Fetal cerebellar growth and Sylvian fissure maturation: international standards from Fetal Growth Longitudinal Study of INTERGROWTH-21st Project.

OBJECTIVE: To construct international ultrasound-based standards for fetal cerebellar growth and Sylvian fissure maturation. METHODS: Healthy, well nourished pregnant women, enrolled at < 14 weeks' gestation in the Fetal Growth Longitudinal Study (FGLS) of INTERGROWTH-21st , an international multicenter, population-based project, underwent serial three-dimensional (3D) fetal ultrasound scans every 5 ± 1 weeks until delivery in study sites located in Brazil, India, Italy, Kenya and the UK. In the present analysis, only those fetuses that underwent developmental assessment at 2 years of age were included. We measured the transcerebellar diameter and assessed Sylvian fissure maturation using two-dimensional ultrasound images extracted from available 3D fetal head volumes. The appropriateness of pooling data from the five sites was assessed using variance component analysis and standardized site differences. For each Sylvian fissure maturation score (left or right side), mean gestational age and 95% CI were calculated. Transcerebellar diameter was modeled using fractional polynomial regression, and goodness of fit was assessed. RESULTS: Of those children in the original FGLS cohort who had developmental assessment at 2 years of age, 1130 also had an available 3D ultrasound fetal head volume. The sociodemographic characteristics and pregnancy/perinatal outcomes of the study sample confirmed the health and low-risk status of the population studied. In addition, the fetuses had low morbidity and adequate growth and development at 2 years of age. In total, 3016 and 2359 individual volumes were available for transcerebellar-diameter and Sylvian-fissure analysis, respectively. Variance component analysis and standardized site differences showed that the five study populations were sufficiently similar on the basis of predefined criteria for the data to be pooled to produce international standards. A second-degree fractional polynomial provided the best fit for modeling transcerebellar diameter; we then estimated gestational-age-specific 3rd , 50th and 97th smoothed centiles. Goodness-of-fit analysis comparing empirical centiles with smoothed centile curves showed good agreement. The Sylvian fissure increased in maturation with advancing gestation, with complete overlap of the mean gestational age and 95% CIs between the sexes for each development score. No differences in Sylvian fissure maturation between the right and left hemispheres were observed. CONCLUSION: We present, for the first time, international standards for fetal cerebellar growth and Sylvian fissure maturation throughout pregnancy based on a healthy fetal population that exhibited adequate growth and development at 2 years of age. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Nomograms of the Fetal Sylvian Fissure and Insular Lobe throughout Gestation: A Multicentric, Ultrasonographic Cross-Sectional Study.

INTRODUCTION: Anomalies in cortical development are often associated with an adverse outcome, but prenatal diagnosis is often impeded by the limited knowledge about normal sulci biometries throughout fetal brain development. Our aim was to provide two-dimensional ultrasonographical (2D US) nomograms of the depth of the Sylvian fissure (SF) and insular lobe (IL), as well as of the SF ratio throughout gestation in a large number of fetuses. MATERIALS AND METHODS: This was a prospective cross-sectional study of 329 normal singleton pregnancies. Measurements of the SF, IL, and SF ratio were obtained in a standard transthalamic plane of the fetal head. The SF ratio was defined as SF\SF + IL. All measurements were expressed by regression equations as a function of gestational age (GA) according to the method described by Royston and Wright. The first 38 measurements were repeated twice by 2 examiners to assess the reproducibility through the intraclass correlation coefficient (ICC). RESULTS: A significant correlation was found between GA and SF (r = 0.79; p < 0.0001) as well as IL (r = 0.77; p < 0.0001). Similarly, the SF ratio also showed a significant correlation with GA (r = 0.39; p < 0.0001). When interobserver variability was assessed, ICC was 0.97. CONCLUSIONS: Prenatal 2D US measurements of SF and IL as well as the SF ratio may be feasible and reproducible using a standard view of the fetal head. Our nomograms may be used as a reference for assessing cortical development throughout pregnancy.

Telencephalic Flexure and Malformations of the Lateral Cerebral (Sylvian) Fissure.

