The aqueduct of Sylvius: a sonographic landmark for neural tube defects in the first trimester

Computational methods for the analysis of early-pregnancy brain ultrasonography: a systematic review

BACKGROUND

Early screening of the brain is becoming routine clinical practice. Currently, this screening is performed by manual measurements and visual analysis, which is time-consuming and prone to errors. Computational methods may support this screening. Hence, the aim of this systematic review is to gain insight into future research directions needed to bring automated early-pregnancy ultrasound analysis of the human brain to clinical practice.

METHODS

We searched PubMed (Medline ALL Ovid), EMBASE, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, and Google Scholar, from inception until June 2022. This study is registered in PROSPERO at CRD42020189888. Studies about computational methods for the analysis of human brain ultrasonography acquired before the 20th week of pregnancy were included. The key reported attributes were: level of automation, learning-based or not, the usage of clinical routine data depicting normal and abnormal brain development, public sharing of program source code and data, and analysis of the confounding factors.

FINDINGS

Our search identified 2575 studies, of which 55 were included. 76% used an automatic method, 62% a learning-based method, 45% used clinical routine data and in addition, for 13% the data depicted abnormal development. None of the studies shared publicly the program source code and only two studies shared the data. Finally, 35% did not analyse the influence of confounding factors.

INTERPRETATION

Our review showed an interest in automatic, learning-based methods. To bring these methods to clinical practice we recommend that studies: use routine clinical data depicting both normal and abnormal development, make their dataset and program source code publicly available, and be attentive to the influence of confounding factors. Introduction of automated computational methods for early-pregnancy brain ultrasonography will save valuable time during screening, and ultimately lead to better detection, treatment and prevention of neuro-developmental disorders.

FUNDING

The Erasmus MC Medical Research Advisor Committee (grant number: FB 379283).

Basic sonographic examination of the fetal brain at 11-13 weeks' gestation: Rationale for a simple and reliable four-step technique

The widespread incorporation of first-trimester scanning between 11 and 13 weeks' gestation has shifted from the screening of chromosomal abnormalities, mainly by measuring nuchal translucency thickness and visualization of the nasal bone, to a more detailed study of the fetal anatomy leading to early detection of several structural congenital anomalies. This goal can be improved by the routine and focused sonographic assessment of specific anatomic planes and the identification of distinctive landmarks that can help disclosing a particular, non-evident condition. In this article we present the basis for a basic, early examination of the fetal brain during screening using a four-step technique, which can be readily incorporated during the first-trimester scan. The technique includes the focused visualization of the cranial contour, choroid plexuses of the lateral ventricles and midline, aqueduct of Sylvius, brainstem, fourth ventricle, and the choroid plexus of the fourth ventricle. The rationale for this approach is presented and discussed.

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.

First-Trimester Cranial Ultrasound Markers of Open Spina Bifida

OBJECTIVES

To evaluate cranial ultrasound markers during a first-trimester routine ultrasound examination for screening for open spina bifida (OSB).

METHODS

Midsagittal and axial images of the fetal head obtained from fetuses with spina bifida and unaffected control fetuses at 11 weeks to 13 weeks 6 days were analyzed retrospectively. The observed markers of the posterior brain included the 4- versus 3-line view, the brain stem (BS)-to-brain stem-occipital bone (BSOB) distance ratio (BS/BSOB), the position relationship between the maxillo-occipital (MO) line and the midbrain-BS junction, and the crash sign status.

RESULTS

This study included 9 OSB cases, 2 closed spina bifida (CSB) cases, and 200 unaffected controls. Eight of 9 OSB cases had informative midsagittal views of the head. The 3-line view (abnormal) and BS/BSOB greater than 1 (abnormal) were observed in 87.5% (7 of 8) and 100% (8 of 8), respectively. The midbrain-BS junction was below or nearly on the MO line (abnormal) in 100% (8 of 8). Seven of the cases had informative axial views of the head. The crash sign (abnormal) was observed in 85.7% (6 of 7). A 3-line view was seen in all of the cases that had a positive crash sign. Neither of the 2 cases of CSB and none of the controls had any of the 4 first-trimester intracranial ultrasound markers of OSB.

