Disorders of prosencephalic development

Holoprosencephaly spectrum: an up-to-date overview of classification, genetics and neuroimaging

Holoprosencephaly (HPE) is a complex forebrain congenital malformation with widely variable outcomes. It represents a disorder of ventral induction, which begins in the fifth gestational week. Its main feature is forebrain cleavage failure, which prevents the brain complete division into right and left hemispheres, the normal development of midline structures, and the deep brain structure. Based on the severity of prosencephalic cleavage failure, three classic forms (lobar, semilobar, and alobar) were described, and subsequently, interhemispheric variant (syntelencephaly) and septopreoptic variants were proposed. This review proposes a practical imaging approach to diagnosing HPE spectrum disorders, allowing an easier recognition and earlier diagnosis, which is essential for prenatal care and adequate parental counseling. In addition, we intend to simplify the understanding of HPE through a didactic discussion, schematic illustrations, and descriptions of each entity's current classification and critical neuroimaging features, as well as the main differential diagnosis of HPE.

Prenatal Imaging of Supratentorial Fetal Brain Malformation

This review article provides a comprehensive overview of fetal MR imaging in supratentorial cerebral malformations. It emphasizes the importance of fetal MR imaging as an adjunct diagnostic tool used alongside ultrasound, improving the detection and characterization of prenatal brain abnormalities. This article reviews a spectrum of cerebral malformations, their MR imaging features, and the clinical implications of these findings. Additionally, it outlines the growing importance of fetal MR imaging in the context of perinatal care.

Fetal agenesis of the corpus callosum: Clinical and genetic analysis in a series of 40 patients

OBJECTIVES

This study aimed to explore the genetic causes of agenesis of the corpus callosum (ACC) and assess the utility of karyotype analysis, copy number variation sequencing (CNV-seq), and whole-exome sequencing (WES) to genetically diagnose fetal ACC.

METHODS

We retrospectively examined 40 fetuses diagnosed with ACC who underwent prenatal ultrasonography or magnetic resonance imaging between January 2019 and October 2023. Genetic tests were conducted on the fetuses using karyotype analysis or CNV-seq as the first-line diagnosis. WES was performed if aneuploid and pathogenic CNVs were excluded.

RESULTS

Among the 40 fetuses, 29 (72 %) had non-isolated ACC and 11 (28 %) had isolated ACC. Cerebellar dysplasia and hydrocephalus were the most common abnormal developments in the central nervous system. Twenty-eight patients underwent karyotype analysis, with a detection rate of 14 % (4/28). Twenty-six patients underwent CNV-seq; three patients were found to have pathogenic CNVs, with a detection rate of 12 % (3/26). Thirty-three fetuses with no findings of karyotype analysis or CNV-seq were subsequently tested using WES, with a detection rate of 36 % (12/33). Overall, the total diagnostic yield was 48 % (19/40), and monogenic etiology accounted for 30 % (12/40). The genetic detection rate of fetal non-isolated ACC (62 %, 18/29) was higher than that of isolated ACC (9 %, 1/11).

CONCLUSION

Prenatal genetic analysis of fetuses with ACC is clinically significant, with monogenic disorders being the main cause. WES may enhance the detection rate of fetuses with ACC with negative karyotype analysis or CNV-seq results.

Anomalies of the Corpus Callosum in Prenatal Ultrasound: A Narrative Review for Diagnosis and Further Counseling

The corpus callosum is the major interhemispheric tract that plays an important role in neurological function. Understanding the etiology and embryology development helps the ultrasound diagnosis for disorders of the corpus callosum and further counseling. The nonvisualization of cavum septum pellucidum or dysmorphic cavum septum pellucidum in axial view are indirect signs for beginners to diagnose complete agenesis of corpus callosum (cACC) and partial agenesis of the corpus callosum (pACC). Further coronal view, sagittal view, and fetal magnetic resonance imaging are also important for evaluation. Genetic testing plays an essential tool in anomalies of corpus callosum by revealing the underlying genetic pathophysiology, such as chromosomal anomalies and numerous monogenetic disorders in 30%-45% of ACC. Diagnosis and prediction of prognosis for hypoplasia or hyperplasia of the corpus callosum are more difficult compared to cACC and pACC because of the limited reports in the literature. However, the complex types often had poorer prognostic outcomes compared to the isolated types. Hence, it is important to evaluate and follow fetal conditions thoroughly to rule out intracranial or extracranial anomalies in other systems.

Holoprosencephaly: The Disease and Its Related Disabilities

Holoprosencephaly (HPE), the most prevalent developmental anomaly affecting the forebrain in humans, occurs in approximately 1 in 16,000 liveborn neonates, with an incidence reaching 1 in 250 in conceptuses. This condition is distributed worldwide. HPE is etiologically heterogeneous, and its pathogenesis is variable. Environmental, teratogenic, genetic, or metabolic factors can contribute to the development of HPE. Notably, maternal insulin-dependent diabetes mellitus and maternal alcoholism are among the primary causative factors. HPE may be linked to various well-defined multiple malformation syndromes characterized by a normal karyotype, such as Smith–Lemli–Opitz's, Pallister–Hall's, or velocardiofacial syndrome. Alternatively, it can be associated with chromosomal abnormalities. (i.e., Patau's syndrome and, less frequently, Edwards' syndrome or Down's syndrome). The major genes implicated in HPE are SHH, ZIC2, SIX3, and TGIF. The range of HPE is extensive, covering diverse neuropathological phenotypes of varying severity. Three classical types of HPE can be distinguished in increasing order of severity: lobar HPE, characterized by separated right and left ventricles with some continuity across the frontal cortex; semilobar HPE, featuring a partial separation; and the most severe form, alobar HPE, where there is a single brain ventricle and the absence of an interhemispheric fissure. Additionally, there are other variations of HPE, ranging in severity, including the less severe interhemispheric median HPE (also known as middle interhemispheric variant). The phenotypic spectrum of HPE is highly extensive, encompassing severe cerebral malformations to microforms. Children with HPE often encounter numerous medical challenges; among them neurological disorders, craniofacial malformations, endocrine disorders, oral and motor dysfunction, and dysfunction of the autonomic nervous system. Neurologic problems, such as cerebral palsy and seizures, are common. The diagnosis of HPE is typically made prenatally, relying primarily on ultrasound and magnetic resonance imaging examinations. The prognosis for individuals with HPE is largely dependent on its underlying causes. Those with cytogenetic abnormalities, in particular, face a significantly poorer prognosis, with only 2% surviving beyond 1 year.

