MR Imaging Diagnosis of Diencephalic-Mesencephalic Junction Dysplasia in Fetuses with Developmental Ventriculomegaly

Many Faces of Diencephalic-Mesencephalic Junction Dysplasia Syndrome with GSX2 and PCDH12 Variants

Introduction

Diencephalic-mesencephalic junction dysplasia syndrome is a rare neurogenetic disorder reported to be caused by variants in several genes. Phenotypic presentation is characterized by clinical findings including developmental delay, hypotonia, spasticity, and dyskinetic movements in combination with distinctive imaging features on brain magnetic resonance imaging (MRI).

Methods

Whole exome sequencing was conducted to unveil the molecular etiology of patients presenting with neurological manifestations from two unrelated families.

Results

To the best of our knowledge, here we report the third family affected with diencephalic-mesencephalic junction dysplasia caused by a novel variant in GSX2 and two siblings with a PCDH12 variant exhibiting a less severe phenotype. The siblings with a PCDH12 variant were positioned at the milder end of the phenotypic spectrum. Although both exhibited a clinical phenotype resembling cerebral palsy, one showed partial fusion of the hypothalamus and mesencephalon, whereas MRI was unremarkable in the other. Biallelic GSX2 variants have been implicated in basal ganglia agenesis, and similarly, our patients had basal ganglia hypoplasia along with hypothalamic-mesencephalic fusion.

Conclusion

Identifying variants associated with the syndrome in different genes will contribute to genotype-phenotype correlation.

Loss of symmetric cell division of apical neural progenitors drives DENND5A-related developmental and epileptic encephalopathy

Developmental and epileptic encephalopathies (DEEs) are a heterogenous group of epilepsies in which altered brain development leads to developmental delay and seizures, with the epileptic activity further negatively impacting neurodevelopment. Identifying the underlying cause of DEEs is essential for progress toward precision therapies. Here we describe a group of individuals with biallelic variants in DENND5A and determine that variant type is correlated with disease severity. We demonstrate that DENND5A interacts with MUPP1 and PALS1, components of the Crumbs apical polarity complex, which is required for both neural progenitor cell identity and the ability of these stem cells to divide symmetrically. Induced pluripotent stem cells lacking DENND5A fail to undergo symmetric cell division during neural induction and have an inherent propensity to differentiate into neurons, and transgenic DENND5A mice, with phenotypes like the human syndrome, have an increased number of neurons in the adult subventricular zone. Disruption of symmetric cell division following loss of DENND5A results from misalignment of the mitotic spindle in apical neural progenitors. A subset of DENND5A is localized to centrosomes, which define the spindle poles during mitosis. Cells lacking DENND5A orient away from the proliferative apical domain surrounding the ventricles, biasing daughter cells towards a more fate-committed state and ultimately shortening the period of neurogenesis. This study provides a mechanism behind DENND5A-related DEE that may be generalizable to other developmental conditions and provides variant-specific clinical information for physicians and families.

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.

L1CAM variants cause two distinct imaging phenotypes on fetal MRI

Data on fetal MRI in L1 syndrome are scarce with relevant implications for parental counseling and surgical planning. We identified two fetal MR imaging patterns in 10 fetuses harboring L1CAM mutations: the first, observed in 9 fetuses was characterized by callosal anomalies, diencephalosynapsis, and a distinct brainstem malformation with diencephalic–mesencephalic junction dysplasia and brainstem kinking. Cerebellar vermis hypoplasia, aqueductal stenosis, obstructive hydrocephalus, and pontine hypoplasia were variably associated. The second pattern observed in one fetus was characterized by callosal dysgenesis, reduced white matter, and pontine hypoplasia. The identification of these features should alert clinicians to offer a prenatal L1CAM testing.

Prevalence of the interthalamic adhesion in the human brain: a review of literature

The interthalamic adhesion (IA) is a midline structure connecting the two thalami. Though it has been studied for centuries its exact function remains elusive. Early studies had noted its peculiar absence even among some healthy individuals. Population studies have investigated the differences in prevalence of IA in pathologic conditions and healthy controls. However, there is a general lack of consensus on IA prevalence in the healthy population. Understanding the true prevalence is critical in providing context for future studies, as well as uncovering further clues regarding IA's function. We systematically reviewed the existing literature to evaluate the prevalence of IA. The average prevalence among reviewed studies was higher than previously reported, at 87.3%. Studies utilizing magnetic resonance imaging rather than cadaveric specimens reported higher rates of IA prevalence. A higher prevalence among females was noted throughout the literature that persisted regardless of acquisition modality utilized.

Fetal MRI assessment of posterior fossa anomalies: A review

Prenatal ultrasound (US) is the first prenatal imaging tool for screening and evaluation of posterior fossa malformations since it is noninvasive, widely available, and safe for both mother and child. Fetal MRI is a widely used secondary technique to confirm, correct, or complement questionable US findings and plays an essential role in evaluating fetuses with suspected US findings and /or positive family history. The main sequences of fetal MRI consist of T2-weighted (T2w) ultrafast, single-shot sequences. Axial, coronal, and sagittal images are typically acquired allowing for a detailed evaluation of the posterior fossa contents. Also, various complimentary sequences, such as T1w, T2*w gradient sequences, or advanced techniques, including diffusion-weighted imaging, diffusion tensor imaging, and magnetic resonance spectroscopy, may provide additional information based on the studied malformation. Inclusion of these techniques should be done with careful risk-benefit analysis. The use of fetal MRI also aims to evaluate for associated anomalies. In addition, prenatal diagnosis of posterior fossa malformations is still a challenge but advances in knowledge in human developmental anatomy, genetic, and imaging recognition patterns have enabled us to shed some light on prognostic information that will help with the counseling of families. Finally, high-resolution late third trimester fetal MRI offers a safe alternative to early postnatal MR imaging, basically taking advantage of the uterine environment as a kind of "maternal incubator." Our goal is to discuss the spectrum of prenatal posterior fossa pathologies that can be studied by fetal MRI and their key neuroimaging features.

