Rhombencephalosynapsis: a hindbrain malformation associated with incomplete separation of midbrain and forebrain, hydrocephalus and a broad spectrum of severity

Partial Rhombencephalosynapsis Presenting in an Adult with Cerebello-Trigeminal-Dermal Dysplasia

Gomez-Lopez-Hernandez syndrome (GLHS), also known as cerebello-trigeminal-dermal dysplasia, is a neurocutaneous disorder typically presenting in childhood. GLHS is characterized by rhombencephalosynapsis (RES) and partial alopecia, with or without trigeminal anesthesia. We describe a rare case of GLHS in a paucisymptomatic adult who presented with new-onset seizure-like activity. Magnetic resonance imaging revealed partial midline fusion of the cerebellar hemispheres, incomplete development of vermis, and slight medialization of the dentate nuclei: all consistent with the diagnosis of RES. Radiographic evidence combined with partial alopecia, truncal ataxia, and muscular hypotonia are suggestive GLHS diagnosis. Our report not only highlights the importance of maintaining GLHS on the differential for new-onset seizure-like activity, but also demonstrates how patients with GLHS may be minimally symptomatic and diagnosed in adulthood.

Lay Summary

The Gomez-Lopez-Hernandez syndrome (GLHS), or cerebellotrigeminal-dermal dysplasia, is a rare condition that affects both the nervous system and the skin. It involves abnormal development of the brain, partial alopecia [thinning of hair], and loss of sensation in the face. One specific brain malformation, called rhombencephalosynapsis (RES), results from abnormal formation of the cerebellum and is seen in GHLS.Both RES and GLHS present early in childhood, and cases presenting later in life are exceptionally rare. Here we describe a young adult with RES and GLHS whose normal development and mild clumsiness eluded recognition by doctors until early adulthood when she presented with a single seizure.

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.

Rhombencephalosynapsis With Obstructive Hydrocephalus: A Rare Presentation of the Cerebellar Anomaly on MRI Findings

Rhombencephalosynapsis is an exceptionally uncommon cerebellar anomaly characterized by the absence or underdevelopment of vermal axons, the presence of dentate nuclei, and the fusion of cerebral hemispheres. Depending on the presence or absence of additional supratentorial anomalies, the prognosis and clinical appearance can vary widely. Here, we present the case of a consanguineous-parent newborn boy, aged four days, who was diagnosed with the use of an MRI. The child had spastic diplegia, bone anomalies, and facial dysmorphism. Slight hydrocephalus, hypogenesis of the corpus callosum, and agenesis of the septum pellucidum were some of the additional supratentorial abnormalities. This study details the clinical and MRI findings, as well as a possible etiology, of this illness.

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.

Applicability of a semiautomated volumetric approach (5D CNS+™) for detailed antenatal reconstruction of abnormal fetal CNS anatomy

BACKGROUND

The aim of this study was to evaluate the accuracy and reliability of a semiautomated volumetric approach (5D CNS+™) when examining fetuses with an apparent abnormal anatomy of the central nervous system (CNS).

METHODS

Stored 3D volumes extracted from a cohort of > 1.400 consecutive 2nd and 3rd trimester pregnancies (range 15-36 gestational weeks) were analyzed using the semiautomatic software tool 5D CNS+™, enabling detailed reconstruction of nine diagnostic planes of the fetal brain. All 3D data sets were examined and judged for plane accuracy, the need for manual adjustment, and fetal CNS anomalies affecting successful plane reconstruction.

RESULTS

Based on our data of 91 fetuses with structural cerebral anomalies, we were able to reveal details of a wide range of CNS anomalies with application of the 5D CNS+™ technique. The corresponding anatomical features and consecutive changes of neighboring structures could be clearly demonstrated. Thus, a profound assessment of the entire altered CNS anatomy could be achieved in nearly all cases. The comparison with matched controls showed a significant difference in volume acquisition (p < 0.001) and in need for manual adjustment (p < 0.001) but not in the drop-out rates (p = 0.677) of both groups.

CONCLUSION

5D CNS+™ is applicable in the majority of cases with brain lesions and constitutes a reliable tool even if the integrity of the fetal CNS is compromised by structural anomalies. Using volume data that were acquired in identical cutting sections needed for conventional biometry allows for detailed anatomic surveys grossly independent of the examiner's experience.

Congenital Malformations of Cerebellum

Advances in pre and postnatal neuroimaging techniques, and molecular genetics have increased our understanding of the congenital malformation of the brain. Correct diagnosis of these malformations in regards to embryology, and molecular neurogenetics is of paramount importance to understand the inheritance pattern and risk of recurrence. Lesions detected on prenatal imaging require confirmation either with postnatal ultrasound and/or with MR imaging. With the advent of the faster (rapid) MRI techniques, which can be conducted without sedation, MRI is commonly used in the evaluation of congenital malformation of the brain. Based on neuroimaging pattern, the congenital malformations of the posterior fossa are classified into 4 main categories: (a) predominantly cerebellar, (b) cerebellar and brainstem, (c) predominantly brainstem, and (d) predominantly midbrain malformations.