Fetal MRI Analysis of Corpus Callosal Abnormalities: Classification, and Associated Anomalies

BACKGROUND

Corpus callosal abnormalities (CCA) are midline developmental brain malformations and are usually associated with a wide spectrum of other neurological and non-neurological abnormalities. The study aims to highlight the diagnostic role of fetal MRI to characterize heterogeneous corpus callosal abnormalities using the latest classification system. It also helps to identify associated anomalies, which have prognostic implications for the postnatal outcome.

METHODS

In this study, retrospective data from antenatal women who underwent fetal MRI between January 2014 and July 2023 at Rush University Medical Center were evaluated for CCA and classified based on structural morphology. Patients were further assessed for associated neurological and non-neurological anomalies.

RESULTS

The most frequent class of CCA was complete agenesis (79.1%), followed by hypoplasia (12.5%), dysplasia (4.2%), and hypoplasia with dysplasia (4.2%). Among them, 17% had isolated CCA, while the majority (83%) had complex forms of CCA associated with other CNS and non-CNS anomalies. Out of the complex CCA cases, 58% were associated with other CNS anomalies, while 8% were associated with non-CNS anomalies. 17% of cases had both.

CONCLUSION

The use of fetal MRI is valuable in the classification of abnormalities of the corpus callosum after the confirmation of a suspected diagnosis on prenatal ultrasound. This technique is an invaluable method for distinguishing between isolated and complex forms of CCA, especially in cases of apparent isolated CCA. The use of diffusion-weighted imaging or diffusion tensor imaging in fetal neuroimaging is expected to provide further insights into white matter abnormalities in fetuses diagnosed with CCA in the future.

Clinical Practice Guidelines and Recommendations by the World Association of Perinatal Medicine and Perinatal Medicine Foundation: Reporting Suspected Findings from Fetal Central Nervous System Examination

These guidelines follow the mission of the World Association of Perinatal Medicine, in collaboration with the Perinatal Medicine Foundation, which brings together groups and individuals worldwide, with the aim to improve prenatal detection of central nervous system anomalies and the appropriate referral of pregnancies with suspected fetal anomalies. In addition, this document provides further guidance for healthcare practitioners with the goal of standardizing the description of ultrasonographic abnormal findings.

Tela-choroidea-to-anterior-cerebral-artery distance (TACAD): novel marker on color Doppler to identify fetuses with complete or partial agenesis of corpus callosum

OBJECTIVES

To assess objectively the course of the anterior cerebral artery (ACA) by measuring its distance to the tela choroidea in the midsagittal view, and to compare this distance in normal fetuses with that in those with agenesis of the corpus callosum (ACC), a condition known to be associated with an abnormal course of the ACA.

METHODS

The tela-choroidea-to-anterior-cerebral-artery distance (TACAD) was measured in the midsagittal view of the brain on color Doppler, between the anterior border of the tela choroidea and the ACA at the level of the callosal genu. Reference ranges in relation to gestational age were established in a prospective, cross-sectional study of 253 normal healthy fetuses between 19 and 36 weeks of gestation. The study group included fetuses with complete ACC (n = 28) or partial ACC (n = 18).

RESULTS

TACAD of normal fetuses showed an increase during the second half of pregnancy, with a mean value of 10.1 mm and 14.2 mm at 22 and 30 weeks of gestation, respectively. All (28/28) fetuses with complete ACC and 83% (15/18) of those with partial ACC had significantly shorter TACAD, with mean values of 3.9 mm and 6.6 mm, respectively.

CONCLUSIONS

TACAD is a measurement that is simple to obtain during fetal color Doppler neurosonography, which enables quantification of the course of the ACA and pericallosal artery. TACAD is shorter in fetuses with complete or partial ACC than in normal fetuses and provides an objective, quantifiable value, rather than merely descriptive information. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Holoprosencephaly: Review of Embryology, Clinical Phenotypes, Etiology and Management

Holoprosencephaly (HPE) is the most common malformation of the prosencephalon in humans. It is characterized by a continuum of structural brain anomalies resulting from the failure of midline cleavage of the prosencephalon. The three classic subtypes of HPE are alobar, semilobar and lobar, although a few additional categories have been added to this original classification. The severity of the clinical phenotype is broad and usually mirrors the radiologic and associated facial features. The etiology of HPE includes both environmental and genetic factors. Disruption of sonic hedgehog (SHH) signaling is the main pathophysiologic mechanism underlying HPE. Aneuploidies, chromosomal copy number variants and monogenic disorders are identified in a large proportion of HPE patients. Despite the high postnatal mortality and the invariable presence of developmental delay, recent advances in diagnostic methods and improvements in patient management over the years have helped to increase survival rates. In this review, we provide an overview of the current knowledge related to HPE, and discuss the classification, clinical features, genetic and environmental etiologies and management.

Delineating septo-optic dysplasia

BACKGROUND

Septo-optic dysplasia (SOD), once a variable triad of septum pellucidum defects (SPDs), optic nerve hypoplasia (ONH), and hypopituitarism, has had multiple findings added, with uncertain causes, definitions, and limits.

METHOD

Literature review.

RESULTS

SOD is a complex vascular sequence with confounders.

CONCLUSIONS

Proximal anterior cerebral artery trunk disruptions cause overlapping primary effects, giving ONH alone most often, and isolated SPD less. ONH disruptions can spread to pituitary, SPD disruptions to the cerebral cortex, causing schizencephaly and related anomalies. Pituitary defects are rare without ONH, and cortical findings are rare without SPD. Extensions are unidirectional, so isolated pituitary or cortical defects are separate from SOD. Micro- an- ophthalmia, a suggested ONH variant, is not part of SOD. Disruption by-products can affect development, causing cognitive and endocrine issues, and structural anomalies such as corpus callosum thinning, ventriculomegaly, and hippocampal and olfactory findings. Limbic extensions may also contribute to the same structural defects as by-products. Midline CNS developmental anomalies can act as disruptive foci, most likely through vascular variants, but have separate pathogenesis. Relative frequencies of specific pituitary hormone defects change as SOD rates increase. Increasing relative rates of midline CNS developmental defects and cortical anomalies are consistent with rising levels of exogenous exposures sensitizing to midline predispositions.

