY: Stage 3.

Fetal Brain Biometric Measurements on 3D Super-Resolution Reconstructed T2-Weighted MRI: An Intra- and Inter-observer Agreement Study

We present the comparison of two-dimensional (2D) fetal brain biometry on magnetic resonance (MR) images using orthogonal 2D T2-weighted sequences (T2WSs) vs. one 3D super-resolution (SR) reconstructed volume and evaluation of the level of confidence and concordance between an experienced pediatric radiologist (obs1) and a junior radiologist (obs2). Twenty-five normal fetal brain MRI scans (18-34 weeks of gestation) including orthogonal 3-mm-thick T2WSs were analyzed retrospectively. One 3D SR volume was reconstructed per subject based on multiple series of T2WSs. The two observers performed 11 2D biometric measurements (specifying their level of confidence) on T2WS and SR volumes. Measurements were compared using the paired Wilcoxon rank sum test between observers for each dataset (T2WS and SR) and between T2WS and SR for each observer. Bland-Altman plots were used to assess the agreement between each pair of measurements. Measurements were made with low confidence in three subjects by obs1 and in 11 subjects by obs2 (mostly concerning the length of the corpus callosum on T2WS). Inter-rater intra-dataset comparisons showed no significant difference (p > 0.05), except for brain axial biparietal diameter (BIP) on T2WS and for brain and skull coronal BIP and coronal transverse cerebellar diameter (DTC) on SR. None of them remained significant after correction for multiple comparisons. Inter-dataset intra-rater comparisons showed statistical differences in brain axial and coronal BIP for both observers, skull coronal BIP for obs1, and axial and coronal DTC for obs2. After correction for multiple comparisons, only axial brain BIP remained significantly different, but differences were small (2.95 ± 1.73 mm). SR allows similar fetal brain biometry as compared to using the conventional T2WS while improving the level of confidence in the measurements and using a single reconstructed volume.