Congenital Brain Malformations: An Integrated Diagnostic Approach

Congenital brain malformations are abnormalities present at birth that can result from developmental disruptions at various embryonic or fetal stages. The clinical presentation is nonspecific and can include developmental delay, hypotonia, and/or epilepsy. An informed combination of imaging and genetic testing enables early and accurate diagnosis and management planning. In this article, we provide a streamlined approach to radiologic phenotyping and genetic evaluation of brain malformations. We will review the clinical workflow for brain imaging and genetic testing with up-to-date ontologies and literature references. The organization of this article introduces a streamlined approach for imaging-based etiologic classification into malformative, destructive, and migrational abnormalities. Specific radiologic ontologies are then discussed in detail, with correlation of key neuroimaging features to embryology and molecular pathogenesis.

Neuroimaging in cerebellar ataxia in childhood: A review

Ataxia is one of the most common pediatric movement disorders and can be caused by a large number of congenital and acquired diseases affecting the cerebellum or the vestibular or sensory system. It is mainly characterized by gait abnormalities, dysmetria, intention tremor, dysdiadochokinesia, dysarthria, and nystagmus. In young children, ataxia may manifest as the inability or refusal to walk. The diagnostic approach begins with a careful clinical history including the temporal evolution of ataxia and the inquiry of additional symptoms, is followed by a meticulous physical examination, and, depending on the results, is complemented by laboratory assays, electroencephalography, nerve conduction velocity, lumbar puncture, toxicology screening, genetic testing, and neuroimaging. Neuroimaging plays a pivotal role in either providing the final diagnosis, narrowing the differential diagnosis, or planning targeted further workup. In this review, we will focus on the most common form of ataxia in childhood, cerebellar ataxia (CA). We will discuss and summarize the neuroimaging findings of either the most common or the most important causes of CA in childhood or present causes of pediatric CA with pathognomonic findings on MRI. The various pediatric CAs will be categorized and presented according to (a) the cause of ataxia (acquired/disruptive vs. inherited/genetic) and (b) the temporal evolution of symptoms (acute/subacute, chronic, progressive, nonprogressive, and recurrent). In addition, several illustrative cases with their key imaging findings will be presented.

Rhomboencephalosynapsis: Review of the literature

Rhombencephalosynapsis is a rare congenital anomaly, characterized by partial or total agenesis of the cerebellar vermis with midline fusion of the cerebellar hemispheres, dentate nuclei, and the superior cerebellar peduncles, creating the distinctive Keyhole appearance of the fourth ventricle. Rhombencephalosynapsis can be isolated or can occur in association with other congenital anomalies and syndromes such as Gómez-López-Hernández Syndrome (GLHS) or VACTERL; vertebral anomalies (V), anal atresia (A), cardiovascular defects (C), esophageal atresia and/or tracheo-esophageal fistula (TE), renal (R) and limb/radial (L) anomalies. Recent advances in prenatal imaging have resulted in an increasing rate of prenatal diagnosis of abnormalities of the posterior fossa including Rhombencephalosynapsis. Patients with rhombencephalosynapsis may present with motor developmental delay, ataxia, swallowing difficulties, muscular hypotonia, spastic quadriparesis, abnormal eye movements and a characteristic "figure-of-eight" head shaking. Cognitive outcome varies from severe intellectual disability to normal intellectual function. Rhombencephalosynapsis with VACTERL is often associated with severe cognitive disabilities, whereas patients with GLHS may have better cognitive function. The most common associated findings with rhombencephalosynapsis include hydrocephalus, mesencephalosynapsis, holoprosencephaly, pontocerebellar hypoplasia, corpus callosum dysgenesis and absence of septum pellucidum. Patients can be categorized into four groups: (1) Rhombencephalosynapsis associated with Gómez-López-Hernández syndrome; (2) Rhombencephalosynapsis with VACTERL; (3) Rhombencephalosynapsis with atypical holoprosencephaly, and (4) isolated rhomboencephalosynapsis. The etiology of rhombencephalosynapsis is unknown. Here, we discuss several hypotheses about its etiology.

Prenatal diagnosis of rhombencephalosynapsis: neuroimaging features and severity of vermian anomaly

OBJECTIVES

To describe the prenatal neuroimaging spectrum of rhombencephalosynapsis (RES) and criteria for its classification according to the severity of vermian anomaly.

METHODS

In this multicenter retrospective study of fetuses with RES between 2002 and 2020, the medical records and brain ultrasound and magnetic resonance images were evaluated comprehensively to determine the severity of the vermian anomaly and the presence of associated brain findings. RES was classified, according to the pattern of vermian agenesis and the extent of the fusion of the hemispheres, as complete RES (complete absence of the vermis) or partial RES (further classified according to the part of the vermis that was missing and, consequently, the region of hemispheric fusion, as anterior, posterior, severe or mixed RES). Findings were compared between cases with complete and those with partial RES.

RESULTS

Included in the study were 62 fetuses with a gestational age ranging between 12 and 37 weeks. Most had complete absence of the vermis (complete RES, 77.4% of cases), a 'round-shaped' cerebellum on axial views (72.6%) and a transverse cerebellar diameter (TCD) < 3^rd centile (87.1%). Among the 22.6% of cases with partial RES, 6.5% were classified as severe partial, 6.5% as partial anterior, 8.1% as partial mixed and 1.6% as partial posterior. Half of these cases presented with normal or nearly normal cerebellar morphology and 28.5% had a TCD within the normal limits. Infratentorially, the fourth ventricle was abnormal in 88.7% of cases overall, and anomalies of the midbrain and pons were frequent (93.5% and 77.4%, respectively). Ventriculomegaly was observed in 80.6% of all cases, being more severe in cases with complete RES than in those with partial RES, with high rates of parenchymal and septal disruption.

