Examination of the fetal brain by transabdominal three-dimensional ultrasound: potential for routine neurosonographic studies

Sonographic Cortical Development and Anomalies in the Fetus: A Systematic Review and Meta-Analysis

The aim of this systematic review is to report the normal cortical development of different fetal cerebral fissures on ultrasound, describe associated anomalies in fetuses with cortical malformations, and evaluate the quality of published charts of cortical fissures. The inclusion criteria were studies reporting development, anomalies, and reference charts of fetal cortical structures on ultrasound. The outcomes observed were the timing of the appearance of different cortical fissures according to different gestational age windows, associated central nervous system (CNS) and extra-CNS anomalies detected at ultrasound in fetuses with cortical malformation, and rate of fetuses with isolated anomaly. Furthermore, we performed a critical evaluation of the published reference charts for cortical development on ultrasound. Random-effect meta-analyses of proportions were used to combine the data. Twenty-seven studies (6875 fetuses) were included. Sylvian fissure was visualized on ultrasound in 97.69% (95% CI 92.0-100) of cases at 18-19, 98.17% (95% CI 94.8-99.8) at 20-21, 98.94% (95% CI 97.0-99.9) at 22-23, and in all cases from 24 weeks of gestation. Parieto-occipital fissure was visualized in 81.56% (95% CI 48.4-99.3) of cases at 18-19, 96.59% (95% CI 83.2-99.8) at 20-21, 96.85% (95% CI 88.8-100) at 22-23, and in all cases from 24 weeks of gestation, while the corresponding figures for calcarine fissure were 37.27% (95% CI 0.5-89.6), 80.42% (95% CI 50.2-98.2), 89.18% (95% CI 74.0-98.2), and 96.02% (95% CI 96.9-100). Malformations of cortical development were diagnosed as an isolated finding at ultrasound in 6.21% (95% CI 2.9-10.9) of cases, while they were associated with additional CNS anomalies in 93.79% (95% CI 89.1-97.2) of cases. These findings highlight the need for large studies specifically looking at the timing of the appearance of the different brain sulci. Standardized algorithms for prenatal assessment of fetuses at high risk of malformations of cortical development are also warranted.

Reference ranges of fetal cisterna magna volume measurements by three-dimensional ultrasonography in the late second trimester considering sonographic experience

BACKGROUND

Volume measurements of fetal cisterna magna (CM) by three-dimensional (3D) ultrasonography may have a role in the diagnosis of various posterior fossa abnormalities.

PURPOSE

To evaluate reference intervals and reliability of fetal CM volume values by virtual organ computer-aided analysis (VOCAL) in structurally normal fetuses, considering experience of evaluators.

MATERIAL AND METHODS

Three operators with different 3D sonography experience levels measured CM volumes of 100 structurally normal fetuses at 18-27 weeks of gestation. Reference intervals for CM volumes were generated. Intraclass correlation coefficients (ICC) were calculated.

RESULTS

Mean fetal CM volume measurements by the three operators did not significantly (P = 0.49, P = 0.22, and P = 0.17, respectively) change through 20-23 weeks of gestation. Moderate degrees of inter-observer reliability were found with an ICC of 0.69 between novice and intermediate-level, ICC of 0.74 between experienced and intermediate-level, and ICC of 0.78 between experienced and novice observer, respectively. The novice sonographer generally overestimated CM measurements. Intra-observer reliability was good (ICC=0.85).

CONCLUSION

A reference chart for fetal CM volume by VOCAL was formed, revealing uniform mean values of 20-23 weeks of gestation. The inter-observer reliability is moderate, and biases seem relatively common for all experience categories.

Should 3D volume assessment of the corpus callosum and cerebellar vermis be a part of a routine second trimester screening?

BACKGROUND

The majority of fetal structural defects can be detected in the second trimester, thus this is the main time for screening for structural defects. 3D imaging of the fetal brain does not create a common part of this screening.

METHODS

This prospective observational study was conducted at the Fetal Medicine Center of The Gynecological-Obstetrical Department of the University Hospital Olomouc in years 2017-2020. The study sample was 451 consecutively scanned morphologically normal fetuses attending for routine second trimester anatomical survey at 20-22 weeks of pregnancy. A transabdominal 3D ultrasound volume acquisition of fetal brain was obtained from an axial and sagittal plane using skull sutures as an acoustic window.

