Magnetic resonance imaging and the detection of fetal brain anomalies, injury, and physiologic adaptations

Evolving fetal phenotypes and clinical impact of progressive prenatal exome sequencing pathways: cohort study

OBJECTIVES

To determine (1) the diagnostic yield and turnaround time (TAT) of two consecutive prenatal exome sequencing (ES) pathways, (2) the evolution of the fetal phenotype and (3) the clinical impact of detecting causative pathogenic variants and incidental findings.

METHODS

This was a retrospective cohort analysis of prospectively collected fetal cases that underwent trio ES in the presence of a structural anomaly and normal chromosomal microarray testing in the West Midlands Regional Genetics Laboratory, Birmingham, UK. The study included two phases: (1) between July 2018 and October 2020, the clinical pathway from the Prenatal Assessment of Genomes and Exomes (PAGE) study was adopted and involved prenatal trio ES based on a panel of 1542 development disorder genes and case selection by a multidisciplinary team; (2) between October 2020 and July 2021, prenatal trio ES investigation was based on the National Health Service (NHS) England R21 pathway, with definitive inclusion criteria and a panel of 1205 prenatally relevant genes. Deep phenotyping was performed throughout pregnancy and postnatally.

RESULTS

A total of 54 cases were included. The diagnostic yield before vs after R21 pathway implementation was 28.0% (7/25) and 55.2% (16/29), respectively (P = 0.04). The respective values for mean TAT were 54.0 days (range, 14-213 days) and 14.2 days (range, 3-29 days). In cases in which a causative pathogenic variant was identified and in which the pregnancy reached the third trimester, additional anomalies were detected between the second and third trimesters in 73.3% (11/15) of cases, predominantly secondary to progressive hydropic features (3/11 (27.3%)), arthrogryposis (3/11 (27.3%)) or brain anomaly (2/11 (18.2%)). In three cases, a variant of uncertain significance was reclassified to likely pathogenic based on postnatal information. Detection of a causative pathogenic variant had a significant clinical impact in 78.3% (18/23) of cases, most frequently affecting decision-making regarding the course of the pregnancy and neonatal management (7/18 (38.9%)).

CONCLUSIONS

Prenatal ES using the NHS England R21 pathway showed great promise when applied to this cohort, allowing a genetic diagnosis to be made in over half of preselected cases with a fetal structural anomaly on ultrasound. Monitoring and real-time updating of fetal phenotype and reclassification of variants based on postnatal findings is vital to increase the clinical impact that is already evident from this emerging genomic technology. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

A correlation between Magnetic Resonance Spectroscopy (1-H MRS) and the neurodevelopment of two-year-olds born preterm in an EPIRMEX cohort study

BACKGROUND

Preterm infants are at risk of neurodevelopmental impairments. At present, proton magnetic resonance spectroscopy (1H-MRS) is currently used to evaluate brain metabolites in asphyxiated term infants. The purpose of this study was to identify in the preterm EPIRMEX cohort any correlations between (1H-MRS) metabolites ratio at term equivalent age (TEA) and neurodevelopmental outcomes at 2 years.

METHODS

Our study included EPIRMEX eligible patients who were very preterm infants (gestational age at birth ≤32 weeks) and who underwent a brain MRI at TEA and ¹H-MRS using a monovoxel technique. The volumes of interest (VOI) were periventricular white matter posterior area and basal ganglia. The ratio of N Acetyl Aspartate (NAA) to Cho (Choline), NAA to Cr (creatine), Cho to Cr, and Lac (Lactate) to Cr were measured. Neurodevelopment was assessed at 24 months TEA with ASQ (Ages and Stages Questionnaire).

RESULTS

A total of 69 very preterm infants had a 1H-MRS at TEA. In white matter there was a significant correlation between a reduction in the NAA/Cho ratio and a total ASQ and/or abnormal communication score, and an increase in the Lac/Cr ratio and an abnormality of fine motor skills. In the gray nuclei there was a trend correlation between the reduction in the NAA/Cho ratio and sociability disorders; and the increase in the Lac/Cr ratio and an anomaly in problem-solving.