Fetal Brain Development: Regulating Processes and Related Malformations

This paper describes the contemporary state of knowledge regarding processes that regulate normal development of the embryonic–fetal central nervous system (CNS). The processes are described according to the developmental timetable: dorsal induction, ventral induction, neurogenesis, neuronal migration, post-migration neuronal development, and cortical organization. We review the current literature on CNS malformations associated with these regulating processes. We specifically address neural tube defects, holoprosencephaly, malformations of cortical development (including microcephaly, megalencephaly, lissencephaly, cobblestone malformations, gray matter heterotopia, and polymicrogyria), disorders of the corpus callosum, and posterior fossa malformations. Fetal ventriculomegaly, which frequently accompanies these disorders, is also reviewed. Each malformation is described with reference to the etiology, genetic causes, prenatal sonographic imaging, associated anomalies, differential diagnosis, complimentary diagnostic studies, clinical interventions, neurodevelopmental outcome, and life quality.

Sonography of fetal holoprosencephaly: a guide to recognize the lesser varieties

BACKGROUND

Alobar holoprosencephaly (HPE) is easily detected during a first-trimester screening examination, conversely, recognizing the lesser varieties may be difficult even in the second trimester.

OBJECTIVES

To describe the imaging findings of a cohort of fetuses with holoprosencephaly (HPE) and to elucidate the appearances of the different anatomical varieties.

MATERIALS AND METHODS

We reviewed medical records and stored images of pregnant women referred to our clinic because of a diagnosis or the suspicion of various forms of HPE. We reported the imaging characteristics, the presence of other associated anomalies, magnetic resonance findings, karyotype and autoptic examinations when available.

RESULTS

Alobar forms show great distortion of normal brain anatomy, with a single ventricle detectable during the first trimester of pregnancy. Extracerebral, face and karyotype abnormalities are often associated. In semilobar and lobar forms the septum pellucidum is typically absent in axial planes, with fused frontal horns, while posterior fossa is often normal. At multiplanar neurosonogram, anomalies involving corpus callosum and cortex development can be detected. Face abnormalities are mild in lobar forms: receding forehead, various degrees of hypotelorism and the presence of a single central maxillary incisor are reported.

CONCLUSIONS

The alobar forms are detectable since the first trimester, with a peculiar single ventricle and extremely frequent extracerebral and karyotype abnormalities. The semilobar and lobar forms are more challenging and the diagnosis is easily missed in a mid-trimester screening exam unless a careful evaluation of both cavum septi pellucidi and frontal horns as well is conducted.

Alobar holoprosencephaly in an aborted American Quarter Horse fetus

Holoprosencephaly is a central nervous system malformation, characterized by incomplete or total lack of division of prosencephalon hemispheres, which is commonly accompanied by craniofacial malformations. A 9-month-gestation aborted American Quarter Horse fetus was submitted for postmortem examination. The fetus lacked haircoat and had severe facial malformations including marked shortening/absence of the maxillary, incisive and nasal bones, bilateral anophthalmia, and pre-maxillary agenesis. The prosencephalon was small and nearly spherical, represented by a single lobe, with no visible separation between cerebral hemispheres. The olfactory bulbs, piriform lobes, and the optic chiasm were absent. At cross-sectioning of the prosencephalon, the inner structures of the brain were completely absent, and replaced by a monoventricle lined by the remaining compressed cortex, and the thalami were fused. Since mutations in the sonic hedgehog (SHH) gene have been associated with human holoprosencephaly, the three coding SHH exons were sequenced using liver DNA of the aborted foal. The obtained SHH sequence was similar to the Equus caballus SHH mRNA sequence deposited in Genbank^TM (XM_023640069.1); therefore, no polymorphism in the coding region of this gene justifying the phenotype was observed. This is the first report of alobar holoprosencephaly in horses.

Disorders of Neuronal Migration/Organization Convey the Highest Risk of Neonatal Onset Epilepsy Compared With Other Congenital Brain Malformations

BACKGROUND

Although seizures in neonates are common and often due to acute brain injury, 10-15% are unprovoked from congenital brain malformations. A better understanding of the risk of neonatal-onset epilepsy by the type of brain malformation is essential for counseling and monitoring.

METHODS

In this retrospective cohort study, we evaluated 132 neonates with congenital brain malformations and their risk of neonatal-onset epilepsy. Malformations were classified into one of five categories based on imaging patterns on prenatal or postnatal imaging. Infants were monitored with continuous video EEG (cEEG) for encephalopathy and paroxysmal events in addition to abnormal neuroimaging.

RESULTS

Seventy-four of 132 (56%) neonates underwent EEG monitoring, and 18 of 132 (14%) were diagnosed with neonatal-onset epilepsy. The highest prevalence of epilepsy was in neonates with disorders of neuronal migration/organization (9/34, 26%; 95% confidence interval [CI] = 13-44%), followed by disorders of early prosencephalic development (6/38, 16%; 95% CI = 6-31%), complex total brain malformations (2/16, 13%; 95% CI = 2-38%), and disorders of midbrain/hindbrain malformations (1/30, 3%; 95% CI = 0-17%). Of neonates with epilepsy, 5 of 18 (28%) had only electrographic seizures, 13 of 18 (72%) required treatment with two or more antiseizure medicines (ASMs), and 7 of 18 (39%) died within the neonatal period.

CONCLUSION

Our results demonstrate that disorders of neuronal migration/organization represent the highest-risk group for early-onset epilepsy. Seizures are frequently electrographic only, require treatment with multiple ASMs, and portend a high mortality rate. These results support American Clinical Neurophysiology Society recommendations for EEG monitoring during the neonatal period for infants with congenital brain malformations.

The diagnosis of the middle interhemispheric variant of holoprosencephaly with fetal MRI

Congenital anomalies of the central nervous system comprise a wide spectrum of malformations associated with a wide variety of genetic syndromes and chromosomal anomalies, and they are among the principal causes of morbidity and mortality in infants. Among these anomalies, holoprosencephaly arises from the complete or partial failure of the brain to divide into the cerebral hemispheres. Imaging tests are fundamental for the prenatal diagnosis of holoprosencephaly; the diagnostic process usually starts with sonography and then the findings are refined with fetal MRI. Radiologists need to be familiar with the possible findings because the prognosis varies.