RESULTS

Both the corpus callosum (CC) and the vermis (VC) were detected in 51.7% of examinations in the sagittal plane, and in 31.7% in the axial plane. In 61.9% of the examinations, there was at least partial detection in both planes. Maternal BMI was found to be the only significant predictor of the quality of imaging in both planes.

CONCLUSION

3D acquisition of fetal brain images in the sagittal plane followed by manipulation of acquired volume was valuable in assessment of corpus callosum and cerebellar vermis. This allows reconstruction of the sagittal plane that can be difficult to obtain in 2D imaging.

Automatic measurements of fetal intracranial volume from 3D ultrasound scans

Three-dimensional fetal ultrasound is commonly used to study the volumetric development of brain structures. To date, only a limited number of automatic procedures for delineating the intracranial volume exist. Hence, intracranial volume measurements from three-dimensional ultrasound images are predominantly performed manually. Here, we present and validate an automated tool to extract the intracranial volume from three-dimensional fetal ultrasound scans. The procedure is based on the registration of a brain model to a subject brain. The intracranial volume of the subject is measured by applying the inverse of the final transformation to an intracranial mask of the brain model. The automatic measurements showed a high correlation with manual delineation of the same subjects at two gestational ages, namely, around 20 and 30 weeks (linear fitting R2(20 weeks) = 0.88, R2(30 weeks) = 0.77; Intraclass Correlation Coefficients: 20 weeks=0.94, 30 weeks = 0.84). Overall, the automatic intracranial volumes were larger than the manually delineated ones (84 ± 16 vs. 76 ± 15 cm3; and 274 ± 35 vs. 237 ± 28 cm3), probably due to differences in cerebellum delineation. Notably, the automated measurements reproduced both the non-linear pattern of fetal brain growth and the increased inter-subject variability for older fetuses. By contrast, there was some disagreement between the manual and automatic delineation concerning the size of sexual dimorphism differences. The method presented here provides a relatively efficient way to delineate volumes of fetal brain structures like the intracranial volume automatically. It can be used as a research tool to investigate these structures in large cohorts, which will ultimately aid in understanding fetal structural human brain development.

Fetal neurosonography at 31-35 weeks reveals altered cortical development in pre-eclampsia with and without small-for-gestational-age fetus

OBJECTIVE

To explore the pattern of fetal cortical development in pregnancies complicated by pre-eclampsia (PE), with and without a small-for-gestational-age (SGA) fetus, compared to uncomplicated pregnancies.

METHODS

This was a prospective observational study including singleton pregnancies complicated by normotensive SGA (birth weight < 10^th centile) (n = 77), PE with an appropriate-for-gestational-age (AGA) fetus (n = 76) or PE with a SGA fetus (n = 67), and 128 uncomplicated pregnancies (normotensive AGA) matched by gestational age at ultrasound. All pregnancies underwent detailed neurosonography, using a transabdominal and transvaginal approach, at 31-35 weeks' gestation to assess the depth of the insula, Sylvian fissure, parieto-occipital sulcus, cingulate sulcus and calcarine sulcus. All measurements were adjusted for biparietal diameter (BPD). In addition, a grading score of cortical development was assigned to each brain structure, ranging from Grade 0 (no development) to Grade 5 (maximum development). Univariate and multiple regression analyses were conducted.

RESULTS

Similar to findings in previous studies, normotensive pregnancies with a SGA fetus showed significant differences in cortical development compared with controls, with reduced Sylvian fissure depth adjusted for BPD (14.5 ± 2.4 vs 16.6 ± 2.3; P < 0.001) and increased insula depth adjusted for BPD (33.2 ± 2.0 vs 31.8 ± 2.0; P < 0.001). Interestingly, a similar cortical development pattern was observed in PE pregnancies with a SGA fetus and in PE pregnancies with an AGA fetus, manifested by reduced Sylvian fissure depth adjusted for BPD (14.2 ± 2.3 and 14.3 ± 2.3 vs 16.6 ± 2.3; P < 0.001 for both) and greater insula depth adjusted for BPD (33.2 ± 2.1 and 32.8 ± 1.7 vs 31.8 ± 2.0; P < 0.001 for both) compared with controls. No significant differences were observed in parieto-occipital, cingulate sulcus or calcarine sulcus depth across the study groups. The Sylvian fissure was scored as Grade 4 in significantly more (93.2% vs 59.5%) and as Grade 5 in significantly fewer (2.7% vs 37.3%) PE pregnancies with an AGA fetus compared with controls (P < 0.05 for both). These differences remained significant even after statistical adjustment for potential confounders, including ethnicity, low socioeconomic status, nulliparity, chronic hypertension, pregestational diabetes, assisted reproductive technologies, smoking and fetal gender, with the application of Benjamini-Hochberg procedure for multiple comparisons.

