From cavum septi pellucidi to anterior complex: how to improve detection of midline cerebral abnormalities

Neurosonographic Measurements of the Fetal Anterior Complex in Singleton Pregnancies

OBJECTIVE

To construct reference ranges of the fetal cerebral anterior complex, including ventricular index (VI), anterior horn of lateral ventricle width (AW), and cavum septi pellucidi (CSP) width, as a function of gestational age (GA), in Thai fetuses.

METHODS

Low-risk pregnancies were recruited to measure fetal anterior complex on axial transventricular and coronal transcaudate planes using transabdominal ultrasound. The downside and upside hemisphere were defined as cerebral hemisphere located distal and proximal to the transducer, respectively. The five variables, downside/upside VI, downside/upside AW and CSP width, were measured from each fetus. Best-fit models in predicting mean and standard deviation for each value as a function of GA were constructed, using regression analysis. Distributions of Z-scores of all values based on GA were created to evaluate the fitness of models. Intraclass correlation coefficients were used to assess inter-/intraobserver variability.

RESULTS

A total of 395 fetuses were measured for anterior complex. All parameters changed with GA with quadratic function. The models for predicting means and standard deviation of the five parameters as well as percentile charts were created. All models were proven well-fitted. The intra-/interobserver reliability coefficients of all values showed excellent agreement.

CONCLUSION

The reference ranges of the fetal anterior complex, including VI, AW, and CSP, in axial transventricular and coronal transcaudate planes have been established and available for clinical use.

Obliterated cavum septi pellucidi: is it always a benign finding? A case report and narrative review of the literature

OBJECTIVE

The septum pellucidum is a virtual cavity located at the anterior part of the brain midline, which only in fetal life has a certain amount of fluid inside. The presence of an obliterated cavum septi pellucidi (oCSP) in the prenatal period is poorly described in the literature but, nevertheless, it constitutes an important clinical dilemma for the fetal medicine specialist in terms of significance and prognosis. Moreover, its occurrence is increasing maybe because of the widespread of high-resolution ultrasound machine. The aim of this work is to review the available literature regarding the oCSP along with the description of a case-report of oCSP with an unexpected outcome.

METHODS

A search of the literature through Pubmed was performed up to December 2022 with the aim to identify all cases of oCSP previously described, using as keywords "cavum septi pellucidi," "abnormal cavum septi pellucidi," "fetus," and "septum pellucidum." Along with the narrative review, we describe a case-report of oCSP.

RESULTS

A 39 years old woman was diagnosed with a nuchal translucency between the 95° and 99° centile in the first trimester and an oCSP and "hookshaped" gallbladder at 20 weeks. Left polymicrogyria was found at fetal magnetic resonance imaging (MRI). Standard karyotype and chromosomal microarray analysis (CMA) were normal. After birth, the newborn presented signs of severe acidosis, untreatable seizures and multiorgan failure leading to death. A targeted gene analysis of the epilepsy panel revealed the presence of a de novo pathogenic variant involving the PTEN gene. The literature review identified four articles reporting on the oCSP of which three were case report and one was a case-series. The reported rate of associated cerebral findings is around 20% and the rate of adverse neurological outcome is around 6%, which is higher than the background risk of the general population.

CONCLUSIONS

This case-report and review of the literature shows that oCSP is a clinical entity poorly described so far and that, despite the generally good prognosis, it requires caution in counseling. The diagnostic work-up should include neurosonography while fetal MRI may be always indicated for non-isolated cases only, depending on local facilities. Targeted gene analysis or whole exome sequencing may be indicated for non-isolated cases.

Comparison of Cavum Septum Pellucidum Size in Euploid and Aneuploid Fetuses

OBJECTIVE

 The aim of the present study is to compare the cavum septum pellucidi (CSP) z-score in euploid and aneuploid fetuses and to investigate the performance of the CSP width/length and CSP width/biparietal diameter (BPD) ratios as a diagnostic marker in aneuploidy.

METHODS

 A total of 54 patients, 20 aneuploid and 35 euploid fetuses, between 18 and 37 weeks of gestation, were included in this retrospective study. The CSP width z-score was compared between the two groups. Receiver operating characteristic (ROC) curves were calculated for the CSP width/length and CSP width/BPD ratios to predict aneuploidy.