CONCLUSIONS

This study provides prenatal neuroimaging criteria for the diagnosis and classification of RES, and identification of related features, using ultrasound and magnetic resonance imaging. According to our findings, a diagnosis of RES should be considered in fetuses with a small TCD (severe cerebellar hypoplasia) and/or a round-shaped cerebellum on axial views, during the second or third trimester, especially when associated with ventriculomegaly. Partial RES is more common than previously thought, but presents an extreme diagnostic challenge, especially in cases with normal or nearly-normal cerebellar morphobiometric features. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

A Proposed Clinical Classification and a Diagnostic Approach for Congenital Ataxias

Purpose of Review

This review proposes a clinical classification for congenital ataxias based on clinical features, neuroimaging, and course of the disease.

Recent Findings

Congenital ataxias are an unusual group of neurologic disorders, with heterogeneous clinical and genetic presentation. Typical clinical features of congenital ataxias include variable degrees of motor developmental delay, very early onset cerebellar ataxia, cognitive impairment, and hypotonia, frequently mistakenly diagnosed as cerebral palsy. Congenital ataxias are usually nonprogressive. Neuroimaging plays an important role in the characterization of congenital ataxias. Despite the development of genetics with exome sequencing, several congenital ataxias remain undetermined, and medical literature on this topic is scarce.

Summary

A didactic classification based on the clinical and neuroimaging features for congenital ataxias include the following 4 main groups: cerebellar malformation, syndromic congenital ataxias, congenital cerebellar hypoplasia, and pontocerebellar hypoplasia. A diagnostic approach for congenital ataxias is proposed, and its differential diagnosis is also discussed.

Neuroendoscopic treatment of symptomatic cyst of the septum pellucidum in children: A case series

BACKGROUND

Symptomatic cysts of the septum pellucidum (CSP) are extremely rare in children and surgical indications are not well defined. A very careful clinical and neuroradiologic evaluation is necessary to consider a patient for surgical indication.

METHODS

We present a surgical series of 7 pediatric patients. Clinical and radiological features of the patients, including clinical presentation, previous treatment, pre, and post-operative MRI, immediate postoperative, neuropsychiatric assessment, and outcomes were reviewed.

RESULTS

There were 5 males and 2 females (mean age 8 yrs). Five patients presented a history of severe intermittent headaches, two of them were admitted with acute symptoms of raised intracranial pressure. One patient presented Epilepsy and ADHD and one patient had severe psychosis. Overall, psychiatric disorders were diagnosed in six patients, three patients had Intellectual Disability (ID). In all cases, the cyst presented a ballooning feature, with a mean volume of 18,36 cm3 (range 10,62-28,5) and significant lateral bulging of both layers. All were operated on endoscopically without complications. After surgery, a very significant decrease in cyst volume was observed (mean volume 5,68 cm3; range 3,18-10,1) with complete disappearance of the ballooning aspect. Headaches resolved in all patients. In two patients operated in emergency papilloedema and vision improved in the first week after surgery. No recurrence of the cysts was noted during follow-up in all patients.

CONCLUSIONS

CSP may be associated with behavioral or psychiatric problems also in children. Neuroendoscopic surgery is a safe and effective therapeutic modality to treat CSP presenting with symptoms and signs of intracranial hypertension with good clinical results.

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.

Imaging spectrum of posterior fossa anomalies on foetal magnetic resonance imaging with an algorithmic approach to diagnosis

Posterior fossa abnormalities are one of the most common indications for performing foetal magnetic resonance imaging (FMRI). Ultrasonography is the initial imaging modality for assessment of foetal posterior fossa. Abnormal findings on ultrasonography warrant further evaluation with FMRI because it offers excellent soft-tissue contrast resolution and multiplanar capabilities. The neurological prognosis of different posterior fossa anomalies varies widely. FMRI plays a crucial role in confirming the diagnosis, assessing the prognosis, and counselling patients regarding continuation of pregnancy and possible post-natal developmental outcome. In this review we present the imaging spectrum of posterior fossa anomalies that readers can encounter in practice, highlight salient points in favour of each diagnosis, and provide a simplified algorithmic approach to reach the final diagnosis.

Verbal Adynamia and Conceptualization in Partial Rhombencephalosynapsis and Corpus Callosum Dysgenesis

Verbal adynamia is characterized by markedly reduced spontaneous speech that is not attributable to a core language deficit such as impaired naming, reading, repetition, or comprehension. In some cases, verbal adynamia is severe enough to be considered dynamic aphasia. We report the case of a 40-year-old, left-handed, male native English speaker who presented with partial rhombencephalosynapsis, corpus callosum dysgenesis, and a language profile that is consistent with verbal adynamia, or subclinical dynamic aphasia, possibly underpinned by difficulties selecting and generating ideas for expression. This case is only the second investigation of dynamic aphasia in an individual with a congenital brain malformation. It is also the first detailed neuropsychological report of an adult with partial rhombencephalosynapsis and corpus callosum dysgenesis, and the only known case of superior intellectual abilities in this context.