CONCLUSIONS

The 4 first-trimester intracranial ultrasound markers investigated in this study appear to be very good markers of OSB, especially a BS/BSOB greater than 1 and an abnormal MO line. The crash sign and 3-line view were observed in the same fetus. In our study, these ultrasound findings were not helpful in CSB.

[Prenatal ultrasound prognostic of myelomeningocele at the era of fetal surgery]

Myelomeningocele (MMC) is a severe congenital condition responsible for motor and sensory impairments of the lower limbs, incontinence and cognitive impairment. Its screening, sometimes as early as the first trimester, is one of the major goals of modern prenatal care, supported by the emergence of prenatal surgery that results in a significant improvement in motor function, ambulation and ventriculoperitoneal shunt rate in patients undergoing in-utero surgery. From screening to pre- and post-operative prognostic evaluation, prenatal ultrasound is now an essential tool in the antenatal management of this condition. Using the multi planar and three-dimensional modes, it can be used to assess the vertebral level of MMC, which remains the key antenatal prognostic marker for motor function and ambulation, incontinence and the need for a ventriculo-peritoneal shunt. A careful and systematic ultrasound examination also makes it possible to assess the severity and progression of ventriculomegaly, to search for associated cerebral, spinal cord or vertebral anomalies, or to rule out exclusion criteria for in-utero surgery such as severe kyphosis or serious cortical anomalies. New tools from post-natal evaluation, such as the "metameric" ultrasound assessment of lower limb mobility, appear to be promising either for the initial examination or after in-utero surgery. Ultrasonography, associated with fetal MRI, cytogenetic and next generation sequencing, now allows a highly customized prognostic evaluation of these fetuses affected by MMC and provides the parents with the best possible information on the expected benefits and limitations of fetal surgery.

Diagnostic accuracy of fetal choroid plexus length to head biometry ratio at 11 to 13 weeks for open spina bifida

BACKGROUND

Open spina bifida is a major congenital anomaly with an estimated incidence of <1 in 1000. The diagnosis of open spina bifida is usually made during the second trimester, but first-trimester detection rate of spina bifida is increasingly reported. Recently, the mean choroid plexus length to occipitofrontal diameter ratio was reported to be increased in fetuses with open spina bifida. The ratio reflects the so-called dry brain effect caused by cerebrospinal fluid leakage and expansion of the choroid plexus into the lateral ventricles. The mean choroid plexus length to occipitofrontal diameter ratio appears to be a promising tool for early detection of open spina bifida, but its diagnostic accuracy is yet to be determined in a large cohort.

OBJECTIVE

This study aimed to assess the predictive accuracy of mean choroid plexus length to occipitofrontal diameter ratio recorded at 11 to 13 weeks' gestation for the detection of open spina bifida.

STUDY DESIGN

This was a retrospective cohort of patients treated in a tertiary referral center. Fetuses in which open spina bifida was detected at 16 to 24 weeks' gestation and normal fetuses were included in the cohort. Biparietal diameter and occipitofrontal diameter were measured in an axial view. The length of choroid plexus was measured along its longest diameter in the same plane. Ultrasound images were examined offline, and the operator was blinded to the clinical diagnosis. The predictive accuracy was evaluated using the area under the curve and positive and negative predictive values.

RESULTS

We included 3300 pregnant women, of whom 24 (0.73%) had the fetuses affected by open spina bifida. The area under the curve values were 0.921 for mean choroid plexus length to occipitofrontal diameter ratio and 0.933 for its multiple of the median. Mean choroid plexus length to biparietal diameter ratio indicated similar results, with area under the curve values of 0.928 and 0.931 for raw ratio and multiple of the median ratio models, respectively. The optimal cutoffs of the mean choroid plexus to occipitofrontal diameter ratio and multiple of the median ratios were 0.662 and 1.263, respectively. The optimal mean choroid plexus to occipitofrontal diameter ratio and multiple of the median ratio cutoffs provided a positive predictive value of 90.9% and a negative predictive value of 99.6%. The number of affected spinal segments was significantly higher in fetuses with a ratio above 0.662 (P=.022).