Prenatal diagnosis of diencephalic-mesencephalic junction dysplasia: Fetal magnetic resonance imaging phenotypes, genetic diagnoses, and outcomes

OBJECTIVE

Report a single-center 12-year experience in the fetal diagnosis of diencephalic-mesencephalic junction dysplasia (DMJD) to expand the phenotype with Magnetic resonance imaging (MRI)-based classification, evaluate genetic etiologies, and ascertain outcomes.

METHODS

Retrospective medical record and imaging review of all fetal MRI exams with DMJD were performed at our institution.

RESULTS

Thirty-three pregnancies with fetal MRI findings of DMJD at 24 (18-37) weeks gestational age were studied; 70% were referred for fetal hydrocephalus. Three fetal MRI patterns were recognized. Type A (butterfly/hypothalamus-midbrain union) was seen in two cases (6%), Type B (partial thalamus-midbrain union) in 22 fetuses (70%), and Type C (complete/near complete midbrain-thalamic continuity) in nine fetuses (24%). L1CAM mutations were identified in four cases, and biallelic VRK1 variants in another. Among 14 live-born cases, 11 survived infancy, and 10 underwent postnatal brain MRI which confirmed the fetal MRI diagnosis in all but one case. Development was delayed in all surviving infants, most with additional neurological sequelae.

CONCLUSIONS

DMJD may be identified by prenatal MRI as early as 18 weeks gestation. We propose three distinct phenotypic forms of DMJD, Types A-C. Next-generation sequencing provides an underlying molecular diagnosis in some patients, but further studies on associated genetic diagnoses and clinical outcomes are indicated.

Magnetic resonance imaging of the brainstem in children, part 1: imaging techniques, embryology, anatomy and review of congenital conditions

Part 1 of this series of two articles describes conventional and advanced MRI techniques that are useful for evaluating brainstem pathologies. In addition, it provides a review of the embryology, normal progression of myelination, and clinically and radiologically salient imaging anatomy of the normal brainstem. Finally, it discusses congenital diseases of the brainstem with a focus on distinctive imaging features that allow for differentiating pathologies. Part 2 of this series of two articles includes discussion of neoplasms; infections; and vascular, demyelinating, toxic and metabolic, and miscellaneous disease processes affecting the brainstem. The ultimate goal of this pair of articles is to empower the radiologist to add clinical value in the care of pediatric patients with brainstem pathologies.

Fetal Neuroimaging Update

OBJECTIVES

To review the current imaging techniques available for the evaluation of the fetal brain.

FINDINGS

Ultrasound remains the initial screening modality with routine scanning typically performed at 18-20 weeks gestation. When a central nervous system (CNS) abnormality is noted by ultrasound, MRI is increasingly being used to further clarify findings. Fetal MRI has the unique ability to provide high detailed anatomical information of the entire human fetus with high contrast resolution. This technique has grown due to the development of rapid single shot image acquisition sequences, improvement of motion correction strategies and optimizing shimming techniques.

CONCLUSIONS

The assessment of fetal CNS anomalies continues to improve. Advanced MRI techniques have allowed for further delineation of CNS anomalies and have become a cornerstone in the assessment of fetal brain well-being. Those interpreting fetal studies need to be familiar with the strengths and limitations of each exam and be sensitive to the impact discussing findings can have regarding perinatal care and delivery planning. Collaboration with neurologists, neurosurgeons, geneticists, counselors, and maternal fetal specialists are key in providing the best care to the families we treat.

Prenatal diagnosis of brainstem anomalies

Prenatal diagnosis of brainstem anomalies is important due to the usually associated neurodevelopmental impairment and genetic implications. The extreme developmental changes that the brainstem and cerebellum undergo during fetal life pose a challenge for the characterization and definition of the different malformations. The present review aims to demonstrate the normal development of the fetal brainstem and to present the main features required for diagnosis of its anomalies according to available data in the medical literature.

Loss of Protocadherin-12 Leads to Diencephalic-Mesencephalic Junction Dysplasia Syndrome

OBJECTIVE

To identify causes of the autosomal-recessive malformation, diencephalic-mesencephalic junction dysplasia (DMJD) syndrome.

METHODS

Eight families with DMJD were studied by whole-exome or targeted sequencing, with detailed clinical and radiological characterization. Patient-derived induced pluripotent stem cells were derived into neural precursor and endothelial cells to study gene expression.

RESULTS

All patients showed biallelic mutations in the nonclustered protocadherin-12 (PCDH12) gene. The characteristic clinical presentation included progressive microcephaly, craniofacial dysmorphism, psychomotor disability, epilepsy, and axial hypotonia with variable appendicular spasticity. Brain imaging showed brainstem malformations and with frequent thinned corpus callosum with punctate brain calcifications, reflecting expression of PCDH12 in neural and endothelial cells. These cells showed lack of PCDH12 expression and impaired neurite outgrowth.

INTERPRETATION

DMJD patients have biallelic mutations in PCDH12 and lack of protein expression. These patients present with characteristic microcephaly and abnormalities of white matter tracts. Such pathogenic variants predict a poor outcome as a result of brainstem malformation and evidence of white matter tract defects, and should be added to the phenotypic spectrum associated with PCDH12-related conditions. Ann Neurol 2018;84:646-655.