Fetal magnetic resonance imaging: supratentorial brain malformations

[Congenital brain malformations]

CLINICAL ISSUE

Malformations of the central nervous system belong to the most common developmental disorders in humans. The clinical presentation of brain malformations is nonspecific including developmental delay, hypotonia, and/or epilepsy. The great heterogeneity concerning etiology, mechanisms of development and morphology is challenging for diagnosis and classification of brain malformations. Thereby recognizing specific malformations is essential for optimal patient management and prognostic evaluation. The aim of this article is to give an overview of several clinically relevant brain malformations occurring from different disrupted developmental processes in brain formation.

STANDARD RADIOLOGICAL METHODS

Several brain malformations are already diagnosed during routine ultrasound in pregnancy. However pre- and postnatal magnetic resonance imaging remains the gold standard in detecting the partially subtle changes and to classify the malformations.

METHODICAL INNOVATIONS

Advances in pre- and postnatal neuroimaging techniques and increasing investigation of genetic mechanisms underlying brain formation and its abnormalities have led to a better understanding of embryologic development and pathogeneses of brain malformations.

CONCLUSION

Besides patient's history and clinical phenotype, neuroimaging plays a key role in diagnosis. Not always a specific diagnosis can be made, but neuroimaging patterns often enable a focused genetic testing and therefore are revolutionary for etiologic and prognostic assignment. Basic knowledge of brain development facilitates understanding and classifying of structural brain abnormalities.

MR insights into fetal brain development: what is normal and what is not

Fetal brain development is a complex, rapid, and multi-dimensional process that can be documented with MRI. In the second and third trimesters, there are predictable developmental changes that must be recognized and differentiated from disease. This review delves into the key biological processes that drive fetal brain development, highlights normal developmental anatomy, and provides a framework to identify pathology. We will summarize the development of the cerebral hemispheres, sulci and gyri, extra-axial and ventricular cerebrospinal fluid, and corpus callosum and illustrate the most common abnormal findings in the clinical setting.

Fetal MRI of the supratentorial brain abnormalities: what we should know about ventriculomegaly?

Fetal MRI is performed to evaluate the brain in cases where an abnormality is detected by ultrasonography (US). Fetal MRI has higher contrast resolution than US. Because the fetal brain is dynamic structure, it is important to know the normal appearance of the brain at different gestational age to be better able to identify abnormalities using MRI. Fast imaging sequences to minimize artifact from fetal motion are required. The main sequences used are ultrafast T2 weighted imaging. Similar to pediatric neuroimaging, images are acquired in the axial, sagittal, and coronal planes. T1 weighted image and Gradient echo-planar T2 weighted images are performed to detect hemorrhage. Ventriculomegaly is the most common central nervous system abnormality identified on US. The causes of ventriculomegaly are very heterogeneous and include developmental, destructive, and obstructive processes, or a combination thereof. MRI improves diagnostic accuracy and can be used to evaluate the etiology of the ventriculomegaly. Moreover, MRI can play an important role in detecting additional findings, which may help to focus on patient counseling and management. This review summarizes and illustrates common pattern of ventriculomegaly due to mainly supratentorial abnormalities.

Fetal MRI Neuroradiology: Indications

Fetal MRI is a safe, noninvasive examination of the fetus and placenta, a complement to ultrasonography. MRI provides detailed CNS evaluation, including depicting parenchymal architecture and posterior fossa morphology, and is key in prenatal assessment of spinal dysraphism, neck masses, and ventriculomegaly. Fetal MRI is typically performed after 22 weeks gestation, and ultrafast T1 and T2-weighted MRI sequences are the core of the exam, with advanced sequences such as diffusion weighted imaging used for specific questions. The fetal brain grows and develops rapidly, and familiarity with gestational age specific norms is essential to MRI interpretation.

Prenatal diagnosis of Miller-Dieker syndrome/PAFAH1B1-related lissencephaly: Ultrasonography and genetically investigative results

OBJECTIVE

To present the experience on prenatal diagnosis of Miller-Dieker syndrome (MDS)/PAFAH1B1-related lissencephaly to further determine fetal phenotypes of this syndrome.

STUDY DESIGN

This was a retrospective study of ten pregnancies with fetal MDS/PAFAH1B1-related lissencephaly identified by chromosomal microarray (CMA)/exome sequencing (ES). Clinical and laboratory data were collected and reviewed for these cases, including maternal demographics, prenatal sonographic findings, CMA or ES results and pregnancy outcomes.

RESULTS

Two cases were diagnosed in the first trimester because of an increased nuchal translucency. The remaining eight cases were identified at late gestation, including four in the second trimester because of fetal cardiac anomalies or ventriculomegaly, and four in the third trimester because of ventriculomegaly. CMA revealed 17p13.3 deletions in nine cases, and ES detected a de novo PAFAH1B1 missense mutation in one case.

CONCLUSION

The prenatal presentation of MDS/PAFAH1B1-related lissencephaly depended on the gestational age when the diagnosis was made. Mild ventriculomegaly was the most common prenatal sonographic sign identified in cases of MDS/PAFAH1B1-related lissencephaly. It is important that fetal MRI and invasive testing with CMA should be considered in fetuses with apparently 'isolated' mild ventriculomegaly.

Antenatal counselling for prospective parents whose fetus has a neurological anomaly: part 2, risks of adverse outcome in common anomalies

After diagnosis of a fetal neurological anomaly, prospective parents want to know the best and worst-case scenarios and an estimation of the risk to their infant of having an atypical developmental outcome. The literature on developmental outcomes for fetal neurological anomalies is poor: studies are characterized by retrospective design, small sample size, often no standardized assessment of development, and differing definitions of anomalies. This review provides an aide-memoir on the risks of adverse neurodevelopmental outcome for ventriculomegaly, cortical anomalies, microcephaly, macrocephaly, agenesis of the corpus callosum, posterior fossa anomalies, and myelomeningocele, to assist healthcare professionals in counselling. The data in this review should be used alongside recommendations on counselling and service design described in part 1 to provide antenatal counselling.

Fetal Neuroimaging Updates

MR imaging is used in conjunction with ultrasound screening for fetal brain abnormalities because it offers better contrast, higher resolution, and has multiplanar capabilities that increase the accuracy and confidence of diagnosis. Fetal motion still severely limits the MR imaging sequences that can be acquired. We outline the current acquisition strategies for fetal brain MR imaging and discuss the near term advances that will improve its reliability. Prospective and retrospective motion correction aim to make the complement of MR neuroimaging modalities available for fetal diagnosis, improve the performance of existing modalities, and open new horizons to understanding in utero brain development.

Lissencephaly: Update on diagnostics and clinical management

Lissencephaly represents a spectrum of rare malformations of cortical development including agyria, pachygyria and subcortical band heterotopia. The progress in molecular genetics has led to identification of 31 lissencephaly-associated genes with the overall diagnostic yield over 80%. In this review, we focus on clinical and molecular diagnosis of lissencephaly and summarize the current knowledge on histopathological changes and their correlation with the MRI imaging. Additionally we provide the overview of clinical follow-up recommendations and available data on epilepsy management in patients with lissencephaly.