CONCLUSION

The mean choroid plexus length to occipitofrontal diameter ratio at 11 to 13 weeks' gestation is a promising tool for the prenatal detection of open spina bifida.

First-trimester fetal neurosonography: technique and diagnostic potential

Most brain abnormalities are present in the first trimester, but only a few are detected so early in gestation. According to current recommendations for first-trimester ultrasound, the fetal head structures that should be visualized are limited to the cranial bones, the midline falx and the choroid-plexus-filled ventricles. Using this basic approach, almost all cases of acrania, alobar holoprosencephaly and cephalocele are detected. However, the majority of other fetal brain abnormalities remain undiagnosed until the midtrimester. Such anomalies would be potentially detectable if the sonographic study were to be extended to include additional anatomic details not currently included in existing guidelines. The aim of this review article is to describe how best to assess the normal fetal brain by first-trimester expert multiplanar neurosonography and to demonstrate the early sonographic findings that characterize some major fetal brain abnormalities. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Intracranial Translucency, Its Use as a Potential First Trimester Ultrasound Marker for Screening of Neural Tube Defects

The objective of the study was to describe a case-series of neural tube defects (NTD) with an abnormal intracranial translucency (IT) detected during the first-trimester ultrasound scan, performed on a low-risk obstetric population in Mexico. Certified Fetal Medicine specialists performed all US scans; the IT was assessed using the mid-sagittal view of the fetal head, which is already systematically used for nuchal translucency and nasal bone evaluation. During the study, we were able to find that eight fetuses had an absence of the intracranial translucency, out of which two were reassessed at 14 weeks' gestation and IT was normal, six of them were later diagnosed to have an NTD that consisted in spina bifida aperta (n = 5) and encephalocele (n = 1). Conclusion: As previous studies have shown, IT evaluation during the first-trimester US routine scan may be a useful screening marker for early detection of NTDs.

Accuracy of qualitative and quantitative cranial ultrasonographic markers in first-trimester screening for open spina bifida and other posterior brain defects: a systematic review and meta-analysis

BACKGROUND

The significant number of qualitative and quantitative ultrasound markers described for first-trimester screening of open spina bifida (OSB) and other posterior brain defects (oPBD) has resulted in their complex implementation and interpretation for a widespread screening and in a lack of consensus regarding diagnostic accuracy.

OBJECTIVES

To assess and compare the accuracy of qualitative and quantitative cranial sonographic markers at 11-14 weeks of gestation for the detection of OSB and oPBD.

SEARCH STRATEGY

A systematic literature search was performed in MEDLINE and COCHRANE from 2009 to April 2020.

SELECTION CRITERIA

Studies assessing the diagnostic accuracy of quantitative and/or qualitative ultrasound signs to predict OSB and oPBD were included. Cohort studies and case-control studies were also considered.

DATA COLLECTION AND ANALYSIS

Two reviewers independently extracted data and assessed the risk of bias. The overall pooled estimate and a summary receiver operating characteristic curve was estimated for each subgroup (qualitative and quantitative assessment).

MAIN RESULTS

Twenty-three studies were included in our meta-analysis. The pooled sensitivity and specificity for qualitative assessment were 76.5% and 99.6%, and for quantitative assessment were 84.5% and 96.3%, respectively; specificity for the qualitative ultrasound signs was significantly higher (P = 0.001). The overall sensitivity of cranial sonographic markers for the screening of oPBD was 76.7% and specificity was 97.5%.

CONCLUSIONS

The qualitative approach demonstrated greater specificity, so this would appear to be more appropriate for daily screening, as a first-line tool, whereas the quantitative approach should be reserved for expert ultrasound.

TWEETABLE ABSTRACT

This study highlights the relevance of first-trimester qualitative ultrasound signs in the screening of open spina bifida.