Prenatal diagnosis of middle interhemispheric variant of holoprosencephaly: review of literature and prenatal case series

OBJECTIVE

Middle interhemispheric (MIH) variant of holoprosencephaly (HPE) or syntelencephaly is a rare prosencephalic cleavage disorder. In literature, few cases of accurate prenatal diagnosis have been reported. We report on four additional prenatally diagnosed cases.

METHODS

Between 2012 and 2017, four cases of MIH HPE were retrieved. Data on prenatal imaging, genetic analysis, and pathological investigation are collected. A "PubMed" and "Trip database" search were conducted revealing six papers reporting on 11 prenatally diagnosed cases.

RESULTS AND DISCUSSION

Four additional cases of MIH HPE were diagnosed at an earlier gestational age (between 17 and 25 weeks of gestation) compared with 11 cases from the literature review (15-39 weeks). First trimester transvaginal ultrasound facilitates correct differentiation between the severe HPE variants. Frequent association with ZIC2 mutation was found in nearly 50% of the cases (5/11) compared with one case in our series.

CONCLUSIONS

MIH variant of HPE is detectable from the early second trimester and should be considered in the differential diagnosis when the cavum septi pellucidi (CSP) is absent. Genetic analysis and autopsy should be conducted to investigate this more recent and rare variant.

K, A. S, K. N. Persistent Fetal Trigeminal Artery with Septopreoptic Holoprosencephaly: Report of an Unusual Association

Septopreoptic holoprosencephaly (HPE) is a type of HPE characterized by failure of separation of the septal and preoptic regions. Vascular anomalies associated with septopreoptic HPE include twig-like cerebral vessels and azygos anterior cerebral artery, the latter common to all forms of HPE. Here, we describe an 8-year-old boy presenting with developmental delay and abnormal movements who was found to have septopreoptic HPE associated with persistent trigeminal artery in magnetic resonance neuroimaging. This persistence of fetal trigeminal artery in HPE provides a further understanding of the pathogenesis of HPE.

Novel and recurrent variants identified in fetuses with central nervous system abnormalities by trios-medical exome sequencing

BACKGROUND

Fetal central nervous system abnormalities often associated with infant death or severe disability. The etiology in fetuses with CNS abnormalities who have normal karyotypes and copy number variants (CNVs) remains unclear, which increases the difficulty in following management and the assessment of prognosis.

METHOD

11 unrelated fetuses with CNS abnormalities and their parents were enrolled. Genomic DNA was obtained and then trios-medical exome sequencing (trios-MES) including 4000 genes (fetuses and their parents) was performed after both karyotyping and chromosome microarray showed negative results.

RESULTS

Pathogenic and likely pathogenic variants were identified in five of 11 cases (5/11, 45.5%), including five novel mutations and two recurrent mutations in ISPD, L1CAM, and GRIN2B genes. Most cases (4/5, 80%) carried one or two recessive mutations, indicating a high recurrent risk.

CONCLUSION

Exome sequencing should be considered for fetuses with CNS abnormalities following negative results of karyotyping and chromosome array. Trios-MES as one of exome sequencing is a potential method for the diagnosis of these fetuses.

Nationwide epidemiological survey of holoprosencephaly in Japan

BACKGROUND

Holoprosencephaly (HPE) is a congenital malformation with an estimated prevalence of 0.10-6.06 per 10 000 births but with no nationwide data specific to Japan.

METHODS

This nationwide retrospective questionnaire survey was conducted from 2011 to 2013. All 467 training hospitals for perinatal and neonatal care certified by the Japan Society of Perinatal and Neonatal Medicine were contacted. The birth prevalence rate (BPR) was assessed from the primary survey and clinical characteristics from the secondary survey.

RESULTS

We received valid responses from 253 hospitals in the primary survey (54.6%). Of 390 342 live births, 60 were diagnosed with HPE (23 males and 37 females), resulting in an actual BPR of 1.54 per 10 000 live births. The point estimate for HPE cases was 100 (95% confidence interval [CI]: 80.7-120), and the estimated BPR of HPE was calculated to be 0.32 per 10 000 live births (95% CI: 0.26-0.38) based on 3 117 853 live births according to Japanese national statistics during the study period. In the secondary survey, we obtained data for 49 cases (19 males and 30 females). Of these, 20 were alobar (40.8%), 20 were semilobar (40.8%), five were lobar (10.4%), and four were of unknown type. Genetic examination was performed in 37 of the 49 HPE patients and revealed that chromosomes 13, 18, and 7 were affected in eight, six, and four patients, respectively.

CONCLUSIONS

This is the most extensive survey on holoprosencephaly to date in Japan. The estimated BPR was consistent with that reported in previous research.

Lobar holoprosencephaly with craniofacial defects in a Friesian calf: A case report

BACKGROUND

Holoprosencephaly is a forebrain deformity that results from varying degrees of separation failure of cerebral hemispheres. The condition is classified based on the degree of non-separation of the hemispheres which, in turn, determines its severity. Holoprosencephaly is usually accompanied by craniofacial defects whose severity tends to reflect the extent of brain deformities. In humans, holoprosencephaly is one of the commonest congenital brain anomalies but in animals, reported cases are scarce. The condition has multifactorial aetiology that involves interactions between several genetic and environmental factors.

CASE PRESENTATION

A 4-day-old female Friesian calf with a deformed face was reported to the Faculty of veterinary medicine and surgery, Egerton University. The calf and the dam were sired by the same bull. On clinical and radiographic examination, the calf had a short snout that curved dorsally with bilateral cleft lip, right-sided cleft jaw and a largely absent primary palate. Anatomopathological examination revealed brain deformities which included ventral fusion of frontal lobes of cerebral hemispheres, large merged lateral ventricles without septum pellucidum and fornix, hypoplastic corpus callosum, high degree of non-separation between diencephalic structures, poorly developed hippocampal formation and hypoplastic olfactory lobe, optic chiasma, and nerve.

CONCLUSION

The case was confirmed as lobar holoprosencephaly based on characteristic anatomopathological findings. The aetiology of the defects in the present case could not be determined though they are thought to be either a result of recessive inheritance or exposure to teratogenic steroid alkaloids through materials fed to the dam during early pregnancy.