RESULTS

 The median CSP width was 4.8 mm (range, 1.8 to 8.5 mm) in the euploid group, and 5.4 mm (range 3.1 to 8.4 mm) in the aneuploid group. Cavum septum pellucidi width z-score, CSP width/length ratio, and CSP width/BPD ratio were significantly higher in fetuses with aneuploidy than in fetuses with normal karyotype (p = 0.001; p = 0.013; p = 0.028). In the ROC analysis, the CSP width/length ratio had the optimal cutoff value of 0.59, with 72.0% sensitivity and 58.0% specificity, and for the CSP width/BPD ratio, the cutoff value was 0.081 with 83.0% sensitivity and 61.0% specificity for detection of aneuploidy.

CONCLUSION

 CSP width z-score was found to be increased in aneuploid fetuses. The CSP width /BPD ratio can be used as a new marker for predicting aneuploidy.

Obliterated cavum septi pellucidi: Clinical significance and role of fetal magnetic resonance

INTRODUCTION

The objective of this study was to describe a cohort of fetuses with an ultrasound prenatal diagnosis of obliterated cavum septi pellucidi (oCSP) with the aim to explore the rate of associated malformations, the progression during pregnancy and the role of fetal magnetic resonance imaging (MRI).

MATERIAL AND METHODS

This was a retrospective multicenter international study of fetuses diagnosed with oCSP in the second trimester with available fetal MRI and subsequent ultrasound and/or fetal MRI follow-up in the third trimester. Where available, postnatal data were collected to obtain information on neurodevelopment.

RESULTS

We identified 45 fetuses with oCSP at 20.5 weeks (interquartile range 20.1-21.1). oCSP was apparently isolated at ultrasound in 89% (40/45) and fetal MRI found additional findings in 5% (2/40) of cases, including polymicrogyria and microencephaly. In the remaining 38 fetuses, fetal MRI found a variable amount of fluid in CSP in 74% (28/38) and no fluid in 26% (10/38). Ultrasound follow-up at or after 30 weeks confirmed the diagnosis of oCSP in 32% (12/38) while fluid was visible in 68% (26/38). At follow-up MRI, performed in eight pregnancies, there were periventricular cysts and delayed sulcation with persistent oCSP in one case. Among the remaining cases with normal follow-up ultrasound and fetal MRI findings, the postnatal outcome was normal in 89% of cases (33/37) and abnormal in 11% (4/37): two with isolated speech delay, and two with neurodevelopmental delay secondary to postnatal diagnosis of Noonan syndrome at 5 years in one case and microcephaly with delayed cortical maturation at 5 months in the other.

CONCLUSIONS

Apparently isolated oCSP at mid-pregnancy is a transient finding with the visualization of the fluid later in pregnancy in up to 70% of cases. At referral, associated defects can be found in around 11% of cases at ultrasound and 8% at fetal MRI indicating the need for a detailed evaluation by expert physicians when oCSP is suspected.

Role of Fetal Magnetic Resonance Imaging in Differentiating Isolated Septal Agenesis from Septo-Optic Dysplasia: Case Study and Review

INTRODUCTION

The detection of absent septi pellucidi (ASP) during obstetric ultrasound is a rare event. However, the clinical implications of this finding are significant. ASP can be associated with severe central nervous system anomalies such as holoprosencephaly, agenesis/dysgenesis of the corpus callosum, schizencephaly, severe ventriculomegaly, and open neural tube defects. In such cases, the prognosis is poor. When no such anomalies are identified, isolated ASP usually carries a good prognosis. However, some fetuses thought to have isolated ASP actually have septo-optic dysplasia (SOD), which is associated with optic nerve hypoplasia, hypothalamic-pituitary dysfunction, and developmental delay.

CASE PRESENTATION

A case in which fetal 3.0 Tesla magnetic resonance imaging (MRI) was considered crucial to definitively diagnose isolated ASP is presented. A review of the literature was conducted and analyzed to determine the role of MRI in the evaluation of fetuses with ASP, with special consideration on the differential diagnosis between isolated ASP and SOD.

CONCLUSION

Differentiating isolated ASP from SOD is imperative for adequate prenatal counseling. Unfortunately, making a prenatal diagnosis of SOD requires visualization and evaluation of the fetal optic nerves, chiasm, and pituitary gland, which is very demanding and not always possible using ultrasound. Fetal MRI has the potential of obtaining high-quality images of the fetal brain, and therefore this technique can be used for establishing the differential diagnosis in utero.