Reference ranges for the fetal mesencephalon to occiput measurement at 11 to 13+6 weeks of gestation

The objective was to have a quantitative description of the normal position of the fetal midbrain in the first trimester, through defining the reference ranges for the mesencephalon to the occipital bone distance, in the axial plane. This was a prospective study that included normal fetuses screened between 11 and 13 weeks of gestation. The distance was measured between the posterior limit of the mesencephalon to the occipital bone in the same axial view as the one required for the biparietal diameter (BPD) assessment, at this gestational age (GA). The reference ranges using quantile regression, according to the crown-rump length (CRL), BPD, and GA were fitted. Data analysis included 428 ultrasound measurements. A good, linear correlation was observed between mesencephalon to occiput (MO) distance and CRL, BPD, or GA. It increased linearly with advancing gestation (log₁₀MO = -0.1834 + 0.0092 x CRL, R²=0.48, P<0.0001) and was independent of maternal demographic characteristics and intracranial translucency (IT). In our study, the 1st percentile of the normal MO distance varies from 1.31 mm at a CRL of 45 mm to 2.08 mm at a CRL of 84 mm. The intraclass correlation coefficient (ICC) was 0.89 for intraobserver variability. A significant increase in the MO distance was found in the patients who did not receive folic acid in the first trimester of pregnancy [1.056 vs. 1.008 multiple of median (MoM), P=0.014]. A simple measurement is described between the midbrain and the occipital bone, obtained in the same axial view. It increases linearly with advancing gestation. Integration of this measurement into the routine ultrasound screening in association with the ‘crash sign’ and recognizing the lower extreme values could lead to an early diagnosis of open spina bifida (OSB).

Ratio of fetal choroid plexus to head size: simple sonographic marker of open spina bifida at 11-13 weeks' gestation

OBJECTIVES

To measure the ratio of choroid plexus (CP) size to head size in normal fetuses and to compare it to that in fetuses with open spina bifida (OSB) and quantify the subjective sign of a 'dry brain'.

METHODS

This was a retrospective study of ultrasound images, obtained during first-trimester screening between 11 and 13 weeks of gestation, from 34 fetuses with OSB and 160 normal fetuses. From the hospital databases, we retrieved images of the fetal head in the transventricular axial plane. We measured the areas of both CPs and the head and calculated the ratio between them. We also measured the longest diameter of each CP and calculated their mean (CP length), and measured the occipitofrontal diameter (OFD) and calculated the ratio of CP length to OFD. Measurements from the OSB fetuses were plotted on crown-rump length (CRL) reference ranges constructed using data from the normal fetuses, and Z-scores were calculated.

RESULTS

In the normal fetuses, the CP area increased, while the ratios of CP area to head area and CP length to OFD decreased, with increasing CRL. In 30 of the 34 (88%) fetuses with OSB, both ratios were increased significantly and the CPs filled the entirety of the head, giving the impression of a dry brain. In these cases, the borders of the lateral ventricles could not be identified.

CONCLUSIONS

At 11-13 weeks, the majority of fetuses with OSB have reduced fluid in the lateral ventricles such that the CPs fill the head. The dry brain sign is easily visualized during routine first-trimester ultrasound examination while measuring the biparietal diameter, and can be quantified by comparing the size of the CPs to the head size. Until prospective data confirm the usefulness of this sign in screening for OSB, it should be considered as a hint to prompt the examiner to assess thoroughly the posterior fossa and spine. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Cranial sonographic markers of fetal open spina bifida at 11 to 13 weeks of gestation

OBJECTIVES

To compare the sonographic signs of spina bifida obtained on axial and sagittal views of the fetal head between 11 and 13+6 weeks of gestation.

METHODS

This was a retrospective study including 27 cases of spina bifida and 1003 randomly selected controls. Indirect markers of spina bifida were evaluated on stored ultrasound images. Intracranial translucency (IT), ratio between the brainstem and the brainstem-occipital bone distance (BS/BSOB), and maxillo-occipital (MO) line were assessed on sagittal view, whereas biparietal diameter (BPD), BPD to abdominal circumference ratio (BPD/AC), and aqueduct to occipital bone (aqueduct of Sylvius [AoS]) distance were measured on the axial plane. Reference ranges were developed, and cases of spina bifida were examined in relation to the reference range.