Fetal midline anomalies: Diagnosis and counselling Part 1: Corpus callosum anomalies

Midline anomalies encompasses a heterogeneous group of conditions caused by an abnormal process of ventral induction after the end of primary neurulation. Advances in prenatal imaging techniques have led to an increase in the detection rate of such anomalies since the first trimester of pregnancy although a significant proportion of them remain undiagnosed until birth. Ultrasound is the primary technique in detecting such anomalies while fetal magnetic resonance imaging (MRI) is commonly performed to confirm the diagnosis and detect additional anomalies, especially those involving the cortical surface of the brain, which may potentially impact post-natal outcome. Neurodevelopmental outcome of cerebral anomalies involving the midline is directly related to the type of anomaly, cause and presence of associated anomalies. However, even in case of isolated anomalies prenatal counselling is challenging. The aim of this review is to provide an up to date on the diagnosis, counselling and management of the most common supra-tentorial anomalies involving the midline and diagnosed on prenatal ultrasound.

Current state of MRI of the fetal brain in utero

In this article we provide an overview of fetal brain development, describe the range of more common fetal neuropathology, and discuss the relevance of in utero MR (iuMR). Although ultrasonography remains the mainstay of fetal brain imaging, iuMR imaging is both feasible and safe, but presents several challenges. We discuss those challenges, the techniques employed to overcome them, and new approaches that may extend the clinical applicability of fetal iuMR. Level of Evidence: Technical Efficacy Stage. J. Magn. Reson. Imaging 2019;49:632-646.

Neurodevelopmental outcomes in children with prenatally diagnosed corpus callosal abnormalities

OBJECTIVE

Although corpus callosal abnormalities are among the most common brain malformations detected prenatally, few previous studies have described the neurodevelopmental outcomes of children with this condition. The aim of our study was to evaluate the neurodevelopmental outcomes and associated clinical features of children with corpus callosal abnormalities diagnosed by prenatal ultrasonography.

METHODS

Between July 2011 and July 2016, forty-nine children with corpus callosal abnormalities were born in Asan Medical Center Children's Hospital. Neurodevelopmental assessments were conducted in 40 patients at a median age of 24.8 months using the Bayley Scales of Infant Development II or the Korean Infant and Child Development Test. Patients were categorized according to their postnatal magnetic resonance imaging (MRI) findings and accompanying anomalies. Baseline characteristics and developmental outcomes of each group were compared.

RESULTS

Isolated agenesis or hypoplasia of the corpus callosum was found in 16 (32.7%) patients, other associated central nervous system (CNS) abnormalities were found in 28 (57.1%) patients, and non-CNS abnormalities were found in 11 (22.4%) patients. Among the 40 patients who underwent developmental assessment, 18 (45.0%) showed normal development and 10 (25.0%) showed moderate-to-severe global developmental delay. Seven of the twelve (58.3%) patients with isolated corpus callosal abnormalities showed normal development. The combination of corpus callosal abnormalities with non-CNS anomalies was significantly associated with developmental delay (odds ratio 2.5, 95% confidence interval 1.6-3.9, p = 0.001). Conversely, children with isolated corpus callosal abnormalities showed relatively favorable neurodevelopmental outcomes.

CONCLUSION

Appropriate evaluation and comprehensive therapeutic approaches are strongly recommended for neonates who present with corpus callosal abnormalities combined with additional anomalies.

Nervous System Malformations

PURPOSE OF REVIEW

This article provides an overview of the most common nervous system malformations and serves as a reference for the latest advances in diagnosis and treatment.

RECENT FINDINGS

Major advances have occurred in recognizing the genetic basis of nervous system malformations. Environmental causes of nervous system malformations, such as perinatal infections including Zika virus, are also reviewed. Treatment for nervous system malformations begins prior to birth with prevention. Folic acid supplementation reduces the risk of neural tube defects and is an important part of health maintenance for pregnant women. Fetal surgery is now available for prenatal repair of myelomeningocele and has been demonstrated to improve outcomes.

SUMMARY

Each type of nervous system malformation is relatively uncommon, but, collectively, they constitute a large population of neurologic patients. The diagnosis of nervous system malformations begins with radiographic characterization. Genetic studies, including chromosomal microarray, targeted gene sequencing, and next-generation sequencing, are increasingly important aspects of the assessment. A genetic diagnosis may identify an associated medical condition and is necessary for family planning. Treatment consists primarily of supportive therapies for developmental delays and epilepsy, but prenatal surgery for myelomeningocele offers a glimpse of future possibilities. Prognosis depends on multiple clinical factors, including the examination findings, imaging characteristics, and genetic results. Treatment is best conducted in a multidisciplinary setting with neurology, neurosurgery, developmental pediatrics, and genetics working together as a comprehensive team.

Prenatal diagnosis of holoprosencephaly

Holoprosencephaly is a spectrum of congenital defects of forebrain development characterized by incomplete separation of the cerebral hemispheres. In vivo diagnosis can be established with prenatal brain imaging and disease severity correlates with extent of abnormally developed brain tissue. Advances in magnetic resonance imaging (MRI) over the past 25 years and their application to the fetus have enabled diagnosis of holoprosencephaly in utero. Here, we report on the prenatal diagnosis of holoprosencephaly using MRI as part of a diagnostic and management evaluation at a tertiary and quaternary referral center. Using an advanced MRI protocol and a 1.5-Tesla magnet, we show radiographic data diagnostic for the holoprosencephaly spectrum, including alobar, semilobar, lobar, middle interhemispheric, and septopreoptic variant. Accurate prenatal evaluation is important because the severity of imaging findings correlates with postnatal morbidity and mortality in holoprosencephaly. Therefore, this work has implications for the evaluation, diagnosis, management, and genetic counseling that families can receive during a pregnancy.

Apert syndrome: magnetic resonance imaging (MRI) of associated intracranial anomalies

INTRODUCTION

Apert syndrome is one of the most common craniosynostosis syndrome caused by mutations in genes encoding fibroblast growth factor receptor 2 (FGFR2). It is characterized by multisuture craniosynostosis, midfacial hypoplasia, abnormal skull base development and syndactyly of all extremities. Apert syndrome is associated with a wide array of central nervous system (CNS) anomalies, possibly the cause of the common occurrence of mental deficiency in patients with Apert syndrome. These CNS anomalies can be broadly classified into two groups; (1) those that are primary malformations and (2) those that occur secondary to osseous deformity/malformation.

CONCLUSION

Familiarity with CNS anomalies associated with Apert syndrome is important to both clinicians and radiologist as it impacts on management and prognostication. Cognitive development of patients has been linked to associated CNS anomalies, timing of surgery and social aspects. These associated anomalies can be broadly classified into (1) those that are primary malformations and (2) those that occur secondary to osseous deformity/malformation, as illustrated in our review paper.