CONCLUSIONS

Using NAA as a biomarker, the vulnerability of immature oligodendrocytes in preterm children at TEA was correlated to neurodevelopment at 2 years. Similarly, the presence of lactate at TEA was associated with abnormal neurodevelopment at 2 years in the preterm brain.

Fetale und neonatale Alloimmunthrombozytopenie, Teil 2

Die fetale und neonatale Alloimmunthrombozytopenie (FNAIT) wird durch mütterliche Antikörper hervorgerufen, die gegen ein vom Vater ererbtes Blutgruppenmerkmal an fetalen Thrombozyten gerichtet sind. Während Teil 1 des Beitrags Ausgabe die Ätiologie, die Pathogenese und die Diagnostik der FNAIT thematisiert hatte, widmet sich dieser 2. Teil der Risikostratifizierung und Behandlung 1.

Findings and differential diagnosis of fetal intracranial haemorrhage and fetal ischaemic brain injury: what is the role of fetal MRI?

Ventriculomegaly (VM) is a non-specific finding on fetal imaging. Identification of the specific aetiology is important, as it affects prognosis and may even change the course of current or future pregnancies. In this review, we will focus on the application of fetal MRI to demonstrate intracranial haemorrhage and ischaemic brain injury as opposed to other causes of VM. MRI is able to identify the specific aetiology of VM with much more sensitivity and specificity than ultrasound and should be considered whenever VM is identified on obstetric ultrasound. Advances in both fetal and neonatal MRI have the potential to shed further light on mechanisms of brain injury and the impact of chronic hypoxia; such information may guide future interventions.

Serial fetal MRI for the diagnosis of Aicardi syndrome

Aicardi syndrome (AS) is defined by the triad of corpus callosum agenesis, chorioretinal "lacunae" and infantile spasms. Additional neuroimaging findings including migrational abnormalities are common. We report on serial neuroimaging findings of a female fetus with ventriculomegaly, corpus callosum agenesis and focal migrational abnormalities, suggestive of AS. Postnatal neuroimaging follow-up as well as ophthalmological evaluation and occurrence of infantile spasms confirmed the prenatally suspected diagnosis of AS. This case points out the key role of serial fetal magnetic resonance imaging (MRI) in detecting the full spectrum of pathologies associated with fetal ventriculomegaly. The associated neuroimaging findings may go undetected on prenatal ultrasound, but are important in terms of diagnosis and counseling of the parents. Additionally, this case emphasizes the importance of serial fetal MRI studies to more accurately delineate the progression of findings during brain development.

The brain in the belly: what and how of fetal neuroimaging?

This work reviews magnetic resonance imaging in the developing human brain. It focuses on fetal brain imaged in vivo and in utero with complementary sections on abnormalities seen in clinical settings, and on potential of diffusion tensor imaging and of proton magnetic resonance spectroscopy. The main purposes are to illustrate the normal fetal developing brain and its abnormalities commonly encountered in utero, and to emphasize the potential role of adjunct techniques such as diffusion imaging and spectroscopy that may help elucidate fetal brain maturation and its abnormalities.

Magnetic resonance imaging of fetal developmental anomalies

Fetal developmental anomalies consist of central nervous system malformations, brain injury, and tumors. Overlap is often seen especially between malformation and injury because malformation may be genetically determined or related to external causative agent, whereas brain injury may be, on one hand, caused by malformation as with intracranial vascular malformation and, on another, can cause brain malformation when cerebral insult occurs during organogenesis and histogenesis. The goal of this review was not to describe by magnetic resonance imaging (MRI) all fetal developmental anomalies encountered in utero; it is most likely to focus on fetal brain anomalies that either are most commonly seen in fetal tertiary care facility or are extremely challenging for MRI. Consequently, the potential of advanced MR techniques such as proton MR spectroscopy and diffusion tensor imaging is also described especially when a challenge is highlighted. This review is therefore organized in subchapters as follows. The first section gives the place of MRI in prenatal development and cites the standard protocol and the advanced techniques. The rules of fetal brain MRI, the challenge and pitfalls, and the selection of MRI cases follow as 3 subchapters. Also, abnormalities are described as 3 separate subchapters entitled ventriculomegalies (hydrocephalus), malformations, and brain injury.

