Position of the choroid plexus of the fourth ventricle in first- and second-trimester fetuses: a novel approach to early diagnosis of cystic posterior fossa anomalies

'Choroid bar': easy-to-seek marker of normal posterior fossa at 12-14 weeks' gestation

OBJECTIVES

Our objectives were: (1) to assess the visualization rate of the choroid bar in a consecutive series of 306 first-trimester scans; (2) to verify, in this cohort of fetuses, the normality of the posterior fossa later in pregnancy; and (3) to confirm the non-visualization of the choroid bar in a retrospective series of fetuses with posterior fossa malformations.

METHODS

This study included a prospective and a retrospective series. The former comprised 306 fetuses undergoing routine obstetric ultrasound at our unit in both the first and second trimesters over a 6-month period, while the latter comprised 12 cases of posterior fossa malformations. In the prospective study, the presence of the choroid bar, which is defined as a visually continuous, homogeneously hyperechogenic, thick structure bridging the cisterna magna from side to side, was evaluated at the end of the first-trimester nuchal translucency scan. In the retrospective study, previously acquired three-dimensional volume datasets were processed in order to assess whether the choroid bar could be visualized in cases of open spinal dysraphisms and vermian cystic anomalies. In the prospective study, confirmation of a normal posterior fossa was based on the sonographic features of this anatomical region at the time of the second-trimester anomaly scan at 19-21 weeks' gestation, while, in the retrospective study, it was based on autopsy results, when available, or further direct imaging of the defect later in pregnancy.

RESULTS

In the prospective study, the choroid bar could be visualized in all 306 fetuses, on transabdominal ultrasound in 287 (93.8%) cases and on transvaginal ultrasound in 19 (6.2%) cases. The choroid bar was displayed with a ventral/dorsal approach in 67 (21.9%) cases, with a lateral approach in 56 (18.3%) cases and with both in 183 (59.8%) cases. All 306 cases were confirmed to have a sonographically normal posterior fossa at 19-21 weeks. On the other hand, in the retrospective study, it was not possible to visualize the choroid bar in any of the fetuses with posterior fossa malformations.

CONCLUSIONS

We have described a new sign, the choroid bar, consistent with a normal posterior fossa at 12-14 weeks' gestation. The choroid bar provides the option of screening for major abnormalities of the posterior fossa, since its absence raises suspicion of both open spinal dysraphisms and posterior fossa cystic malformations. At the same time, it is easy to visualize, as it can be seen with all lines of insonation. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

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.

ChOP-CT: quantitative morphometrical analysis of the Hindbrain Choroid Plexus by X-ray micro-computed tomography

The Hindbrain Choroid Plexus is a complex, cerebrospinal fluid-secreting tissue that projects into the 4th vertebrate brain ventricle. Despite its irreplaceability in the development and homeostasis of the entire central nervous system, the research of Hindbrain Choroid Plexus and other Choroid Plexuses has been neglected by neuroscientists for decades. One of the obstacles is the lack of tools that describe the complex shape of the Hindbrain Choroid Plexus in the context of brain ventricles. Here we introduce an effective tool, termed ChOP-CT, for the noninvasive, X-ray micro-computed tomography-based, three-dimensional visualization and subsequent quantitative spatial morphological analysis of developing mouse Hindbrain Choroid Plexus. ChOP-CT can reliably quantify Hindbrain Choroid Plexus volume, surface area, length, outgrowth angle, the proportion of the ventricular space occupied, asymmetries and general shape alterations in mouse embryos from embryonic day 13.5 onwards. We provide evidence that ChOP-CT is suitable for the unbiased evaluation and detection of the Hindbrain Choroid Plexus alterations within various mutant embryos. We believe, that thanks to its versatility, quantitative nature and the possibility of automation, ChOP-CT will facilitate the analysis of the Hindbrain Choroid Plexus in the mouse models. This will ultimately accelerate the screening of the candidate genes and mechanisms involved in the onset of various Hindbrain Choroid Plexus-related diseases.

Impact of choroid plexus size in prenatal diagnosis of normal and abnormal closure of fourth ventricle

OBJECTIVE

To assess the role of the choroid plexus (CP) of the fourth ventricle (4V) in fetuses with an open 4V and a normal cerebellar vermis.