Typical lesions in the fetal nervous system: correlations between fetal magnetic resonance imaging and obstetric ultrasonography findings

Central nervous system (CNS) malformations play a role in all fetal malformations. Ultrasonography (US) is the best screening method for identifying fetal CNS malformations. A good echographic study depends on several factors, such as positioning, fetal mobility and growth, the volume of amniotic fluid, the position of the placenta, the maternal wall, the quality of the apparatus, and the sonographer’s experience. Although US is the modality of choice for routine prenatal follow-up because of its low cost, wide availability, safety, good sensitivity, and real-time capability, magnetic resonance imaging (MRI) is promising for the morphological evaluation of fetuses that otherwise would not be appropriately evaluated using US. The aim of this article is to present correlations of fetal MRI findings with US findings for the major CNS malformations.

Semilobarholoprosencephaly - A Dreading Congenital Anomaly

Holoprosencephaly (HPE) is a group of structural abnormalities of brain that is an important cause of childhood mortality and morbidity. They usually occur due to impaired midline cleavage of embryonic forebrain i.e., failure of differentiation of the prosencephalon into the telecephalon and diencephalon. De Myer classified this anomaly ranging from alobar to semilobar and lobar type. It can be associated with microcephaly and midline facial anomalies. We present a case of semilobar holoprosencephaly with corpus callosal agenesis.

Fetal Brain Anomalies Associated with Ventriculomegaly or Asymmetry: An MRI-Based Study

BACKGROUND AND PURPOSE

Fetal lateral ventriculomegaly is a relatively common finding with much debate over its clinical significance. The purpose of this study was to examine the association between ventriculomegaly and asymmetry and concomitant CNS findings as seen in fetal brain MR imaging.

MATERIALS AND METHODS

Fetal brain MR imaging performed for various indications, including ventriculomegaly, with or without additional ultrasound findings, was assessed for possible inclusion. Two hundred seventy-eight cases found to have at least 1 lateral ventricle with a width of ≥10 mm were included in the study. Ventriculomegaly was considered mild if the measurement was 10-11.9 mm; moderate if, 12-14.9 mm; and severe if, ≥15 mm. Asymmetry was defined as a difference of ≥2 mm between the 2 lateral ventricles. Fetal brain MR imaging findings were classified according to severity by predefined categories.

RESULTS

The risk of CNS findings appears to be strongly related to the width of the ventricle (OR, 1.38; 95% CI, 1.08-1.76; P = .009). The prevalence of associated CNS abnormalities was significantly higher (P = .005) in symmetric ventriculomegaly compared with asymmetric ventriculomegaly (38.8% versus 24.2%, respectively, for all CNS abnormalities and 20% versus 7.1%, respectively, for major CNS abnormalities).

CONCLUSIONS

In this study, we demonstrate that the rate of minor and major findings increased with each millimeter increase in ventricle width and that the presence of symmetric ventricles in mild and moderate ventriculomegaly was a prognostic indicator for CNS abnormalities.

Alobar Holoprosencephaly With Cebocephaly

Holoprosencephaly (HPE) is a complex brain malformation caused by incomplete fusion of cleavage of the cerebral hemispheres and deep brain structures affecting 6 to 12:10,000 live-born infants. There are three categories of HPE ranging in severity, with alobar holoprosencephaly being the most severe, followed by semilobar holoprosencephaly, and lobar holoprosencephaly being the mildest form. Facial anomalies as well as chromosome anomalies are often associated with HPE. This case study describes a transabdominal sonographic diagnosis of alobar HPE with cebocephaly originally found at 27 weeks 3 days on a patient with no prenatal care.

Congenital basis of posterior fossa anomalies

The classification of posterior fossa congenital anomalies has been a controversial topic. Advances in genetics and imaging have allowed a better understanding of the embryologic development of these abnormalities. A new classification schema correlates the embryologic, morphologic, and genetic bases of these anomalies in order to better distinguish and describe them. Although they provide a better understanding of the clinical aspects and genetics of these disorders, it is crucial for the radiologist to be able to diagnose the congenital posterior fossa anomalies based on their morphology, since neuroimaging is usually the initial step when these disorders are suspected. We divide the most common posterior fossa congenital anomalies into two groups: 1) hindbrain malformations, including diseases with cerebellar or vermian agenesis, aplasia or hypoplasia and cystic posterior fossa anomalies; and 2) cranial vault malformations. In addition, we will review the embryologic development of the posterior fossa and, from the perspective of embryonic development, will describe the imaging appearance of congenital posterior fossa anomalies. Knowledge of the developmental bases of these malformations facilitates detection of the morphological changes identified on imaging, allowing accurate differentiation and diagnosis of congenital posterior fossa anomalies.

Modeling neurodevelopmental disorders using human pluripotent stem cells

Neurodevelopmental disorders (NDs) are impairments that affect the development and growth of the brain and the central nervous system during embryonic and early postnatal life. Genetically manipulated animals have contributed greatly to the advancement of ND research, but many of them differ considerably from the human phenotype. Cellular in vitro models are also valuable, but the availability of human neuronal cells is limited and their lifespan in culture is short. Human pluripotent stem cells (hPSCs), including embryonic stem cells and induced pluripotent stem cells, comprise a powerful tool for studying developmentally regulated diseases, including NDs. We reviewed all recent studies in which hPSCs were used as in vitro models for diseases and syndromes characterized by impairment of neurogenesis or synaptogenesis leading to intellectual disability and delayed neurodevelopment. We analyzed their methodology and results, focusing on the data obtained following in vitro neural differentiation and gene expression and profiling of the derived neurons. Electrophysiological recording of action potentials, synaptic currents and response to neurotransmitters is pivotal for validation of the neuronal fate as well as for assessing phenotypic dysfunctions linked to the disease in question. We therefore focused on the studies which included electrophysiological recordings on the in vitro-derived neurons. Finally, we addressed specific issues that are critical for the advancement of this area of research, specifically in providing a reliable human pre-clinical research model and drug screening platform.