RESULTS

On the sagittal view, detection rates for IT below the fifth percentile, BS/BSOB above the 95th percentile, and an abnormal MO line were 52.3%, 96.3%, and 96.3%, respectively. On the axial view, detection rates for BPD, BPD/AC, and AoS below the fifth percentile were 66.7%, 70.4%, and 77.8%, respectively.

CONCLUSION

The MO line and the BS/BSOB ratio appear to be the best indirect ultrasound markers of spina bifida and can be easily obtained during the routine first-trimester scan.

Crash sign: new first-trimester sonographic marker of spina bifida

OBJECTIVES

To describe a new first-trimester sonographic sign, the 'crash sign', associated with fetal open spina bifida, and to evaluate its clinical usefulness in the first-trimester diagnosis of spina bifida.

METHODS

This was a retrospective review of patients referred to three fetal medicine centers in the first trimester (11 + 0 to 13 + 6 weeks) with suspected spina bifida. Spina bifida was confirmed by direct visualization of the spinal defect on ultrasound by two experts and, when possible, by fetal postmortem examination. Ultrasound images were reviewed for the presence of the crash sign, which is the posterior displacement of the mesencephalon and deformation against the occipital bone in the axial view. The first-trimester ultrasound images of a mixed group of 10 cases and 40 control fetuses without spina bifida were assessed for the presence of the crash sign by two assessors blinded to the diagnosis.

RESULTS

The crash sign was present in 48 out of 53 confirmed cases of spina bifida. Of these, 27 had isolated spina bifida and 21 had an associated anomaly. Of the five cases without the crash sign, one had isolated spina bifida and four had an associated anomaly. The crash sign was not reported in any of the control fetuses.

CONCLUSIONS

We have described a new first-trimester sonographic marker for the diagnosis of spina bifida. Our results suggest that the crash sign may be a useful tool in the first-trimester detection of spina bifida. Prospective evaluation of the crash sign would be beneficial, ideally in a routine clinical screening ultrasound setting. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Maxillo-occipital line: a sonographic marker for screening of open spina bifida in the first trimester of pregnancy

Objective: To describe a new first-trimester sonographic landmark the maxillo-occipital line which may be useful for early screening of open spina bifida.Methods: Maxillo-occipital line was prospectively evaluated in 100 low-risk pregnancies at the time of first-trimester sonographic screening examination between 11 and 13 + 6 weeks' gestation. All the pregnant women subsequently had a normal second-trimester scan and normal outcomes. Midsagittal brain images of 14 fetuses with known diagnosis of open spina bifida were evaluated retrospectively to review the maxillo-occipital line.Results: None of the 100 fetuses evaluated prospectively with the maxillo-occipital line below the junction of the midbrain and brain stem were affected by open spina bifida. The aqueduct of Silvius to occiput distance measurement was not obtained in five cases. In all, 14 cases with a diagnosis of open spina bifida, the junction between the midbrain and brain stem, were below the maxilla-occipital line.Conclusion: Maxillo-occipital line is an easy addition to the evaluation of first-trimester screening of open spina bifida. Further studies are needed to determine the false-positive and false-negative rates of this technique.

Non-visualization of choroid plexus of fourth ventricle as first-trimester predictor of posterior fossa anomalies and chromosomal defects

OBJECTIVE

To assess non-visualization of the choroid plexus of the fourth ventricle (CP-4V) as a simple, qualitative and reproducible first-trimester ultrasound feature of the posterior fossa for the prediction of central nervous system (CNS) anomalies and chromosomal defects.

METHODS

First-trimester three-dimensional ultrasound datasets of the fetal brain were obtained prospectively from 65 consecutive normal singletons and retrospectively from 27 fetuses identified as having an abnormal posterior fossa on first-trimester ultrasound examination, and randomly combined to form the final study group. The stored ultrasound volumes were analyzed offline by two accredited sonologists, who were not aware of the final diagnoses. The CP-4V was assessed by multiplanar navigation and classified as visible or non-visible in its normal position depending on whether or not the echogenic structure that separates the fourth ventricle from the cisterna magna was identified in both midsagittal and axial planes. Correlation with subsequent second-trimester ultrasound, fetal magnetic resonance imaging, or postmortem or postnatal findings was performed to determine the predictive value of the first-trimester findings.