Diagnostic Approach to Cerebellar Hypoplasia

Cerebellar hypoplasia (CH) refers to a cerebellum of reduced volume with preserved shape. CH is associated with a broad heterogeneity in neuroradiologic features, etiologies, clinical characteristics, and neurodevelopmental outcomes, challenging physicians evaluating children with CH. Traditionally, neuroimaging has been a key tool to categorize CH based on the pattern of cerebellar involvement (e.g., hypoplasia of cerebellar vermis only vs. hypoplasia of both the vermis and cerebellar hemispheres) and the presence of associated brainstem and cerebral anomalies. With the advances in genetic technologies of the recent decade, many novel CH genes have been identified, and consequently, a constant updating of the literature and revision of the classification of cerebellar malformations are needed. Here, we review the current literature on CH. We propose a systematic approach to recognize specific neuroimaging patterns associated with CH, based on whether the CH is isolated or associated with posterior cerebrospinal fluid anomalies, specific brainstem or cerebellar malformations, brainstem hypoplasia with or without cortical migration anomalies, or dysplasia. The CH radiologic pattern and clinical assessment will allow the clinician to guide his investigations and genetic testing, give a more precise diagnosis, screen for associated comorbidities, and improve prognostication of associated neurodevelopmental outcomes.

Pediatric cerebellar malformations: magnetic resonance diagnostic merits and correlation with neurodevelopmental outcome

Background

In spite of having many classifications for pediatric cerebellar malformations (PCMs), no broadly accepted classification is recommended. Associated neurodevelopmental outcomes in children with PCMs remain poorly defined. Neuroimaging is compulsory for the diagnosis of cerebellar malformation and their associated abnormalities. This article emphasizes on the clinical and radiological traits of PCMs. It proposes a radiological classification and a diagnostic approach and assesses whether specific neuroimaging features in patients with PCM correlate with their neurodevelopmental outcomes.

Results

Fifty-eight pediatric patients were classified as follows: The majority of about 51 cases (88%) showed cerebellar hypoplasia and the remaining 7 cases (12%) showed cerebellar dysplasia. Twenty-six patients (45%) remained undiagnosed, while 32 patients (55%) were having a final diagnosis (24% Dandy-Walker malformation (DWM) (n = 14), 7% isolated vermian hypoplasia (n = 4), 7% congenital disorder of glycosylation (CDG) (n = 4), 5% congenital muscular dystrophy (n = 3), 5% congenital cytomegalovirus (CMV) infection (n = 30), 3% rhombencephalosynapsis (n = 2), 2% Lhermitte-Duclos syndrome (n = 1), and 2% DWM with Joubert syndrome (n = 1)). Overall, for the neurodevelopmental outcome, the majority of patients 90% (52/58) had a global developmental delay (GDD) which is a delay in two or more developmental domains. Both motor and language delay represented about 72% (37/58), intellectual disability was present in 59% (34/58), epilepsy in 53% (31/58), ataxic gait in 57% (33/58), attention deficit hyperactivity disorder (ADHD) in 19% (11/58), autism spectrum disorder (ASD) in 17% (10/58), nystagmus and tremors in 15% (9/58), and behavioral changes in 7% (6/58). Most of the children with cerebellar hypoplasia, about 93%, had GDD. Also, patients with PCH associated with a severe GDD, 75% had a language delay, 50% had intellectual and motor delay, and about 25% had epilepsy. However, we observed mild GDD in half of the vermian hypoplasia cases and half of them had a mild fine motor delay.

Conclusions

Magnetic resonance imaging (MRI) of the pediatric brain provides key information to categorize and classify cerebellar malformations. A neurodevelopmental deficit is highly associated with different types of PCMs. Severe GDD was associated with cerebellar and brain stem involvement. However, children with vermis mal-development were likely to have mild GDD. Familiarity with their diagnostic criteria is mandatory for correct diagnosis and prognosis for patients.

Imaging of fetal ventriculomegaly

Fetal ventriculomegaly is the most common central nervous system abnormality detected by prenatal imaging. It has a high association with other anomalies. Etiologies and prognoses for fetal ventriculomegaly range from normal outcomes to significant neurodevelopmental sequelae. In this paper, we review the development, terminology, pathogenesis, imaging and prognosis of fetal ventriculomegaly.

Normal intellectual skills in patients with Rhombencephalosynapsis

OBJECTIVES

Rhombencephalosynapsis (RES) is a very rare cerebellar malformation. Neurodevelopmental outcome of apparently isolated RES remains poorly documented and standardized cognitive assessment, reported in only nine published cases so far, is lacking. Prenatal counselling is challenging considering the uncertain prognosis of isolated RES. The aim of this study was to focus on cognitive and motor outcome of isolated RES with a clinical description of six new cases and a detailed review of the literature.

METHODS

A single-centre retrospective study of all RES patients over a 15-year period. Ataxia and fine motor skills were scored using a five-grade scale, according to the degree of disturbance of daily living. Intelligence Quotient (IQ) was established according to age-related Weschler Intelligence Scales. A systematic literature review included published cases with relevant outcome data.