3D and 4D sonography and magnetic resonance in the assessment of normal and abnormal CNS development: alternative or complementary

Advanced transvaginal neurosonography has revealed normal and abnormal intracranial morphology. Transvaginal three-dimensional (3D) sonography demonstrates bony structure, multiplanar analysis of inside detailed morphology, tomographic ultrasound imaging in any cutting sections, 3D sonoangiography and volume calculation of ventricles and/or intracranial lesions. Longitudinal assessment of normal and abnormal central nervous system (CNS) development is done by serial scanning. However, the transvaginal high-frequency approach has several limitations due to lack of penetration and cranial bone ossification with advanced gestational age. Magnetic resonance neuroimaging enabled observation of the whole intracranial cavity, brainstem and cortical gyral/sulcal development. On the other hand, neuro-sonography has advantages in detecting intracranial calcification, vascular abnormalities, intratumoral vascularity and bone dysplasia. Moreover, 3D ultrasound demonstrates extra CNS abnormalities, strongly associated with CNS abnormalities. Any less-invasive modalities can be used for a CNS anomaly screening scan and ultrasound is no doubt the first choice. Once CNS abnormality is suspected, it is suggested to use the different technologies according to what is looked for in each abnormal CNS case. Of course, MR and 3D ultrasound imaging should be complementary as well as alternative.

Fetal magnetic resonance imaging of acquired and developmental brain anomalies

During the last decade, increasing interest in magnetic resonance imaging has emerged for the evaluation of fetal abnormalities detected on ultrasound. The advent of single-shot rapid acquisition sequences has greatly facilitated our ability to obtain detailed imaging information of the fetal brain. To date, fetal magnetic resonance imaging has shown to have an important role in the investigation of cerebral abnormalities suspected by sonography, and in the detection of subtle brain anomalies associated with high-risk pregnancies. Magnetic resonance imaging has proved to be a useful adjunct to sonography during the prenatal period of development, especially for the detection of acquired disorders.

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.

MR imaging of brain maturation

Magnetic resonance imaging (MRI) is the imaging tool of choice to evaluate brain maturation and especially brain myelination. Magnetic resonance imaging also provides functional insight through diffusion images and proton spectroscopy. In this review the MRI techniques are analyzed for both pre- and postnatal periods. The origin of MR signal changes is also detailed in order to understand normal myelination evolution and the consequences on brain maturation of the different pathologies encountered prior and after birth. Because MRI is "blind" in terms of signal on conventional sequences after 2 years of age, a particular attention is given to diffusion images and proton spectroscopy of the developing brain.

Fetal Magnetic Resonance Imaging as a Complement to Fetal Ultrasonography

Ultrasonography is the screening method of choice for the evaluation of the fetus. It is safe, inexpensive, and easily performed. However, it is operator dependent, and evaluation may be limited because of fetal position, maternal obesity, overlying bone, and/or oligohydramnios. Magnetic resonance imaging is an alternative modality that uses no ionizing radiation, has excellent tissue contrast and a large field of view, is not limited by obesity or overlying bone, and can image the fetus in multiple planes, no matter the fetal lie. Faster scanning techniques allow studies to be performed without sedation in the second and third trimester with minimal motion artifact.

Fetal MR Imaging

Ultrasonography is the primary prenatal screening modality used in the evaluation of the fetus and the maternal pelvis. However, fetal MR imaging plays a complementary role to prenatal ultrasound in the evaluation of the fetus with suspected abnormalities. MR imaging's role includes confirming or excluding possible lesions, defining their full extent, aiding in their characterization, and demonstrating other associated abnormalities. As newer techniques such as diffusion imaging, MR spectroscopy, and functional studies are used more widely, it is hoped that additional information will be made available by this modality to physicians evaluating and taking care of fetuses.