METHODS

Two groups of patients were recruited in two fetal medicine referral centers. The prospectively collected control group included singleton pregnancies with a normal sonographic examination after first-trimester combined screening for chromosomal abnormalities and normal outcome, recruited in the period between 2019 and 2022. The study group was selected retrospectively by searching our databases to identify all cases with an isolated open 4V and normal anatomy and size of the cerebellar vermis. The inclusion criteria of the study group were: (1) gestational age between 20 and 22 weeks; (2) a brainstem-vermis angle ≥ 18° in the midsagittal plane with an otherwise normal cerebellum and vermis; (3) 4V-CP visible and seen separately from the vermis; (4) absence of other intra- and extracranial anomalies; and (5) available prenatal and/or postnatal magnetic resonance imaging (MRI) data.

RESULTS

In 169 cases of the control group, the 4V-CP was seen separately from the cerebellar vermis and was noticed to progressively fill the space caudal to the 4V, between the vermis and brainstem. From 12 to 22 weeks, the surface areas of the vermis and medial portion of the 4V-CP increased progressively with advancing gestation (P < 0.0001). Intra- and interobserver correlation analysis showed good reproducibility for the measurements. Among the cases with an open 4V and a normal vermis, it was retrospectively feasible to visualize the 4V-CP separately from the inferior part of the vermis in 41 fetuses. In five of these cases, the open 4V was due to a small CP. In all 41 fetuses, the diagnosis on MRI was isolated upward rotation of the cerebellar vermis, and no additional anomaly was found.

CONCLUSIONS

Closure of the 4V is dependent on the 4V-CP and not only the cerebellar vermis. In fact, a small CP may represent another cause of an open 4V. Therefore, separate visualization of the 4V-CP and cerebellar vermis is crucial to improve discrimination between the different causes of an open 4V at the anomaly scan and its clinical implications. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

How to differentiate PHACES syndrome from Blake's pouch cyst in first half of pregnancy

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The role of routine first-trimester ultrasound screening for central nervous system abnormalities: a longitudinal single-center study using an unselected cohort with 3-year experience

BACKGROUND

To evaluate the role of a standardized first-trimester scan in screening different kinds of central nervous system malformations and to report a 3-year experience from a tertiary center using an unselected cohort.

METHODS

This was a retrospective analysis of prospectively collected data from a single center evaluating first-trimester scans with predesigned standardized protocols performed between 1 May 2017 and 1 May 2020, involving 39,526 pregnancies. All pregnant women underwent a series of prenatal ultrasound scans at 11-14, 20-24, 28-34 and 34-38 weeks of gestation. Abnormalities were confirmed by magnetic resonance imaging, postmortem examination or trained ultrasound professionals. Pregnancy outcomes and some postnatal follow-up were obtained from maternity medical records and telephone calls.

RESULTS

A total of 38,586 pregnancies included in the study. The detection rates of CNS anomalies by ultrasound in the first, second, third and late third trimester were 32%, 22%, 25%, and 16%, respectively. And there were 5% of CNS anomalies missed by prenatal ultrasound. In the first-trimester scan, we diagnosed all cases of exencephaly, anencephaly, alobar holoprosencephaly and meningoencephalocele, and some cases of posterior cranial fossa anomalies (20%), open spina bifida (67%), semilobar holoprosencephaly (75%) and severe ventriculomegaly (8%). Vein of Galen aneurysmal malformation, closed spina bifida, lobar holoprosencephaly, intracranial infection, arachnoid cyst, agenesis of the corpus callosum, cysts of the septum pellucidum and isolated absence of the septum pellucidum were never detected during the first trimester. The abortion rates of fetal CNS anomalies detected by first-trimester scan, second-trimester scan, and third- trimester scan were 96%, 84% and 14%, respectively.

CONCLUSIONS

The study showed that almost 1/3 of central nervous system anomalies were detected by the standard first-trimester scan and these cases were associated with a high rate of abortion. Early screening for fetal abnormalities gives parents more time for medical advice and safer abortion if needed. It is therefore recommended that some major CNS anomalies should be screened in the first trimester. The standardized anatomical protocol, consisting of four fetal brain planes, were recommended for routine first trimester ultrasound screening.

A myriad of posterior fossa cysts: A single center experience

Antenatal posterior fossa cystic lesions are intimidating due to overlapping imaging features of benign and severe malformations. Sonographic assessment of the posterior fossa with good resolution median sagittal and axial views, either primary or secondarily reconstructed, plays the lead role in antenatal evaluation, further enhanced when sequential assessments are added. We present 10 cases of fetal posterior fossa cystic lesions diagnosed in the first and second trimesters that were sequentially analyzed and followed up till delivery or termination. The ultrasound imaging appearance, evolution, and morphometry have been presented in this article.

Qualitative and quantitative study of fetal posterior fossa during the first trimester in a Chinese population

Background

To establish the normal reference ranges for parameters related to the fetal posterior fossa in the first trimester (11 ~ 13+6 weeks of gestation) and to analyze the relationship between them and crown-rump length (CRL) among the Chinese population.