The ubiquitin E3 ligase NOSIP modulates protein phosphatase 2A activity in craniofacial development

Holoprosencephaly is a common developmental disorder in humans characterised by incomplete brain hemisphere separation and midface anomalies. The etiology of holoprosencephaly is heterogeneous with environmental and genetic causes, but for a majority of holoprosencephaly cases the genes associated with the pathogenesis could not be identified so far. Here we report the generation of knockout mice for the ubiquitin E3 ligase NOSIP. The loss of NOSIP in mice causes holoprosencephaly and facial anomalies including cleft lip/palate, cyclopia and facial midline clefting. By a mass spectrometry based protein interaction screen we identified NOSIP as a novel interaction partner of protein phosphatase PP2A. NOSIP mediates the monoubiquitination of the PP2A catalytic subunit and the loss of NOSIP results in an increase in PP2A activity in craniofacial tissue in NOSIP knockout mice. We conclude, that NOSIP is a critical modulator of brain and craniofacial development in mice and a candidate gene for holoprosencephaly in humans.

Postnatal Diagnosis of a Baby With Multiple Rare Congenital Anomalies Including Syngnathia, Brain Dysmorphism, and Skin Pigmentation

Syngnathia is a rare congenital disorder of jaw fusion with a paucity of literature from developed countries. We present a case of an infant noted to have multiple anomalies at birth including syngnathia, microcephaly with a variant of brain abnormality between holoprosencephaly and syntelencephaly, optic nerve hypoplasia, ear canal anomalies, hemi-vertebrae, and suspected hypomelanosis of Ito. To our knowledge, this patient with syngnathia and multiple anomalies is the first to be reported, but whether they are a coincidence, a pathogenetic association, or a new syndrome remains unknown. This case is discussed with a brief review of the literature.

Hand in glove: brain and skull in development and dysmorphogenesis

The brain originates relatively early in development from differentiated ectoderm that forms a hollow tube and takes on an exceedingly complex shape with development. The skull is made up of individual bony elements that form from neural crest- and mesoderm-derived mesenchyme that unite to provide support and protection for soft tissues and spaces of the head. The meninges provide a protective and permeable membrane between brain and skull. Across evolutionary and developmental time, dynamic changes in brain and skull shape track one another so that their integration is evidenced in two structures that fit soundly regardless of changes in biomechanical and physiologic functions. Evidence for this tight correspondence is also seen in diseases of the craniofacial complex that are often classified as diseases of the skull (e.g., craniosynostosis) or diseases of the brain (e.g., holoprosencephaly) even when both tissues are affected. Our review suggests a model that links brain and skull morphogenesis through coordinated integration of signaling pathways (e.g., FGF, TGFβ, Wnt) via processes that are not currently understood, perhaps involving the meninges. Differences in the earliest signaling of biological structure establish divergent designs that will be enhanced during morphogenesis. Signaling systems that pattern the developing brain are also active in patterning required for growth and assembly of the skull and some members of these signaling families have been indicated as causal for craniofacial diseases. Because cells of early brain and skull are sensitive to similar signaling families, variation in the strength or timing of signals or shifts in patterning boundaries that affect one system (neural or skull) could also affect the other system and appropriate co-adjustments in development would be made. Interactions of these signaling systems and of the tissues that they pattern are fundamental to the consistent but labile functional and structural association of brain and skull conserved over evolutionary time obvious in the study of development and disease.

Molecular genetics in fetal neurology

Brain malformations, particularly related to early brain development, are a clinically and genetically heterogeneous group of fetal neurological disorders. Fetal cerebral malformation, predominantly of impaired prosencephalic development namely agenesis of the corpus callosum and septo-optic dysplasia, is the main pathological feature in fetus, and causes prominent neurodevelopmental retardation, and associated with congenital facial anomalies and visual disorders. Differential diagnosis of brain malformations can be extremely difficult even through magnetic resonance imaging. Advances in genomic and molecular genetics technologies have led to the identification of the sonic hedgehog pathways and genes critical to the normal brain development. Molecular cytogenetic and genetic studies have identified numeric and structural chromosomal abnormalities as well as mutations in genes important for the etiology of fetal neurological disorders. In this review, we update the molecular genetics findings of three common fetal neurological abnormalities, holoprosencephaly, lissencephaly and agenesis of the corpus callosum, in an attempt to assist in perinatal and prenatal diagnosis.

Malformations of cortical development with good clinical outcome: a case report and review of literature

Malformations of cortical development (MCD) are important causes of chronic epilepsy. MCD encompass many varied disorders with diverse clinical manifestations. Schizencephaly, one of the MCD, is known to be complicated by various types of epilepsy, most of which are intractable. We treated a 28-year-old man with epilepsy, characterised by unprovoked generalised tonic-clonic seizures accompanied by MCD. Brain MRI detected multiple malformations including septum pellucidum defect, partial corpus callosum defect, schizencephaly, right hippocampal atrophy, cerebellar atrophy and cerebellum atrophy. 99m Tc-ethylcysteinate dimer single photon emission CT showed decreased cerebral blood flow (CBF), and the morphology of CBF defects overlapped with the anomalous findings on MRI. The clinical outcome of the patient was good despite his severe brain malformations. Although the reason of this discrepancy is unclear, the outcomes of social function and epileptic seizures may be relatively good despite severe MCD in some patients.