After sagittal division of the prosencephalon at 4.5 weeks of gestation, the early fetal cerebral hemisphere bends or rotates posteroventrally from seven weeks of gestation. The posterior pole of the telencephalon thus becomes not the occipital but the temporal lobe as the telencephalic flexure forms the operculum and finally the lateral cerebral or Sylvian fissure. The ventral part is infolded to become the insula. The frontal and temporal lips of the Sylvian fissure, as well as the insula, all derive from the ventral margin of the primitive telencephalon, hence may be influenced by genetic mutations with a ventrodorsal gradient of expression. The telencephalic flexure also contributes to a shift of the hippocampus from a dorsal to a ventral position, the early rostral pole of the hippocampus becoming caudal and dorsal becoming ventral. The occipital horn is the most recent recess of the lateral ventricle, hence most vulnerable to anatomic variations that affect the calcarine fissure. Many major malformations include lack of telencephalic flexure (holoprosencephaly, extreme micrencephaly) or dysplastic Sylvian fissure (lissencephalies, hemimegalencephaly, schizencephaly). Although fissures and sulci are genetically programmed, mechanical forces of growth and volume expansion are proposed to be mainly extrinsic (including ventricles) for fissures and intrinsic for sulci. In fetal hydrocephalus, the telencephalic flexure is less affected because ventricular dilatation occurs later in gestation. Flexures can be detected prenatally by ultrasound and fetal magnetic resonance imaging and should be described neuropathologically in cerebral malformations.

Changes in the CSF fluid pathways in the developing rat fetus with early onset hydrocephalus.

Interest in the factors involved in the abnormal cortical development of the HTx rat fetus have led us to re-examine the structural and morphological changes in the CSF pathways preceding constriction and blockage of the cerebral aqueduct. Histological analysis was carried out on coronal and sagittal sections from HTx and Wistar fetuses. The aqueduct is found to be a broad channel extending from the posterior end of the third ventricle that ends in a blind pouch above the developing cerebellum. The aqueduct drains into the fourth ventricle via a vertically orientated, narrow channel lying between the posterior aspect of the pontine flexure and the anterior surface of the cerebellum. On Day E18 the connecting channel between the aqueduct and the fourth ventricle is blocked by apposition of its walls. 24 hours later the lateral ventricles begin to dilate and the anterior end of the aqueduct is blocked and the connecting channel between the aqueduct and the fourth ventricle reopens. The cause of these sequential changes in the CSF fluid pathways remains speculative.

Subcommissural organ/Reissner's fiber complex: characterization of SCO-spondin, a glycoprotein with potent activity on neurite outgrowth.

In the developing vertebrate nervous system, several proteins of the thrombospondin superfamily act on axonal pathfinding. By successive screening of a SCO-cDNA library, we have characterized a new member of this superfamily, which we call SCO-spondin. This extracellular matrix glycoprotein of 4,560 amino acids is expressed and secreted early in development by the subcommissural organ (SCO), an ependymal differentiation located in the roof of the Sylvian aqueduct. Furthermore, SCO-spondin makes part of Reissner's fiber (RF), a thread-like structure present in the central canal of the spinal cord. This novel protein shows a unique arrangement of several conserved domains, including 26 thrombospondin type 1 repeats (TSR), nine low-density lipoprotein receptor (LDLr) type A domains, two epidermal growth factor (EGF)-like domains, and N- and C-terminal von Willebrand factor (vWF) cysteine-rich domains, all of which are potent sites of protein-protein interaction. Regarding the huge number of TSR, the putative function of SCO-spondin on axonal guidance is discussed in comparison with other developmental molecules of the CNS exhibiting TSR. To correlate SCO-spondin molecular feature and function, we tested the effect of oligopeptides, whose sequences include highly conserved amino acids of the consensus domains on a neuroblastoma cell line B 104. One of these peptides (WSGWSSCSRSCG) markedly increased neurite outgrowth of B 104 cells and this effect was dose dependent. Thus, SCO-spondin is a favorable substrate for neurite outgrowth and may participate in the posterior commissure formation and spinal cord differentiation during ontogenesis of the central nervous system.

MR imaging of the posterior fossa structures of human embryos and fetuses.

There have been few reports on MR imaging of the developing human fetal brain. The aim of this article is to establish a standard atlas of developing fetal brain, focusing in particular on posterior fossa structures. Eighty-eight formalin-fixed embryos and fetuses were examined using 1.5 Tesla MR units. Specimens ranged from Carnegie stage 17 to 28 gestational weeks. The morphologic changes in developing cerebellum, cerebellar fissures, pontine flexure, fourth ventricle, and cerebral aqueduct were observed in each developmental period. The height of the fourth ventricle and cerebral aqueduct and the thickness of the tectum and the tegmentum of the midbrain were measured. We obtained detailed MR images of the developmental changes in posterior fossa structures and produced an atlas of these images. Our study showed that the period of visualization of cerebellar structures and fissures was later on MR imaging than described in past anatomical and embryological studies. In addition, the sudden decrease in height of the fourth ventricle and the cerebral aqueduct found in our study might reflect the presence of communication between the fourth ventricle and subarachnoid space.

Prenatal aqueductal stenosis as a cause of congenital hydrocephalus in the inbred rat LEW/Jms.