Methods

Singleton pregnancies of 11 ~ 13⁺⁶ weeks (CRL:45 ~ 84 mm) with both parents from China were randomly selected from January 2021 to November 2021. The related parameters of the posterior fossa including cisterna magna (CM), intracranial translucency (IT), brain stem (BS), brain stem to the occipital bone (BSOB), and brain stem/brain stem to occipital bone (BS/BSOB) were evaluated and measured in nuchal translucency (NT) mid-sagittal section clearly by an experienced sonographer (operator 1). To assess the reproducibility of the measurements, we randomly selected 50 pregnant women. According to the blind method, operators 1 and 2 respectively screened and measured relevant parameters. In addition, operator 1 examined and measured relevant parameters again 2 h after the first.

Results

This study included 1663 fetuses. All fetuses can clearly show the three spaces of the fetal posterior fossa. The ICCs (95% CI) of intra-operator reproducibility of CM, IT, BS, BSOB, BS/BSOB were 0.981 (0.952 ~ 0.991, P < 0.001), 0.929 (0.866 ~ 0.961, P < 0.001), 0.970 (0.946 ~ 0.983, P < 0.001), 0.991 (0.974 ~ 0.996, P < 0.001), 0.939 (0.892 ~ 0.965, P < 0.001), respectively; The ICCs (95% CI) of inter-operator reproducibility 0.926 (0.860 ~ 0.960, P < 0.001), 0.810 (-0.083 ~ 0.940, P < 0.001), 0.820 (0.645 ~ 0.904, P < 0.001), 0.804 (0.656 ~ 0.888, P < 0.001), 0.772 (0.599 ~ 0.871, P < 0.001), respectively. There was a linear correlation between CRL and the parameters related to the posterior fossa (CM, IT, BS, BSOB, BS/BSOB). CM (mm) = -1.698 + 0.532 × CRL (cm) (r = 0.829, P < 0.001); IT (mm) = 0.701 + 0.179 × CRL (cm) (r = 0.548, P < 0.001); BS (mm) = 0.403 + 0.349 × CRL (cm) (r = 0.716, P < 0.001); BSOB (mm) = -0.277 + 0.719 × CRL (cm) (r = 0.829, P < 0.001); BS/BSOB = 0.747—0.021 × CRL (cm) (r = 0.196, P < 0.001).

Conclusions

Qualitative and quantitative assessment of the fetal posterior fossa structure was feasible in the first trimester. We constructed the normal reference ranges of CM, IT, BS, BSOB, and BS/BSOB. Furthermore, CM, IT, BS, and BSOB were positively correlated with CRL, but BS/BSOB was negatively correlated with CRL.

First trimester examination of fetal anatomy: clinical practice guideline by the World Association of Perinatal Medicine (WAPM) and the Perinatal Medicine Foundation (PMF)

This recommendation document follows the mission of the World Association of Perinatal Medicine in collaboration with the Perinatal Medicine Foundation. We aim to bring together groups and individuals throughout the world for precise standardization to implement the ultrasound evaluation of the fetus in the first trimester of pregnancy and improve the early detection of anomalies and the clinical management of the pregnancy. The aim is to present a document that includes statements and recommendations on the standard evaluation of the fetal anatomy in the first trimester, based on quality evidence in the peer-reviewed literature as well as the experience of perinatal experts around the world.

Regulation of choroid plexus development and its functions

The choroid plexus (ChP) is an extensively vascularized tissue that protrudes into the brain ventricular system of all vertebrates. This highly specialized structure, consisting of the polarized epithelial sheet and underlying stroma, serves a spectrum of functions within the central nervous system (CNS), most notably the production of cerebrospinal fluid (CSF). The epithelial cells of the ChP have the competence to tightly modulate the biomolecule composition of CSF, which acts as a milieu functionally connecting ChP with other brain structures. This review aims to eloquently summarize the current knowledge about the development of ChP. We describe the mechanisms that control its early specification from roof plate followed by the formation of proliferative regions-cortical hem and rhombic lips-feeding later development of ChP. Next, we summarized the current knowledge on the maturation of ChP and mechanisms that control its morphological and cellular diversity. Furthermore, we attempted to review the currently available battery of molecular markers and mouse strains available for the research of ChP, and identified some technological shortcomings that must be overcome to accelerate the ChP research field. Overall, the central principle of this review is to highlight ChP as an intriguing and surprisingly poorly known structure that is vital for the development and function of the whole CNS. We believe that our summary will increase the interest in further studies of ChP that aim to describe the molecular and cellular principles guiding the development and function of this tissue.