RESULTS

Among the 92 ultrasound datasets analyzed, 73 (79%) were acquired transabdominally and 19 (21%) transvaginally. The CP-4V was classified as visible in 64 cases and non-visible in 28 cases, with agreement between the two observers in both sagittal and axial planes in all but one case. Twelve of the 28 (43%) fetuses with non-visible CP-4V were subsequently diagnosed as having a CNS malformation (open spina bifida (n = 6), Dandy-Walker malformation (n = 2), Blake's pouch cyst (n = 2), cephalocele (n = 1) and megacisterna magna (n = 1)). In addition, 20 of these 28 (71%) fetuses had aneuploidy (trisomy 18 (n = 10), triploidy (n = 5), trisomy 13 (n = 3), Turner syndrome (n = 1) or trisomy 21 (n = 1)). There was only one false-positive case, in which the CP-4V was classified as absent in a normal fetus.

CONCLUSIONS

Non-visualization of the CP-4V in the first trimester appears to be a strong marker of posterior fossa anomalies and chromosomal defects. Qualitative evaluation of this anatomic structure is simple, feasible and reproducible, and its routine assessment during the first-trimester scan may facilitate the early detection of CNS anomalies and associated fetal aneuploidy. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Sonographic detection of open spina bifida in the first trimester: review of the literature

In the beginnings, sonographic diagnosis of open spina bifida (OSB) relied on the meticulous scanning of the fetal vertebrae for abnormalities but many defects were missed. After the mid-1980s, however, with the description of the intracranial findings in the second trimester (the "lemon sign" and the "banana sign"), the prenatal diagnosis of OSB was enhanced. In the last 2 decades, there has been widespread uptake of routine ultrasound examination in the first trimester of pregnancy with the purpose of the measurement of fetal crown-rump length to determine gestational age, to screen for trisomy 21 and other aneuploidies, mainly with the nuchal translucency, and for diagnosis of many major abnormalities. Many papers were published focusing on early diagnosis of myelomeningocele (MMC), and the objective of this review is to summarize the different techniques described regarding prenatal diagnosis of OSB in the first trimester of pregnancy.

Prenatal diagnosis of spina bifida: from intracranial translucency to intrauterine surgery

Accurate and timely prenatal diagnosis of spina bifida (SB) is a major goal of modern antenatal care. Prenatal screening for open SB should be first performed at the time of routine first-trimester ultrasound by examining the posterior fossa for obliteration or non-visualization of the fourth ventricle ("intracranial translucency") and cisterna magna. The second step of screening is the second-trimester anatomy scan, at which time the features of the Chiari type II malformation should be looked for, including ventriculomegaly, scalloping of the frontal bones ("lemon" sign), and backward and caudal displacement of the cerebellar vermis with obliteration of the cisterna magna ("banana" sign). In cases with positive findings, evaluation must include a focused examination of the spine for defects. In cases of closed SB and SB occulta, the cranial and posterior fossa features will not be present as they are not associated with leaking of spinal fluid and resultant hindbrain herniation, highlighting the fact that the spine should be examined thoroughly whenever possible during the second-trimester scan. In tertiary fetal medicine centers, two-dimensional and three-dimensional ultrasound allows an accurate determination of the location, type, extent, and upper level of the spinal defect as well as the presence of associated anomalies. Fetal magnetic resonance imaging should be restricted to candidates for intrauterine surgery as part of the preoperative protocol.

