Refining the Neuroimaging Definition of the Dandy-Walker Phenotype

Not Dandy Walker variant: a review of prominent retrocerebellar CSF space in children

The prominent retrocerebellar cerebrospinal fluid (CSF) space can be frequently encountered on paediatric neuroimaging studies. In cases involving abnormal vermian development where imaging does not align with the established criteria of Dandy-Walker malformation (DWM), the term "Dandy-Walker variant or continuum" has been historically employed to describe the aberrant posterior fossa development. Instead, the emphasis is on a more elaborate description of the findings in the posterior fossa. Moreover, combining the findings in the supratentorial brain can occasionally predict certain neurogenetic disorders that mimic Dandy-Walker phenotype. The present review demonstrates and differentiates the imaging features of various entities that result in an enlarged retrocerebellar CSF space, such as inferior vermian hypoplasia (IVH) and several neurogenetic conditions.

[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.

Fetal and neonatal outcomes of posterior fossa anomalies: a retrospective cohort study

The primary aim of this study was to estimate the incidence of posterior fossa anomalies (PFA) and assess the associated outcomes in King Abdulaziz Medical City (KAMC), Riyadh. All fetuses diagnosed by prenatal ultrasound with PFA from 2017 to 2021 in KAMC were analyzed retrospectively. PFA included Dandy-Walker malformation (DWM), mega cisterna magna (MCM), Blake's pouch cyst (BPC), and isolated vermian hypoplasia (VH). The 65 cases of PFA were 41.5% DWM, 46.2% MCM, 10.8% VH, and 1.5% BPC. The annual incidence rates were 2.48, 2.64, 4.41, 8.75, and 1.71 per 1000 anatomy scans for 2017, 2018, 2019, 2020, and 2021, respectively. Infants with DWM appeared to have a higher proportion of associated central nervous system (CNS) abnormalities (70.4% vs. 39.5%; p-value = 0.014) and seizures than others (45% vs. 17.9%; p-value = 0.041). Ten patients with abnormal genetic testing showed a single gene mutation causing CNS abnormalities, including a pathogenic variant in MPL, C5orf42, ISPD, PDHA1, PNPLA8, JAM3, COL18A1, and a variant of uncertain significance in the PNPLA8 gene. Our result showed that the most common PFA is DWM and MCM. The autosomal recessive pathogenic mutation is the major cause of genetic disease in Saudi patients diagnosed with PFA.

Undifferentiated psychosis or schizophrenia associated with vermis-predominant cerebellar hypoplasia

Schizophrenia (SCZ) is a well-studied neuropsychiatric condition that has been shown to have a high degree of genetic heritability. Still, little data on the specific genetic risk variants associated with the disease exists. Classification of the SCZ phenotype into SCZ-related endophenotypes is a promising methodology to parse out and elucidate the specific genetic risk variants for each. Here, we present a series of 17 previously reported individuals and a new proband with similar SCZ-related neuropsychiatric characteristics and shared brain imaging findings. Unsurprisingly, these individuals shared classic psychiatric features of SCZ. Interestingly, we also identified shared neuropsychiatric features in this series of individuals that had not been highlighted previously. A consistently decreased IQ, memory impairment, sleep and speech disturbances, and attention deficits were commonly reported findings. The brain imaging findings among these individuals also consistently showed posterior vermis predominant cerebellar hypoplasia (CBLH-V). Most individuals' diagnoses were initially described as Dandy-Walker malformation; however, our independent review of imaging suggests a more consistent pattern of posterior vermis predominant cerebellar hypoplasia rather than true Dandy-Walker malformation. While the specific genetic risk variants for this endophenotype are yet to be described, the aim of this paper is to present the shared neuropsychiatric features and consistent, symmetrical brain image findings which suggest that this subset of individuals comprises an endophenotype of SCZ with a high genetic solve rate.