We studied the microscopic morphological changes in congenital hydrocephalus in the inbred rat, LEW/Jms, on gestational days 17, 18, and 20 and during the neonatal period to clarify the etiopathogenesis, focusing particularly on the aqueductal changes. At 1 day of age, ventriculomegaly was limited to the lateral and III ventricles, and the aqueduct was obstructed, with the appearance of simple stenosis. On gestational days 20 and 18, the hydrocephalic rats showed occluded aqueducts, which paralleled the finding of hydrocephalus in the newborn rats. On gestational day 17, all eight models examined showed the same size ventricles. However, an aqueductal obstruction was observed in one of them. The other seven rats showed the aqueduct patent. From these observations, it can be concluded that the rat shows an aqueductal obstruction on gestational day 17 and appears to develop hydrocephalus with age. The aqueductal obstruction was considered to be the primary change and not a secondary phenomenon. The site of obstruction was the anterior part of the aqueduct (level of anterior colliculus) at every stage. Aqueductal obstruction following the developmental anomaly of the midbrain in the embryonic stage might thus be the primary cause of congenital hydrocephalus in rats LEW/Jms.

Dopaminergic cells align along radial glia in the developing mesencephalon of the rat.

Studies were performed to examine the relation of dopaminergic cells and radial glia in the developing mesencephalon of the rat at ages E12-E20. Dopaminergic cells were immunolabelled with an antiserum which recognizes tyrosine hydroxylase, and radial glia were immunolabelled with a monoclonal antibody which recognizes vimentin. The vimentin-immunoreactive fibres of radial glia were noted at E12. At E12, and more clearly at later time points, the radial glia extended from the aqueduct to the pial surface, and this pattern persisted throughout the prenatal period. Tyrosine hydroxylase-immunoreactive cells were located along the ventral surface of the mesencephalon at age E13. At age E15, E16, and E18 the tyrosine hydroxylase-immunoreactive cells were present from the aqueduct to the ventral pial surface of the mesencephalon and were aligned along radial glia. Our study suggests that radial glia provide paths for migration of dopaminergic cells in the mantle layer from E15 to E18 of the developing mesencephalon. It also suggests that some dopaminergic cells between E15 and E18 may express tyrosine hydroxylase during their migration through the mantle layer and prior to reaching the location they occupy in the adult brain.

Facial and neuroepithelial abnormalities in a neurological mutant with congenital hydrocephalus. A scanning electron microscope study.

This investigation was carried out to determine the early structural abnormalities of the cephalic region in a genetic mutant of the rat characterized by prenatal aqueductal stenosis and hydrocephalus. The appearance of hydrocephalic and control embryos was examined on days 13-15 of gestation, and the structure and organization of the neuroepithelium and basal lamina were studied using scanning electron microscopy. In addition to some overall developmental delay, hydrocephalic embryos were characterized by abnormalities of forebrain and midbrain development, and eye and external ear anomalies. There were also associated defects of the midfacial region. The lateral cell surface of the neuroepithelium reflected the developmental delay of hydrocephalic embryos, and failed to undergo the morphogenetic cell-shaping changes seen in control embryos. There were also variations in the number of lateral cell-cell specializations as well as regions of neuroepithelial disorganization and occasional herniation into the mesenchymal compartment. The role of the neuroepithelial basal lamina and extracellular matrix in the development of these defects is considered.

Congenital hydrocephalus following X-irradiation of pregnant rats on an early gestational day.

When pregnant rats were X-irradiated at a dose of 100 R on gestational day 9.5, a considerable number of postnatally-viable hydrocephalic offspring resulted, all of which were accompanied with bilateral micro- or anophthalmia. Histological studies revealed that the cerebral aqueduct of the congenital hydrocephalic brain was severely stenosed, and the subcommissural organ was reduced in size and displaced at some distance from the anterior end of the cerebral aqueduct. From embryological studies, it was considered that the maldevelopment of the subcommissural organ in the X-irradiated fetus might cause a reduction in the amount of its secretions which function as a cushion preventing complete closure of the cerebral aqueduct during fetal life, resulting in stenosis of the cerebral aqueduct.

Gliogenesis and ependymogenesis during embryonic development of the rat. An autoradiographic study.

With the aid of [3H]thymidine autoradiography gliogenesis and ependymogenesis were studied in the brain of the rat during embryonic development. Gliogenesis was found to begin on day 17 of gestation in the caudal regions of the brain stem, and to spread rostrally. On days 20 and 21 of gestation gliogenesis reached a peak, and then declined. Ependymogenesis began earlier and showed the following pattern: day 14 of gestation in the 4th ventricle and cerebral aqueduct, day 15 in the 3rd ventricle, and day 17 in the lateral ventricles reaching a peak on different days in different sites. Both gliogenesis and ependymogensis continued up to the last day of gestation, day 22. Issues pertaining to gliogenesis and the formation of glioblasts, and the relationship between gliogenesis and ependymogenesis are discussed.