Prenatal diagnosis of Aicardi syndrome based on a suggestive imaging pattern: A multicenter case-series

Objectives

To characterize a suggestive prenatal imaging pattern of Aicardi syndrome using ultrasound and MR imaging.

Methods

Based on a retrospective international series of Aicardi syndrome cases from tertiary centers encountered over a 20‐year period (2000–2020), we investigated the frequencies of the imaging features in order to characterize an imaging pattern highly suggestive of the diagnosis.

Results

Among 20 cases included, arachnoid cysts associated with a distortion of the interhemispheric fissure were constantly encountered associated with complete or partial agenesis of the corpus callosum (19/20, 95%). This triad in the presence of other CNS disorganization, such as polymicrogyria (16/17, 94%), heterotopias (15/17, 88%), ventriculomegaly (14/20, 70%), cerebral asymmetry [14/20, 70%]) and less frequently extra‐CNS anomaly (ocular anomalies [7/11, 64%], costal/vertebral segmentation defect [4/20, 20%]) represent a highly suggestive pattern of Aicardi syndrome in a female patient.

Conclusion

Despite absence of genetic test to confirm prenatal diagnosis of AS, this combination of CNS and extra‐CNS fetal findings allows delineation of a characteristic imaging pattern of AS, especially when facing dysgenesis of the corpus callosum.

What is already known about this topic?

Aicardi syndrome (AS) is a rare developmental encephalopathy, characterized by the classic triad of infantile spasms, agenesis of the corpus callosum, and chorioretinal lacunae

As the genetic etiology of AS is unknown and its classic triad cannot be extrapolated to prenatal diagnosis, to establish a prenatal imaging pattern is of major interest

What does this study add?

We confirmed and completed a prenatal imaging pattern highly suggestive of AS, based on the most frequent features encountered in a large series: arachnoid cysts associated with a distortion of the interhemispheric fissure, agenesis of the corpus callosum, cortical malformations and heterotopias, and less frequently extra‐CNS anomaly (ocular anomalies, costal/vertebral segmentation defect)

Ultrasound and Magnetic Resonance Imaging of Agenesis of the Corpus Callosum in Fetuses: Frontal Horns and Cavum Septi Pellucidi Are Clues to Earlier Diagnosis

OBJECTIVES

We hypothesized that: (1) fetal frontal horn (FH) morphology and their proximity to the cavum septi pellucidi (CSP) can assist in suspecting complete agenesis of the corpus callosum (cACC) and partial agenesis of the corpus callosum (pACC) earlier than known indirect ultrasound (US) findings; (2) FHs assist in differentiating a true CSP from a pseudocavum; and (3) magnetic resonance imaging (MRI) is useful in learning FH morphology and pseudocavum etiology.

METHODS

Thirty-two patients with cACC and 9 with pACC were identified on an Institutional Review Board-approved retrospective review. Of the 41 cases, 40 had prenatal US, and 21 had prenatal MRI; 17 had follow-up neonatal US, and 14 had follow-up neonatal MRI. Variables evaluated retrospectively were the presence of a CSP or a pseudocavum, ventricle size and shape, and FH shape (comma, trident, parallel, golf club, enlarged, or fused). Displacement between the inferior edge of the FH and the midline or cavum/pseudocavum was measured.

RESULTS

Fetal FHs had an abnormal shape in 77% ≤20 weeks' gestation, 86% ≤24 weeks, and 90% >24 weeks. Frontal horns were laterally displaced greater than 2 mm in 85% ≤20 weeks, 91% ≤24 weeks, and 95% >24 weeks. The CSP was absent in 100% of cACC cases and 78% of pACC cases, and a pseudocavum was present in 88% of cACC cases and 78% of pACC cases across gestation. Magnetic resonance imaging confirmed US pseudocavums to be focal interhemispheric fluid or an elevated/dilated third ventricle.

CONCLUSIONS

Frontal horns assist in assessing ACC ≤24 weeks and throughout gestation. Pseudocavums, often simulating CSPs, are common in ACC. Frontal horn lateral displacement and abnormal morphology, recognized by MRI correlations, are helpful in differentiating a pseudocavum from a true CSP. A normal CSP should not be cleared on screening US unless normally shaped FHs are seen directly adjacent to it.