RESULTS

Six new cases of apparently isolated RES were reported, including three diagnosed in prenatal settings. The onset age for walking was delayed in four patients. Three patients had head shaking and three had a strabismus. One patient had a mild motor disability, one had subtle ataxia that did not impair daily life and four patients had a normal neurological examination at the last visit. Intellectual abilities were normal in all patients (full IQ score from 90 to 142), although three had ADHD. All received standard schooling. Based on these six new cases, as well as cases from 12 publications in the literature, a total of 28 patients with non-syndromic RES were analysed. Concerning motor outcome, 72% had no complaint or minimal impairment, 16% moderate and 12% severe impairment. Concerning cognitive outcome, 68% had normal cognitive skills, 18% borderline intellectual functioning and 14% moderate to severe disability.

MN1 C-terminal truncation syndrome is a novel neurodevelopmental and craniofacial disorder with partial rhombencephalosynapsis

MN1 encodes a transcriptional co-regulator without homology to other proteins, previously implicated in acute myeloid leukaemia and development of the palate. Large deletions encompassing MN1 have been reported in individuals with variable neurodevelopmental anomalies and non-specific facial features. We identified a cluster of de novo truncating mutations in MN1 in a cohort of 23 individuals with strikingly similar dysmorphic facial features, especially midface hypoplasia, and intellectual disability with severe expressive language delay. Imaging revealed an atypical form of rhombencephalosynapsis, a distinctive brain malformation characterized by partial or complete loss of the cerebellar vermis with fusion of the cerebellar hemispheres, in 8/10 individuals. Rhombencephalosynapsis has no previously known definitive genetic or environmental causes. Other frequent features included perisylvian polymicrogyria, abnormal posterior clinoid processes and persistent trigeminal artery. MN1 is encoded by only two exons. All mutations, including the recurrent variant p.Arg1295* observed in 8/21 probands, fall in the terminal exon or the extreme 3' region of exon 1, and are therefore predicted to result in escape from nonsense-mediated mRNA decay. This was confirmed in fibroblasts from three individuals. We propose that the condition described here, MN1 C-terminal truncation (MCTT) syndrome, is not due to MN1 haploinsufficiency but rather is the result of dominantly acting C-terminally truncated MN1 protein. Our data show that MN1 plays a critical role in human craniofacial and brain development, and opens the door to understanding the biological mechanisms underlying rhombencephalosynapsis.

Diagnosis of rhomboencephalosynapsis by MRI in a 5-year-old child

Rhombencephalosynapsis is a rare defect in the development of the cerebellum, characterized by partial or total agenesis of the vermis, with fusion of the cerebellar hemispheres in the midline. It is usually related to Gómez-López-Hernández Syndrome (cerebellar-trigeminal dermal dysplasia) and VACTERL association association (vertebral defects, vascular anomalies, anal atresia, cardiac anomalies, tracheoesophageal fistula with esophageal atresia, renal dysplasia and limb anomalies). A 5-year-old female patient with spastic cerebral palsy and hydrocephalus presented here, neuroimages documented the next features: absence of cerebellar vermis, periventricular leukomalacia, cerebellar tonsils descent and rhombencephalosynapsis. Other important imaging findings and associations in these cases are discussed.

Genetic evaluation including exome sequencing of two patients with Gomez-Lopez-Hernandez syndrome: Case reports and review of the literature

Rhombencephalosynapsis (RES) is a rare congenital anomaly of the hindbrain characterized by fusion of the cerebellar hemispheres, cerebellar peduncles, and dentate nuclei with vermian absence or hypogenesis. This anomaly can be isolated or part of a larger spectrum of cerebral abnormalities. At least 90 cases are described in the literature and it has been associated with VACTERL and Gomez-Lopez-Hernandez syndrome (GLHS). The most common congenital syndrome associated with RES is GLHS, a rare presumed genetic disorder with over 30 cases thus far described in the literature. No genetic cause has been identified for RES or GLHS. We report two probands diagnosed with GLHS based on clinical criteria. Each proband had RES and bi-parietal scalp alopecia as well as neurologic findings and phenotypic features including trigeminal anesthesia, borderline hypertelorism, midface retrusion, and motor delay. Oliginucleotide-SNP microarray on the male proband revealed a 1.05 Mb copy duplication of uncertain clinical significance at 15q21.3 while oligonucleotide-SNP microarray for the female proband did not reveal any abnormalities. Exome sequencing (ES) was performed on both patients and did not identify any variants that could explain the GLHS phenotype. To our knowledge, these are the first two patients with GLHS described in the literature to undergo ES. Both patients had mild neurologic manifestations requiring physical therapy in early life without known diagnostic cause. Patients found to have scalp alopecia or trigeminal anesthesia with gross motor delay should be evaluated for RES or GLHS as well as screened for associated syndromes and have a complete neurodevelopmental evaluation.

Rhombencephalosynapsis: Fused cerebellum, confused geneticists

Rhombencephalosynapsis (RES) is a unique cerebellar malformation characterized by fusion of the cerebellar hemispheres with partial or complete absence of a recognizable cerebellar vermis. Subsets of patients also have other brain malformations such as midbrain fusion with aqueductal stenosis, characteristic craniofacial features (prominent forehead, flat midface, hypertelorism, ear abnormalities), and somatic malformations (heart, kidney, spine, and limb defects). Similar to known genetic brain malformations, the RES cerebellar malformation is highly stereotyped, yet no genetic causes have been identified. Here, we outline our current understanding of the genetic basis for RES, discuss limitations, and outline future approaches to identifying the causes of this fascinating brain malformation.