Splicing variant of WDR37 in a case of Neurooculocardiogenitourinary syndrome

BACKGROUND

Neurooculocardiogenitourinary syndrome (NOCGUS), a multisystemic syndrome characterized by motor disorder, intellectual disability, seizures, abnormal brain structure, ocular diseases, and cardiac diseases, has been reported with missense variant of WD repeat-containing protein 37 (WDR37) in humans. This report aimed to identify the cause of NOCGUS in an affected patient.

CASE PRESENTATION

We identified a de novo intronic 4-bp deletion of WDR37, c.727-27_727-24del, which were predicted to cause abnormal splicing by SpliceAI, in the patient with NOCGUS. Reverse transcription polymerase chain reaction (RT-PCR) revealed intron retention of 63 base pairs before exon 10 in messenger RNA, which was predicted to insert 21 additional aberrant amino acids (p.S242_I243insLCQKKLKISRKCLFWPSLWQQ). The patient had novel phenotypes, anal atresia, and polycystic kidney, in addition to intellectual disability, seizures, cerebellar vermian anomaly, and coloboma, which are typical in NOCGUS. We did not observe motor impairments or cardiovascular anomalies.

CONCLUSION

This is the first reported case of NOCGUS with the splicing variant of WDR37, which manifests with distinctive but variable features. Our findings may expand a possible phenotypic expression of NOCGUS.

Dandy-Walker Phenotype with Brainstem Involvement: 2 Distinct Subgroups with Different Prognosis

BACKGROUND AND PURPOSE

Although cardinal imaging features for the diagnostic criteria of the Dandy-Walker phenotype have been recently defined, there is a large range of unreported malformations among these patients. The brainstem, in particular, deserves careful attention because malformations in this region have potentially important implications for clinical outcomes. In this article, we offer detailed information on the association of brainstem dysgenesis in a large, multicentric cohort of patients with the Dandy-Walker phenotype, defining different subtypes of involvement and their potential clinical impact.

MATERIALS AND METHODS

In this established multicenter cohort of 329 patients with the Dandy-Walker phenotype, we include and retrospectively review the MR imaging studies and clinical records of 73 subjects with additional brainstem malformations. Detailed evaluation of the different patterns of brainstem involvement and their potential clinical implications, along with comparisons between posterior fossa measurements for the diagnosis of the Dandy-Walker phenotype, was performed among the different subgroups of patients with brainstem involvement.

RESULTS

There were 2 major forms of brainstem involvement in patients with Dandy-Walker phenotype including the following: 1) the mild form with anteroposterior disproportions of the brainstem structures "only" (57/73; 78%), most frequently with pontine hypoplasia (44/57; 77%), and 2) the severe form with patients with tegmental dysplasia with folding, bumps, and/or clefts (16/73; 22%). Patients with severe forms of brainstem malformation had significantly increased rates of massive ventriculomegaly, additional malformations involving the corpus callosum and gray matter, and interhemispheric cysts. Clinically, patients with the severe form had significantly increased rates of bulbar dysfunction, seizures, and mortality.

CONCLUSIONS

Additional brainstem malformations in patients with the Dandy-Walker phenotype can be divided into 2 major subgroups: mild and severe. The severe form, though less prevalent, has characteristic imaging features, including tegmental folding, bumps, and clefts, and is directly associated with a more severe clinical presentation and increased mortality.

Neuroimaging Findings in Axenfeld-Rieger Syndrome: A Case Series

Axenfeld-Rieger syndrome is an autosomal dominant condition associated with multisystemic features including developmental anomalies of the anterior segment of the eye. Single nucleotide and copy number variants in the paired-like homeodomain transcription factor 2 (PITX2) and forkhead box C1 (FOXC1) genes are associated with Axenfeld-Rieger syndrome as well as other CNS malformations. We determined the association between Axenfeld-Rieger syndrome and specific brain MR imaging neuroradiologic anomalies in cases with or without a genetic diagnosis. This case series included 8 individuals with pathogenic variants in FOXC1; 2, in PITX2; and 2 without a genetic diagnosis. The most common observation was vertebrobasilar artery dolichoectasia, with 46% prevalence. Other prevalent abnormalities included WM hyperintensities, cerebellar hypoplasia, and ventriculomegaly. Vertebrobasilar artery dolichoectasia and absent/hypoplastic olfactory bulbs were reported in >50% of individuals with FOXC1 variants compared with 0% of PITX2 variants. Notwithstanding the small sample size, neuroimaging abnormalities were more prevalent in individuals with FOXC1 variants compared those with PITX2 variants.