Towards Detecting Open Spina Bifida in the First Trimester: The Examination of the Posterior Brain

Introduction: Our aim was to examine the value of indirect signs of open spina bifida in the mid-sagittal view of the posterior brain at the 11-13 weeks' ultrasound examination and to summarize the current evidence for the first-trimester diagnosis of spina bifida. Methods: This was a prospective study in routine obstetric population. The presence of four almost parallel lines (four-line view) in the posterior brain was recorded. Biparietal diameter (BPD), intracranial translucency (IT) and cisterna magna (CM) were measured. The ratio of IT to CM (R ratio) was calculated. Results: 2,491 pregnancies were examined prospectively. Updated reference ranges for IT and CM were constructed. There were 3 cases with open spina bifida, and the four-line view was abnormal in 2 of them. The abnormal fetuses had smaller BPD as well as pronounced reduction in the CM and increase in the R ratio. Discussion: Examination of the posterior brain was feasible in all fetuses in the setting of the routine 11-13 weeks' ultrasound examination. Indirect signs of spina bifida are visible in the mid-sagittal view of the posterior brain, and the assessment of these structures can be a reliable tool in the early identification of this abnormality.

Fluid Area Measurements in the Posterior Fossa at 11-13 Weeks in Normal Fetuses and Fetuses with Open Spina Bifida

Objectives: To measure the area of the intracranial translucency (IT) (syn: 4th ventricle) and the future cisterna magna (CM) in normal fetuses and to compare with fetuses with open spina bifida. Patients: In the midsagittal plane of the face of 220 fetuses between 11 and 13 weeks' gestation, the areas of the IT and CM were measured and the sum, defined as the posterior fossa fluid (PFF) area was calculated. Reference ranges were constructed in relation to the crown-rump length. The study group consisted of 21 fetuses with open spina bifida and showed in all cases a single pocket of fluid in the posterior fossa. Fetuses with no fluid in the fossa were excluded. This PFF-area was measured and compared with the reference range of the IT-area and the PFF-area of normal fetuses and Z-scores were calculated. Results: In normal fetuses, a significant increase of the IT-, the CM- and the PFF-area was found as a sign of the expanding posterior fossa. The mean PFF-area increased from 8.55 to 29.72 mm2 in the observation period. Fetuses with open spina bifida had reduced fluid in the posterior fossa with values ranging between 2.39 and 5.08 mm2 and significantly lower Z-scores. Conclusions: Fetuses with open spina bifida have an abnormally small posterior fossa at 11-13 weeks' and in cases where the cerebrospinal fluid is still present, the fluid area in the midsagittal plane is reduced when compared to normal fetuses. Area fluid assessment can be an additional useful measurement in suspicious cases for open spina bifida in early gestation.

Detection of structural abnormalities in the first trimester using ultrasound

During the past 25 years, embryonic and early fetal ultrasound and diagnosis have increasingly gained attention in pregnancy care. Modern high-frequency ultrasound transducers make it possible to obtain detailed images of the early conceptus and its organs, and thus move part of the anatomy and anomaly scan from the second to the first trimester. Today, detection of embryonic and fetal structural abnormalities in the first trimester has frequently been reported. One has to distinguish between diagnosis during the early period until about 10 weeks when the embryo or early fetus is small and transvaginal ultrasound is applied, and diagnosis during the late period at the nuchal translucency screening, usually carried out using transabdominal ultrasound. Early first-trimester abnormalities are often diagnosed by chance on clinical indications, whereas late first-trimester diagnoses are the result of systematic screening using ultrasound markers.

Cisterna magna width at 11-13 weeks in the detection of posterior fossa anomalies

OBJECTIVE

To construct reference ranges for cisterna magna (CM) width at 11-13 weeks' gestation in healthy fetuses and determine whether open spina bifida and posterior fossa anomalies could be diagnosed in the first trimester.

METHODS

This was a retrospective study. CM width reference ranges were constructed based on the measurements obtained from 80 healthy fetuses with normal postnatal outcome undergoing routine first-trimester ultrasound at 11-13 weeks, using the Lambda-Mu-Sigma method. CM was measured in the fetal mid-sagittal view, as routinely used for nuchal translucency assessment. In addition, first-trimester ultrasound images in 11 fetuses with open spina bifida or posterior fossa anomalies, most of which were diagnosed later in pregnancy, were retrospectively reviewed, and CM measurements were compared against reference ranges.