Feasibility and agreement of including anterior-posterior complexes and landmarks of the proximal hemisphere into basic examination of the fetal brain: A prospective study

OBJECTIVE

To assess the feasibility of identifying structures included in anterior complex (AC) and posterior complex (PC), as well as a series of anatomic landmarks that could help to demonstrate the integrity of the cerebral proximal hemisphere (PH).

METHODS

This was a prospective observational multicenter study of healthy pregnant women attending routine ultrasound screening at 20 + 0 to 33 + 6 weeks' gestation. Six physicians performed transabdominal (TA) ultrasound, in order to obtain the planes required to visualize the AC, PC, and PH. Blind analysis by a nonexpert and two experts in fetal neurosonography was used to assess the structures included in each plane view.

RESULTS

In the population studied (n = 747), detection of the structure rates for AC, PC, and proximal hemisphere was of 94%, 93%, and 96%, respectively, with an agreement of 97%, 94%, and 98% when comparing an expert and a nonexpert in fetal brain examiner. Detection of structures in the proximal hemisphere was significantly higher when observed through the proximal hemisphere plane rather than the transventricular plane.

CONCLUSION

Our results suggest that inclusion of AC and PC complexes visualization, as well as real-time access to the proximal hemisphere, is feasible and could improve the prenatal detection of fetal cerebral anomalies.

Antenatal diagnosis of absence of septum pellucidum

The absence of septum pellucidum (ASP) is a rare disease, which affects the structure of the brain. It is either isolated or associated with various congenital brain malformations. The diagnosis of ASP can be performed by second-trimester ultrasound. When the ASP is isolated, prenatal counseling is optimistic regarding neurological outcome, but there is a 20% risk of septo-optic dysplasia in the neonate.

New Insights into the Anterior Complex

OBJECTIVE

To introduce visualization of the germinal matrix (GM), external angle of the frontal horn, and periventricular white matter while evaluating the anterior complex (AC) during basic ultrasound assessment of the fetal brain.

CASE PRESENTATIONS

This is a retrospective observational study of healthy women with singleton pregnancies, with no increased risk of fetal central nervous system anomalies, attending routine ultrasound screening at 20-32 weeks' gestation. Seventeen cases are presented in which an abnormal aspect of the GM or external angle of the frontal horn or periventricular white matter on AC evaluation has allowed a prenatal diagnosis of peri-intraventricular hemorrhage, subependymal cysts, connatal cysts, periventricular venous hemorrhagic infarction, and white matter injury.

CONCLUSION

An extended AC evaluation could significantly improve the -diagnosis of hemorrhagic/cystic/hypoxic-ischemic lesions during the performance of a basic ultrasound study of the fetal brain.

Ultrasound Measurements of Frontal Horns and the Cavum Septi Pellucidi in Healthy Fetuses in the Second and Third Trimesters of Pregnancy

OBJECTIVES

To assess the visualization rate and size of the frontal horns (FHs) and cavum septi pellucidi (CSP) in healthy fetuses throughout pregnancy.

METHODS

After Institutional Review Board approval, 522 consecutive uncomplicated singleton pregnancies between 15 and 39 gestational weeks were enrolled in the study. Ultrasound measurements of the anterior horn width (AHW), center from the horn distance (CFHD), distance from the FHs to the CSP, and CSP width were retrospectively performed using axial transventricular or transcerebellar planes. Available maternal body mass indices were recorded.

RESULTS

At least 1 FH was seen in 78% of the cases. The mean AHW decreased over the second trimester and plateaued in the third trimester. The CFHD plateaued in the second trimester and increased in the third trimester. Downside FHs were generally larger than upside FHs. More FHs were measured in transventricular (69%) than transcerebellar (31%) planes. Frontal horns were seen with high, low, and no confidence in 57%, 21%, and 22% of cases, respectively. No-confidence rates were 17% in the second trimester and 42% in the third trimester. The CSP was not visualized in 4% of cases; 15 of 19 cases of a nonvisualized CSP were scanned between 18 and 37 weeks. Mean body mass indices ± SDs were 27.6 ± 6.7 kg/m² for the patients in cases of a visualized CSP and 32.4 ± 9.1 kg/m² for the patients in cases of a nonvisualized CSP.

CONCLUSIONS

Normative data for the fetal FH and CSP width were established. Frontal horns are more frequently seen on transventricular views and are difficult to confidently assess in the late third trimester. This study challenges previously reported data that the CSP is seen in 100% of cases from 18 to 37 weeks.