Early second-trimester three-dimensional transvaginal neurosonography of fetal midbrain and hindbrain: normative data and technical aspects

OBJECTIVES

To provide a detailed description of the sonographic appearance and development of various fetal structures of the midbrain and hindbrain (MBHB) during the early second trimester, and to evaluate the impact of the frequency of the transvaginal sonography (TVS) transducer on the early recognition of these structures.

METHODS

This was a retrospective analysis of three-dimensional volumetric datasets of the MBHB from apparently normal fetuses at 14-19 gestational weeks, acquired by TVS in the midsagittal view through the posterior fontanelle. Using a multiplanar approach, we measured the tectal thickness and length, aqueductal thickness, tegmental thickness and width and height of the Blake's pouch (BP) neck. In addition, we assessed the existence of early vermian fissures, the linear shape of the brainstem and the components of the fastigium. The correlation between gestational age according to last menstrual period and sonographic measurements of MBHB structures was evaluated using Pearson's correlation (r). A subanalysis was performed to assess the performance of a 5-9-MHz vs a 6-12-MHz TVS transducer in visualizing the MBHB structures in the early second trimester.

RESULTS

Sixty brain volumes were included in the study, obtained at a mean gestational age of 16.2 weeks (range, 14.1-19.0 weeks), with a transverse cerebellar diameter range of 13.0-19.8 mm. We found a strong correlation between gestational age and all MBHB measurements, with the exception of the tectal, tegmental and aqueductal thicknesses, for which the correlation was moderate. There was good-to-excellent intraobserver and moderate-to-good interobserver correlation for most MBHB measurements. We observed that the BP neck was patent in all fetuses between 14 and 18 weeks with decreasing diameter, and that the aqueductal thickness was significantly smaller at ≥ 18 weeks compared with at < 16 weeks. The early vermian fissures and the linear shape of the brainstem were present in all fetuses from 14 weeks. We found that, in the early second trimester, the horizontal arm of the presumed 'fastigium' evolves from the fourth ventricular choroid plexus and not the posterior vermis, indicating that this is not the fastigium. Standard- and high-resolution TVS transducers performed similarly in the assessment of MBHB anatomy.

CONCLUSION

Detailed early second-trimester assessment of the MBHB is feasible by transvaginal neurosonography and provides reference data which may help in the early detection of brain pathology involving the MBHB. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Low torcular Herophili position and large brainstem-tentorium angle in fetuses with open spinal dysraphism at 11-13 weeks' gestation

OBJECTIVE

To evaluate whether in fetuses with open spina bifida (OSB) the tentorium can be seen to be displaced downwards and vertically oriented by the time of the 11-13-week scan and whether this is reflected in an alteration of the brainstem-tentorium (BST) angle.

METHODS

The study population was recruited between 2015 and 2020 from three fetal medicine referral centers and comprised a control group and a study group of pregnancies with OSB. The control group was recruited prospectively and included singleton pregnancies with a normal sonographic examination after first-trimester combined screening for chromosomal abnormalities and normal outcome. The study group was selected retrospectively and included all cases with OSB between 2015 and 2020. All cases underwent detailed ultrasound assessment at 11 + 0 to 13 + 6 weeks' gestation. The position of the torcular Herophili (TH) was identified in the midsagittal view of the fetal brain with the use of color Doppler and was considered as a proxy for the insertion of the tentorium on the fetal skull. The BST angle was calculated in the same view and was compared between the two groups.

RESULTS

Sixty normal fetuses were included in the control group and 22 fetuses with OSB in the study group. In both groups, the BST angle was found to be independent of gestational age or crown-rump length (P = 0.8815, R²  = 0.0003861 in the controls, and P = 0.2665, R²  = 0.00978 in the OSB group). The mean BST angle was 48.7 ± 7.8° in controls and 88.1 ± 1.18°, i.e. close to 90°, in fetuses with OSB. Comparison of BST-angle measurements between the control group and cases with OSB showed a statistically significant difference (P = 0.0153). In all fetuses with OSB, the downward displacement of the TH and tentorium was clearly visible at the 11-13-week scan.

CONCLUSIONS

In fetuses with OSB, the BST angle is significantly larger than in normal controls, with the tentorium being almost perpendicular to the brainstem. This sign confirms the inferior displacement of the tentorium cerebelli with respect to its normal insertion on the occipital clivus as early as the first trimester of pregnancy and is useful in the diagnosis of Chiari-II malformation at this early stage. In fetuses with OSB, the low position of the tentorium and TH is clearly visible, even subjectively, at the 11-13-week scan. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.