A founder PPIL1 variant underlies a recognizable form of microlissencephaly with pontocerebellar hypoplasia

Biallelic variants in PPIL1 have been recently found to cause a very rare type of pontocerebellar hypoplasia and congenital microcephaly in which simplified gyral pattern was not observed in all of the patients. Here, we describe a series of nine patients from eight unrelated Egyptian families in whom whole exome sequencing detected a previously reported homozygous missense variant (c.295G>A, p.Ala99Thr) in PPIL1. Haplotype analysis confirmed that this variant has a founder effect in our population. All our patients displayed early onset drug-resistant epilepsy, profound developmental delay, and visual impairment. Remarkably, they presented with recognizable imaging findings showing profound microcephaly, hypoplastic frontal lobe and posteriorly predominant pachygyria, agenesis of corpus callosum with colpocephaly, and pontocerebellar hypoplasia. In addition, Dandy-Walker malformation was evident in three patients. Interestingly, four of our patients exhibited hematopoietic disorder (44% of cases). We compared the phenotype of our patients with other previously reported PPIL1 patients. Our results reinforce the hypothesis that the alterative splicing of PPIL1 causes a heterogeneous phenotype. Further, we affirm that hematopoietic disorder is a common feature of the condition and underscore the role of major spliceosomes in brain development.

Congenital melanocytic naevus syndrome and Dandy-Walker malformation - a mistaken association: case report and literature review

Congenital melanocytic naevus (CMN) syndrome, previously termed neurocutaneous melanosis, is a rare disease caused by postzygotic mosaic mutations occurring during embryogenesis in precursors of melanocytes. The severity of neurological manifestations in CMN patients is related to central nervous system abnormalities found at magnetic resonance imaging. The association between CMN and Dandy-Walker malformation (DWM) has been described in the literature, but recent advances in imaging and genetics lead to diagnostic criteria revision. In this paper, we aim to re-evaluate the proposed association by reviewing the available literature and present a patient with CMN and a large posterior fossa cyst.

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 Neurology: From Prenatal Counseling to Postnatal Follow-Up

Brain abnormalities detected in fetal life are being increasingly recognized. Child neurologists are often involved in fetal consultations, and specific fetal neurology training has been implemented in many countries. Pediatric neurologists are asked to examine the data available and to contribute to the definition of the long-term outcomes. Ventriculomegaly, posterior fossa malformations, and agenesis/dysgenesis of corpus callosum are among the most common reasons for antenatal neurological consultations. Fetuses with central nervous system and extra-CNS anomalies should ideally be managed in secondary/tertiary hospitals where obstetricians who are experts in fetal medicine and pediatric specialists are available. Obstetricians play a critical role in screening, performing detailed neurosonography, and referring to other specialists for additional investigations. Clinical geneticists are frequently asked to propose diagnostic tests and counsel complex fetal malformations whose phenotypes may differ from those during postnatal life. Advances in fetal MRI and genetic investigations can support the specialists involved in counseling. Nevertheless, data interpretation can be challenging, and it requires a high level of expertise in a multidisciplinary setting. Postnatally, child neurologists should be part of an integrated multidisciplinary follow-up, together with neonatologists and pediatricians. The neurodevelopmental outcomes should be assessed at least up to school age. Children should be evaluated with formal tests of their gross motor, cognitive, language, fine motor/visuo-perceptual skills, and their behavior. In this perspective, fetal neurology can be regarded as the beginning of a long journey which continues with a prolonged, structured follow-up, support to the families, and transition to adult life. A review of the most common conditions is presented, along with the long-term outcomes and a proposal of the neurodevelopmental follow-up of children with CNS malformation which are diagnosed in uterus.