CONCLUSIONS

PE with or without SGA is associated with a differential fetal cortical development pattern which is similar to that described previously in small fetuses. Future research is warranted to elucidate better the mechanism(s) underlying these changes. © 2022 International Society of Ultrasound in Obstetrics and Gynecology.

Fetal brain imaging: A comparison between fetal ultrasonography and intra uterine magnetic resonance imaging (a systematic review and meta-analysis)

OBJECTIVE

The aim of this study was to compare ultrasound (US) and intra uterine MRI (IUMRI) of the brain in the diagnosis of fetal brain abnormalities.

METHODS

The present systematic review is done based on guidelines for preferred reporting items for systematic reviews and meta-analysis. All major articles comparing fetal US with IUMRI in fetuses with suspected brain abnormalities were qualified. Articles published before 2010 were excluded from the study. An I²  > 20% was considered as a sign of significant change. The statistical analysis was done using STATA -15 and Meta-Disk 1.4 applications.

RESULTS

Five articles were considered for meta-analysis. The sensitivity of US and IUMRI in diagnosing fetal abnormalities were 86% and 95%, respectively. The corresponding rates for specificity were 77% and 80%. IUMRI and US were concordant in 72.5% (95% CI: 68%-77%) of diagnoses. However, IUMRI added information in 21.7% of cases, while US added value was only 1.48.

CONCLUSION

Our results approved the good diagnostic performance of both US and IUMRI in confirming fetal brain normal development and emphasized that US is an appropriate screening technique in pregnancy. In cases of detected abnormalities in US, IUMRI is suggested as it was the most accurate imaging method and added information about the diagnosis in 22.2% of cases.

3-Dimensional Ultrasound: How can the Fetal Corpus Callosum Be Demonstrated Correctly?

The aim of this article is to outline the correct demonstration of the fetal corpus callosum with 3D ultrasound between 18 and 40 weeks of gestation. An abdominal or transvaginal 3D transducer can be used for acquisition of the fetal brain depending on the position of the fetus. The best demonstration of the corpus callosum can be achieved, when the volume with the corpus callosum is acquired from a sagittal or parasagittal sectional plane of the brain. Once the volume is stored in the memory, the multiplanar mode allows manipulation in all three dimensions until the exact median plane is seen, showing the corpus callosum as a hypo- or anechoic curved structure. Volume acquisition of the brain from an axial plane of the fetal head - typically used for biometrical measurements of the head diameters - is not recommended for clinical evaluation of the corpus callosum because the reconstructed median plane does not reveal the margins and the structure of the corpus callosum precisely. Other display modes such as volume contrast imaging (VCI), OmniView-VCI, and tomographic display may also be used for demonstration of the corpus callosum. However, these display modes only provide the operator with good image quality of the corpus callosum if the fetal brain was acquired from a sagittal and not from an axial plane. CONCLUSION:  3D ultrasound is an excellent clinical tool for the exact presentation of the fetal corpus callosum because it allows volume manipulation of the fetal head in all three dimensions with precise demonstration of the median plane of the brain.

Assessing lateral uterine wall defects and residual myometrial thickness after cesarean section

OBJECTIVE

Lateral wall ruptures in women with a history of cesarean section are less common but more complicated than anterior wall ruptures. Residual myometrial thickness (RMT) is believed to be valuable for assessing the probability of ruptures. This study aimed to assess the utility of OmniView (a sonographic reslicing technique) in evaluating the lateral uterine wall after cesarean section and evaluate the relationship between lateral and anterior wall RMT using OmniView and sagittal two-dimensional ultrasound.

STUDY DESIGN

This cross-sectional study examined changes in both the anterior and lateral uterine wall in women with a history of cesarean section in the past 12-18 months. OmniView with volume contrast imaging with a 2-mm slice thickness was used to generate coronal planes, and the OmniView RMT (OV-RMT) was calculated as a percentage. Blinded to the OV-RMT results, sonographic multiplanar views were used to acquire the optimum sagittal plane for evaluating the RMT, and the sagittal RMT (S-RMT) was calculated as a percentage. The reproducibility of OV-RMT and S-RMT between two observers was tested using interclass correlation (ICC). The relationship between two variables was tested using Spearman's rank correlation.