Subcortical heterotopic gray matter brain malformations: Classification study of 107 individuals

OBJECTIVE

To better evaluate the imaging spectrum of subcortical heterotopic gray matter brain malformations (subcortical heterotopia [SUBH]), we systematically reviewed neuroimaging and clinical data of 107 affected individuals.

METHODS

SUBH is defined as heterotopic gray matter, located within the white matter between the cortex and lateral ventricles. Four large brain malformation databases were searched for individuals with these malformations; data on imaging, clinical outcomes, and results of molecular testing were systematically reviewed and integrated with all previously published subtypes to create a single classification system.

RESULTS

Review of the databases revealed 107 patients with SUBH, the large majority scanned during childhood (84%), including more than half before 4 years (59%). Although most individuals had cognitive or motor disability, 19% had normal development. Epilepsy was documented in 69%. Additional brain malformations were common and included abnormalities of the corpus callosum (65/102 [64%]), and, often, brainstem or cerebellum (47/106 [44%]). Extent of the heterotopic gray matter brain malformations (unilateral or bilateral) did not influence the presence or age at onset of seizures. Although genetic testing was not systematically performed in this group, the sporadic occurrence and frequent asymmetry suggests either postzygotic mutations or prenatal disruptive events. Several rare, bilateral forms are caused by mutations in genes associated with cell proliferation and polarity (EML1, TUBB, KATNB1, CENPJ, GPSM2).

CONCLUSION

This study reveals a broad clinical and imaging spectrum of heterotopic malformations and provides a framework for their classification.

Fetal and neonatal neurogenetics

Disorders of the developing nervous system may be of genetic origin, comprising congenital malformations of spine and brain as well as metabolic or vascular disorders that affect normal brain development. Acquired causes include congenital infections, hypoxic-ischemic or traumatic brain injury, and a number of rare neoplasms. This chapter focuses on the clinical presentation and workup of neurogenetic disorders presenting in the fetal or neonatal period. After a summary of the most frequent clinical presentations, clues from history taking and clinical examination are illustrated with short case reports. This is followed by a discussion of the different tools available for the workup of neurogenetic disorders, including the various genetic techniques with their advantages and disadvantages. The implications of a molecular genetic diagnosis for the patient and family are addressed in the section on counseling. The chapter concludes with a proposed workflow that may help the clinician when confronted with a potential neurogenetic disorder in the fetal or neonatal period.

What cerebellar malformations tell us about cerebellar development

Structural birth defects of the cerebellum, or cerebellar malformations, in humans, have long been recognized. However, until recently there has been little progress in elucidating their developmental pathogenesis. Innovations in brain imaging and human genetic technologies over the last 2 decades have led to better classifications of these disorders and identification of several causative genes. In contrast, cerebellar malformations in model organisms, particularly mice, have been the focus of intense study for more than 70 years. As a result, many of the molecular, genetic and cellular programs that drive formation of the cerebellum have been delineated in mice. In this review, we overview the basic epochs and key molecular regulators of the developmental programs that build the structure of the mouse cerebellum. This mouse-centric approach has been a useful to interpret the developmental pathogenesis of human cerebellar malformations. However, it is becoming apparent that we actually know very little regarding the specifics of human cerebellar development beyond what is inferred from mice. A better understanding of human cerebellar development will not only facilitate improved diagnosis of human cerebellar malformations, but also lead to the development of treatment paradigms for these important neurodevelopmental disorders.

Fetal and neonatal neuroimaging

Magnetic resonance imaging (MRI) can provide detail of the soft tissues of the fetal and neonatal brain that cannot be obtained by any other imaging modality. Conventional T1 and T2 weighted sequences provide anatomic detail of the normally developing brain and can demonstrate lesions, including those associated with preterm birth, hypoxic ischemic encephalopathy, perinatal arterial stroke, infections, and congenital malformations. Specialized imaging techniques can be used to assess cerebral vasculature (magnetic resonance angiography and venography), cerebral metabolism (magnetic resonance spectroscopy), cerebral perfusion (arterial spin labeling), and function (functional MRI). A wealth of quantitative tools, most of which were originally developed for the adult brain, can be applied to study the developing brain in utero and postnatally including measures of tissue microstructure obtained from diffusion MRI, morphometric studies to measure whole brain and regional tissue volumes, and automated approaches to study cortical folding. In this chapter, we aim to describe different imaging approaches for the fetal and neonatal brain, and to discuss their use in a range of clinical applications.

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.