Prenatal neurologic anomalies: sonographic diagnosis and treatment

The low prevalence of fetal CNS anomalies results in a restricted level of exposure to, and limited experience for most obstetricians involved in, prenatal ultrasound. Sonographic guidelines for screening the fetal brain in a systematic way may increase the detection rate of fetal CNS anomalies, thus promoting correct referral to tertiary care centers offering patients a multidisciplinary approach to the condition. The aim of this review is to elaborate on the prenatal sonographic diagnosis and outcome of various CNS malformations. Detailed neurosonographic investigation has become available through high-resolution vaginal ultrasound probes and the development of a variety of 3-dimensional (3D) ultrasound modalities, such as ultrasound tomographic imaging. In addition, fetal magnetic resonance imaging is particularly helpful in the detection of gyration and neurulation anomalies, and disorders of the gray and white matter. Isolated mild ventriculomegaly is a rather common finding with good overall outcome. With an increasing diameter of the atria, however, and especially with the presence of associated malformations, long-term neurodevelopmental and behavioral outcome is disturbed in about 15% or more of cases. In view of recent developments in fetal therapy for neural tube defects, there is a clear need for a high level of ultrasound screening, work-up and counseling in tertiary care centers to identify those cases that might benefit from in utero intervention. The failure of prosencephalic midline induction and development results in midline defects ranging from alobar holoprosencephaly to isolated corpus callosum defects. The detection of callosal abnormaties is enhanced by 3D ultrasound, but counseling on neurodevelopmental outcome remains challenging. The Dandy-Walker spectrum includes isolated megacisterna magna, Blake's pouch cyst, hypoplasia of the vermis and Dandy-Walker malformation. Except for complete agenesis of the vermis associated with fourth ventricle cyst formation, data on long-term outcomes for the various conditions is largely lacking. Congenital cytomegalovirus (CMV) results in the highest incidence of children born with, or developing, long-term neurologic conditions. If proof of fetal infection has been delivered, microcephaly, cortical malformations, and intraparenchymal cysts show a strong correlation with poor outcome. Fetuses with CMV-related ultrasound abnormalities might benefit from maternal transplacental treatment. The aneurysm of the vein of Galen, a vascular malformation of the brain, often results in high cardiac output failure. After neonatal arterial embolization, survival is about 50% with normal neurologic development in 36% of cases. Over 50% of intracranial tumors are teratomata, presenting as fast-growing heterogeneous solid-cystic masses with calcifications. Most intracranial hemorrhages are related to the ventricular system, and prognosis is often poor, particularly in cases involving parenchymal and subdural bleeding. Proliferation disorders of the brain are often characterized by microcephaly. Their etiology is heterogeneous and prenatal diagnosis is often made late in gestation.

Neurodevelopment after prenatal diagnosis of isolated agenesis of the corpus callosum: an integrative review

OBJECTIVE

To systematically review published data on the neurodevelopment of children that were diagnosed prenatally with isolated agenesis of the corpus callosum.

STUDY DESIGN

Medline and Scopus searches (1960-July 2011); cross-referencing of retrieved articles.

RESULTS

Sixteen reports (132 cases of apparently isolated agenesis of the corpus callosum) were included in the analysis. The rates of normal outcome, borderline or moderate disability and severe disability were 94/132 (71.2%; 95% confidence interval [CI], 63.0-78.3), 18/132 (13.6%; 95% CI, 8.8-20.5), and 22/132 (15.2%; 95% CI, 10.0-22.2), respectively. Magnetic resonance imaging detected additional cerebral abnormalities in 22.5% (95% CI, 12.3-37.5) of apparently isolated agenesis of the corpus callosum cases. In truly isolated agenesis of the corpus callosum (confirmed by magnetic resonance imaging), the rates of normal neurodevelopment and severe disability were 52/69 (75.4%; 95% CI, 64.0-84.0) and 8/69 (11.6%; 95% CI, 6.0-21.2), respectively.

CONCLUSION

Prenatally diagnosed, isolated agenesis of the corpus callosum is usually associated with a favorable outcome. Larger, prospective series are required, as current data are limited, inconsistent, and prevent subgroup analyses (eg, complete vs partial agenesis of the corpus callosum).

Perfil de habilidades do desenvolvimento em crianças com holoprosencefalia e holoprosencefalia like

OBJETIVO: investigar e comparar o desempenho nas habilidades relacionadas ao desenvolvimento motor, cognitivo, linguístico, de socialização e autocuidados de indivíduos com holoprosencefalia e com holoprosencefalia-like. MÉTODO: participaram deste estudo 20 indivíduos com diagnóstico de holoprosencefalia, na faixa etária de 18 a 72 meses, de ambos os sexos, divididos em 2 grupos. O grupo 1 (G1) composto por 12 indivíduos com sinais clínicos do espectro da holoprosencefalia, e o grupo 2 (G2) com holoprosencefalia-like composto por 8 indivíduos com sinais clínicos do espectro da holoprosencefalia-like. A coleta de dados foi realizada por meio da aplicação do Inventário Portage Operacionalizado que avalia as áreas alvos deste estudo. Para a análise estatística utilizou-se análise descritiva da mediana e dos valores mínimos e máximos e foi aplicado o teste estatístico de Mann Whitney (< 0,05% para significância). RESULTADOS: os grupos 1 e 2 apresentaram alterações em todas as áreas do desenvolvimento avaliadas. Entretanto, os indivíduos do G1, com holoprosencefalia apresentaram maiores comprometimentos nas habilidades: motora, cognitiva, de linguagem, de socialização e autocuidados, quanto comparados aos indivíduos do G2, com holoprosencefalia-like. CONCLUSÃO: o desempenho nas áreas motoras, cognitivas, de linguagem, de socialização e autocuidados de indivíduos com holoprosencefalia e holoprosencefalia-like foi aquém do esperado, principalmente naqueles indivíduos com holoprosencefalia, que se justifica pelo maior comprometimento no sistema nervoso central. A natureza destas alterações pode estar associada ao universo de alterações neurológicas e craniofaciais descritas nestes quadros clínicos e também à influência do ambiente social.

Holoprosencephaly at prenatal diagnosis: analysis of 28 cases regarding etiopathogenic diagnoses

OBJECTIVE

To assess the likelihood of finding an etiopathogenic cause in an ultrasonographic prenatal diagnosis of holoprosencephaly.

MATERIALS AND METHODS

From January 1996 to June 2010, 13 883 prenatal diagnoses through chorionic villus sampling or amniocentesis were made. Every fetus with holoprosencephaly at ultrasound was evaluated. Gestational age, additional ultrasound findings, and fetal karyotype were recorded. Molecular diagnosis and parental karyotype were studied, if relevant.

RESULTS

Twenty-eight fetuses were diagnosed with holoprosencephaly (0.20%). All cases had additional ultrasound findings (100%). A definitive etiology was found in 23 cases (82.14%): karyotype was abnormal in 19 (67.9%) and normal in 8 (28.5%) cases. In the normal karyotype group, although molecular testing was performed in a few cases, one mutation of gene SIX 3 was diagnosed, one diagnosis of dysgnathia complex was made, and two fetuses presented Smith-Lemli-Opitz syndrome. No etiopathogenic diagnosis was made in five fetuses.

CONCLUSIONS

Our results showed that a definitive etiology can be established in most cases of prenatal holoprosencephaly. Chromosomal anomalies were the most frequent finding. However, in euploid fetuses, molecular diagnosis is worthwhile, as different genes with different inheritance patterns may be responsible for this malformation. Thorough evaluation proved beneficial for assessing more accurate prognosis and recurrence risks.