RESULTS

In 208 recruited patients, the prevalence of lateral uterine wall defects was 79 %. The interobserver and intraobserver reproducibility of S-RMT and OV-RMT had ICC coefficients over 0.9 with a p-value <0.001. S-RMT and OV-RMT did not follow a normal distribution, and the medians were significantly different (55.5 and 85.7, respectively). Spearman's rank correlation between OV-RMT and S-RMT had a rho (ρ) value of 0.24 (p < 0.05). Passing-Bablok regression had an intercept of 47.95 and a slope of 0.65.

CONCLUSION

OmniView can be used to assess lateral uterine wall defects, and OV-RMT is a reproducible and reliable method for quantifying this assessment. The RMT on the coronal plane was independently more intact than that on the sagittal plane, which might account for the lower incidence of lateral ruptures. Further studies could reveal a critical OV-RMT value that is safe for a trial of labor.

Brain views that benefit from three-dimensional ultrasound

PURPOSE OF REVIEW

Fetal central nervous system malformations are among the most common congenital anomalies. Whereas simple axial views are sufficient for basic fetal brain examination, other important views are essential for a more detailed examination, which are sometimes challenging to obtain. Three-dimensional ultrasound can be helpful in obtaining standardized and reproducible images of many difficult fetal brain views. The aim of the present review is to explore the most recent evidence on the utility and technique of three-dimensional ultrasound in the examination of the fetal brain, with particular emphasis on the brain views that benefit from three-dimensional ultrasound.

RECENT FINDINGS

The article describes the various techniques of acquisition and analyses of three-dimensional ultrasound volumes of the fetal brain and their usefulness in the assessment of normal and abnormal fetal brain anatomy. Three-dimensional ultrasound has also permitted the application of many new technologies, such as artificial intelligence and deep machine learning. Recently, thanks to high-quality three-dimensional ultrasound, fetal cortical development can be assessed quantitatively and reliably.

SUMMARY

Three dimensional ultrasound can help as a complementary tool to two-dimensional ultrasound in the assessment of the fetal brain development and malformations. In addition, it paves the way for the application of promising technologies in the evaluation of fetal brain.

VIDEO ABSTRACT

A video summarizing the findings of the article. The video illustrates the various approaches and techniques applied for the examination of the fetal brain using three-dimensional ultrasound. Furthermore, the advantages and future perspectives of the application of three-dimensional ultrasound in the examination of the fetal brain are discussed, http://links.lww.com/COOG/A74.

Towards automated extraction of 2D standard fetal head planes from 3D ultrasound acquisitions: A clinical evaluation and quality assessment comparison

Introduction

Clinical evaluation of deep learning (DL) tools is essential to compliment technical accuracy metrics. This study assessed the image quality of standard fetal head planes automatically-extracted from three-dimensional (3D) ultrasound fetal head volumes using a customised DL-algorithm.

Methods

Two observers retrospectively reviewed standard fetal head planes against pre-defined image quality criteria. Forty-eight images (29 transventricular, 19 transcerebellar) were selected from 91 transabdominal fetal scans (mean gestational age = 26 completed weeks, range = 20⁺⁵–32⁺³ weeks). Each had two-dimensional (2D) manually-acquired (2D-MA), 3D operator-selected (3D-OS) and 3D-DL automatically-acquired (3D-DL) images. The proportion of adequate images from each plane and modality, and the number of inadequate images per plane was compared for each method. Inter and intra-observer agreement of overall image quality was calculated.

Results

Sixty-seven percent of 3D-OS and 3D-DL transventricular planes were adequate quality. Forty-five percent of 3D-OS and 55% of 3D-DL transcerebellar planes were adequate.

Seventy-one percent of 3D-OS and 86% of 3D-DL transventricular planes failed with poor visualisation of intra-cranial structures. Eighty-six percent of 3D-OS and 80% of 3D-DL transcerebellar planes failed due to inadequate visualisation of cerebellar hemispheres. Image quality was significantly different between 2D and 3D, however, no significant difference between 3D-modalities was demonstrated (p < 0.005). Inter-observer agreement of transventricular plane adequacy was moderate for both 3D-modalities, and weak for transcerebellar planes.

Conclusion

The 3D-DL algorithm can automatically extract standard fetal head planes from 3D-head volumes of comparable quality to operator-selected planes. Image quality in 3D is inferior to corresponding 2D planes, likely due to limitations with 3D-technology and acquisition technique.