RESULTS

CM width was noted to increase with gestational age in normal fetuses. The anomalies in the 11 fetuses we reviewed were: open spina bifida (n = 5), megacisterna magna (n = 3), Blake's pouch cyst (n = 2) and posterior fossa arachnoid cyst (n = 1). All fetuses with open spina bifida had a CM width below the 5(th) percentile. In the two fetuses with Blake's pouch cyst and in two with megacisterna magna, CM width was above the 95(th) percentile. In one of the fetuses with a megacisterna magna and the one with an arachnoid cyst, CM width was within normal range.

CONCLUSION

We have constructed reference ranges for CM width at 11-13 weeks using the mid-sagittal view. It appears that first-trimester CM width can be used as a marker for the early detection of open spina bifida. However, our findings need to be confirmed in prospective large series.

Screening for fetal spina bifida by ultrasound examination in the first trimester of pregnancy using fetal biparietal diameter

OBJECTIVE

Prenatal screening for aneuploidies is best achieved in the first trimester when there is no reliable screening test for spina bifida. Early ultrasound features may be too complex for routine screening. We assessed screening potential of simple and reproducible fetal biometric measurements at 11-14 weeks of gestation.

STUDY DESIGN

A total of 34,951 unselected consecutive pregnancies included 18 with spina bifida. Another 28 cases were referred for assessment. Biometric measurements were expressed in multiples of the median for crown-rump length.

RESULTS

Biparietal diameter (BPD) was smaller in spina bifida (P < .0001). In all, 22 of 44 (50%) cases with spina bifida aperta had a BPD <5th centile. BPD was independent of maternal adiposity and smoking status.

CONCLUSION

Simple and reproducible BPD at 11-14 weeks of gestation could detect half the cases of open fetal spina bifida by identifying 5% of pregnancies for expert scanning in first- and second-trimester examinations of the fetal spine and cranium.

Small biparietal diameter in fetuses with spina bifida on 11-13-week and mid-gestation ultrasound

OBJECTIVES

To assess whether, at 11-13-week and mid-trimester ultrasound examinations, the biparietal diameter (BPD) in fetuses with open spina bifida is smaller than the reference range.

METHODS

In a multicenter retrospective analysis of data from 23 fetuses with open spina bifida diagnosed at 16-24 weeks, BPD at diagnosis was compared with that measured at 11-13 weeks, before diagnosis. Z-scores were calculated for comparison of BPD deviations from the reference range within the groups at 11-13 weeks and 16-24 weeks, and between these two time intervals.

RESULTS

BPD Z-scores at 11-13 weeks and 16-24 weeks were significantly lower (P < 0.0001) in fetuses with open spina bifida when compared to the reference range, with mean values of - 1.29 and - 2.14, respectively, corresponding to the 10(th) and 1.5(th) centiles, respectively. At 11-13 weeks only six of the 23 (26%) fetuses with open spina bifida had BPD below the 5(th) centile, in comparison to 16 (69%) at mid-gestation. This was confirmed by paired t-test comparing the first-trimester with the second-trimester BPD measurements, which showed significantly slower growth of the BPD in fetuses with spina bifida.

CONCLUSION

In fetuses with open spina bifida, BPD is smaller not only in the second trimester, as previously reported, but also in the first trimester. This is most likely due to loss of cerebrospinal fluid. We suggest that a BPD value < 10(th) centile in an otherwise normally grown fetus at 11-13 weeks' gestation should be considered as a potential subtle early marker for open spina bifida.

Early fetal anatomical sonography

Over the past decade, prenatal screening and diagnosis has moved from the second into the first trimester, with aneuploidy screening becoming both feasible and effective. With vast improvements in ultrasound technology, sonologists can now image the fetus in greater detail at all gestational ages. In the hands of experienced sonographers, anatomic surveys between 11 and 14 weeks can be carried out with good visualisation rates of many structures. It is important to be familiar with the normal development of the embryo and fetus, and to be aware of the major anatomical landmarks whose absence or presence may be deemed normal or abnormal depending on the gestational age. Some structural abnormalities will nearly always be detected, some will never be and some are potentially detectable depending on a number of factors.