A de novo variant in ADGRL2 suggests a novel mechanism underlying the previously undescribed association of extreme microcephaly with severely reduced sulcation and rhombencephalosynapsis

Extreme microcephaly and rhombencephalosynapsis represent unusual pathological conditions, each of which occurs in isolation or in association with various other cerebral and or extracerebral anomalies. Unlike microcephaly for which several disease-causing genes have been identified with different modes of inheritance, the molecular bases of rhombencephalosynapsis remain unknown and rhombencephalosynapsis presents mainly as a sporadic condition consistent with de novo dominant variations. We report for the first time the association of extreme microcephaly with almost no sulcation and rhombencephalosynapsis in a fœtus for which comparative patient-parent exome sequencing strategy revealed a heterozygous de novo missense variant in the ADGRL2 gene. ADGRL2 encodes latrophilin 2, an adhesion G-protein-coupled receptor whose exogenous ligand is α-latrotoxin. Adgrl2 immunohistochemistry and in situ hybridization revealed expression in the telencephalon, mesencephalon and rhombencephalon of mouse and chicken embryos. In human brain embryos and fœtuses, Adgrl2 immunoreactivity was observed in the hemispheric and cerebellar germinal zones, the cortical plate, basal ganglia, pons and cerebellar cortex. Microfluorimetry experiments evaluating intracellular calcium release in response to α-latrotoxin binding showed significantly reduced cytosolic calcium release in the fœtus amniocytes vs amniocytes from age-matched control fœtuses and in HeLa cells transfected with mutant ADGRL2 cDNA vs wild-type construct. Embryonic lethality was also observed in constitutive Adgrl2^−/− mice. In Adgrl2^+/− mice, MRI studies revealed microcephaly and vermis hypoplasia. Cell adhesion and wound healing assays demonstrated that the variation increased cell adhesion properties and reduced cell motility. Furthermore, HeLa cells overexpressing mutant ADGRL2 displayed a highly developed cytoplasmic F-actin network related to cytoskeletal dynamic modulation. ADGRL2 is the first gene identified as being responsible for extreme microcephaly with rhombencephalosynapsis. Increased cell adhesion, reduced cell motility and cytoskeletal dynamic alterations induced by the variant therefore represent a new mechanism responsible for microcephaly.

Prenatal aqueduct stenosis: Association with rhombencephalosynapsis and neonatal outcome

BACKGROUND AND PURPOSE

To examine prenatal MRI and postnatal imaging in fetuses with congenital aqueductal stenosis (CAS) to determine the frequency of association of rhombencephalosynapsis (RES) and how it may affect neonatal intensive care unit (NICU) course.

MATERIALS AND METHODS

A single center IRB-approved retrospective study of children with CAS was performed. Prenatal MRI, postnatal images, and clinical data were reviewed. Statistical analysis was performed with SAS statistical software package version 9.3.

RESULTS

Aqueduct obstruction was confirmed for all 30 participants. Hydrocephalus required shunting in all but one (97%). Fifteen neonates had CAS with rhomboencephalosynapsis (RES) (50%). Although neonatal course between the two groups was comparable, 53% of CAS with RES neonates required feeding assistance versus 20% in CAS only (P = 0.128). Shunting in the CAS with RES group occurred at average of 6 days of life versus CAS group at 55 days (P = 0.196). Biometry measurements showed a statistically significant decrease in pons antero-posterior diameter in both groups (CAS only P = 0.0049 and CAS with RES P = 0.0003) when compared with norms for gestational age.

CONCLUSION

CAS has a high association with RES. Feeding assistance in the NICU and earlier neurosurgical intervention may be required in patients with CAS who also have RES.

Novel CNS malformations and skeletal anomalies in a patient with Beaulieu-boycott-Innes syndrome

THO/TREX (transcription/export) is a conserved eukaryotic complex that plays a crucial role in gene expression and prevents DNA damage during mitosis and meiosis. In mammals, TREX is essential during embryogenesis, determining stem cell fate specification by regulating posttranscriptional self-renewal and differentiation in several tissues. It is composed of a core called THO, consisting of THOC1, 2, 5, 6, 7, and additional proteins. Bi-allelic mutations in THOC6 have been associated to Beaulieu-Boycott-Innes syndrome (BBIS), a syndromic form of intellectual disability (ID). To date, nine patients harbouring homozygous or compound heterozygous mutations in THOC6 have been reported. Despite the clinical heterogenity and subtle dysmorphic features in some individuals, distinctive facial features are tall forehead, short and upslanting palpebral fissures, deep set eyes, flat philtrum, and malocclusion. Nonlife threatening congenital anomalies are common, including cardiac and renal malformations, anteriorly displaced anus, cryptorchidism in males, submucous cleft palate, and corpus callosum dysgenesis. Affected patients usually have short stature, mild microcephaly, and mild to moderate ID. Here, we describe an Italian patient with BBIS, carrying two compound heterozygous loss-of-function (LoF) variants in THOC6 (c.577C > T, p.R193* and c.792_793delCA, p.V264Vfs*48). In addition to the common phenotype, she displays cerebellar hypoplasia with severe vermian dysgenesis and hydrocephalus due to aqueductal stenosis, multiple skeletal anomalies and hypergonadotropic hypogonadism. Thus, we review the previous cases and discuss the phenotypic spectrum of BBIS, providing further evidence regarding the pivotal role of TREX complex in human development.

Co-occurrence of Gomez-Lopez-Hernandez syndrome and Autism Spectrum Disorder: Case report with review of literature

We report on Gomez-Lopez-Hernandez syndrome (GLHS) in a Caucasian patient, Georgian, 36 months, male, only child born to non-consanguineous parents. There were no similar cases in the family and among close relatives. MRI study confirmed rhombencephalosynapsis (fusion of cerebellar hemispheres in combination with the agenesis of cerebellar vermis) and mild dilation of the lateral ventricles. Other main findings are bilateral parieto-temporal alopecia and brachiturricephaly (broad skull shape and tower-like elongation of the cranium in the vertical axis), low-set posteriorly retracted ears, strabismus (in the right eye), hypotonia (Beighton scale score - 6) and ataxia (trouble maintaining balance). Patient has no signs of trigeminal anesthesia, no recurrent, painless eye infections, corneal opacities and ulcerated wounds on the facial skin and buccal mucosa were observed. Based on the scientific literature we suggest a finding of brachiturricephaly in addition to rhombencephalosynapsis and bilateral alopecia sufficient to put a diagnosis of GLHS. Patient did not speak, disregarded guardians and clinician addressing him, did not make eye contact, was restless and occasionally displayed aggression and self-injurious behavior. These symptoms confirm the earlier diagnosis of Autism Spectrum Disorder (ASD). Therefore, the current study describes a case of co-occurrence of GLHS and ASD.

Congenital Aqueductal Stenosis: Findings at Fetal MRI That Accurately Predict a Postnatal Diagnosis

BACKGROUND AND PURPOSE

Congenital aqueductal stenosis is a common cause of prenatal ventriculomegaly. An accurate diagnosis provides prognostic information and may guide obstetric management. The purpose of this study was to identify specific anatomic findings on prenatal MR imaging that can be used as predictors of congenital aqueductal stenosis.

MATERIALS AND METHODS

Prenatal and postnatal MRIs of fetuses referred to our institution for ventriculomegaly between June 2008 and August 2015 were reviewed. Imaging findings in postnatally confirmed congenital aqueductal stenosis (disease group) were compared with those of ventriculomegaly cases from other causes (control group). Univariate analysis was performed using the Fisher exact test and the Wilcoxon rank test, and multivariate analysis, via the random forest method.

RESULTS

Forty-three cases of ventriculomegaly had a confirmed postnatal diagnosis of congenital aqueductal stenosis. Thirty-two ventriculomegaly cases negative for congenital aqueductal stenosis were included in the control group. Dominant findings associated with an accurate prenatal diagnosis of congenital aqueductal stenosis on multivariate analysis included the following: enlarged inferior third ventricular recesses, enlargement of the lateral ventricles and third ventricle, and an abnormal corpus callosum. Findings that significantly increase the probability of congenital aqueductal stenosis (high positive predictive value) included the following: enlarged third ventricular recesses, aqueduct funneling, hemorrhage in the cerebral aqueduct, ventricular diverticulum, rhombencephalosynapsis, and dystroglycanopathy-related cerebellar dysplasia.

CONCLUSIONS

Our study identified specific characteristics on fetal MR imaging that can be used as predictors of the diagnosis of congenital aqueductal stenosis. Most of these findings are secondary to the obstructive nature of the resulting hydrocephalus. Common associated malformations such as rhombencephalosynapsis and dystroglycanopathies should also increase the suspicion of congenital aqueductal stenosis when present with ventriculomegaly.

Twenty-Five Diagnoses on Midline Images of the Brain: From Fetus to Child to Adult

Midsagittal images of the brain provide a wealth of anatomic information and may show abnormalities that are pathognomonic for particular diagnoses. Using an anatomy-based approach, the authors identify pertinent anatomic structures to serve as a checklist when evaluating these structures. Subregions evaluated include the corpus callosum, pituitary gland and sellar region, pineal gland and pineal region, brainstem, and cerebellum. The authors present 25 conditions with characteristic identifiable abnormalities at midsagittal imaging. Midsagittal views from multiple imaging modalities are shown, including computed tomography, ultrasonography, and magnetic resonance (MR) imaging. Standard MR imaging sequences are shown, as well as fetal MR and sagittal diffusion-weighted images. To demonstrate these conditions, fetal, neonatal, childhood, adolescent, and young adulthood images are reviewed. The differentiation of normal variants is guided by the understanding of anatomy and pathology. When a specific diagnosis is not possible, the authors present information to evaluate differential considerations and discuss when follow-up imaging may be indicated. The authors hope each case will clarify a pertinent differential diagnosis, appropriately guide patient management, and improve understanding of normal anatomy and identification of pathologic entities. It is in these hopes that the authors have presented a checklist of pertinent anatomy and pathologic entities that can build on existing search patterns. Improved confidence and accuracy in the evaluation of midsagittal images will benefit physicians and patients. ^©RSNA, 2018.

Ultrasound and CT of the posterior fossa in neonates

Ultrasound, CT and MRI may all be used in the evaluation of the posterior fossa in neonates depending on the clinical scenario. Ultrasonography is particularly valuable for the evaluation of the neonatal brain because of the lack of ionizing radiation and the ability to perform exams at the bedside and, importantly, advancements in ultrasound technology now allow for diagnostic-quality imaging. While CT is still the initial imaging modality of choice in most neurologic emergencies, in the neonate, ultrasound is the first line in nontraumatic emergencies. The goal of this chapter is to discuss the ultrasound technique for evaluation of the cerebellum, to describe the normal sonographic and CT appearance of posterior fossa and to provide the classical findings of the most common cerebellar abnormalities. While ultrasound is able to accurately diagnosis a majority of cerebellar abnormalities in neonates, subsequent MR imaging remains essential to confirm findings and to detect associated abnormalities.