Implications for practice

Automated image extraction of standard planes from US-volumes could facilitate use of 3DUS in clinical practice, however image quality is dependent on the volume acquisition technique.

Three-dimensional ultrasonography for advanced neurosonography (neurosofe-3D): Validation of a brain volume acquisition guideline

INTRODUCTION

This study aimed to evaluate the quality of the brain volumes acquired following an evidence-based guideline for the acquisition of brain volumes.

MATERIAL AND METHODS

This was a prospective multicenter study. Five centers recruited five cases each, acquiring two volumes per case, at different gestational age ranges. From the collected volumes, 10 operators performed an advanced neurosonography of each case. The evaluable anatomic structures were counted in each volume and expressed as a percentage. The results were compared with those obtained in a previous study where no recommendations had been made for the acquisition of the volumes.

RESULTS

Five hundred evaluations were included in the study. In the axial plane, 91.5% of the structures were satisfactorily evaluated, 81.8% in the coronal plane and 89.9% in the sagittal plane. These results were significantly better than those obtained in a previous study where the volumes had been acquired without any guidelines and the percentage of evaluable structures were 80% (P < .001), 67.1% (P < .001) and 55.1% (P < .001) in the axial, coronal and sagittal planes, respectively.

CONCLUSIONS

The application of an evidence-based guideline for the acquisition of brain volumes improves the quality of these by increasing the number of evaluable structures in the volume.

Fetal Ultrasound and Magnetic Resonance Imaging Findings in Suspected Septo-Optic Dysplasia: A Diagnostic Dilemma

OBJECTIVES

To investigate prenatal imaging findings supporting a diagnosis of suspected septo-optic dysplasia (SOD) by fetal ultrasound (US), magnetic resonance imaging (MRI), or both.

METHODS

A retrospective review identified 11 patients with SOD: 9 had a clinical diagnosis of SOD postnatally, and 2 were terminated on the basis of suspicious prenatal imaging. Prenatal and neonatal imaging of the cavum septi pellucidi (CSP), frontal horns (FHs), and lateral ventricles was evaluated.

RESULTS

The appearance of the CSP varied on US and MRI. Complete ("fused") FHs or partial absence of the CSP was reported in 6 of 11 patients by fetal US and 7 of 8 patients by fetal MRI. The diagnosis of SOD was prospectively suspected prenatally in 6 of 11 and in an additional 5 of 11 cases retrospectively. Fetal MRI incorrectly initially reported normal morphologic abnormalities for 2 cases with partial absence of the CSP, whereas US accurately identified the morphologic abnormalities in 1 of these cases before MRI. Imaging features were first suggested at anatomic US (4 patients) and follow-up prenatal US (2 patients). Neonatal imaging was concordant in all 9 live births: 5 completely absent CSP, 3 partially absent CSP, and 1 completely present CSP. Clinical manifestations included optic nerve hypoplasia (9 of 9), panhypopituitarism (5 of 9), and neurodevelopmental delays.

CONCLUSIONS

Primary imaging features of SOD are "continuous" FHs with complete or partial absence of the CSP. Septo-optic dysplasia can be suspected in utero and can appear isolated but has substantial associated central nervous system anomalies identified on fetal MRI or after birth. Partial absence of the CSP can be a prenatal sign of suspected SOD, although fetal MRI lacked the spatial resolution to identify it accurately in all cases.

3D evaluation of fetal brain structures: reference values and growth curves

Background: The development of the fetal central nervous system is one of the most important fields of research in perinatology. Since the early 1980s, 3 D ultrasound has become one of the major research tools in obstetrics and gynecology.Objective: The aim of this study was to reconstruct thalamus, cerebellum and Cortex volumes of fetal brain and generate, for these volumes, growth curves related to gestational age.Methods: We enrolled 344 pregnant women. Using "Tomographic Ultrasound Imaging" (TUI), in all cases we obtained a satisfying 3 D acquisition of fetal brain. We reconstructed offline thalamus, cerebellum and cortex volumes using "Virtual Organ Computer-Aided AnaLysis" (VOCAL) or 4 D View (GE Healthcare).Results: Among the 344 fetuses examined, we obtained 314 thalamus volumes, 252 cerebellum volumes and 261 cortex volumes and we constructed the reference growth curves.Conclusion: Our study confirms the reliability of cerebral volumes evaluation using 3 D technology and how these cerebral structures grow through gestation.

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

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

Intra- and interobserver agreement for fetal cerebral measurements in 3D-ultrasonography

The aim of this study is to evaluate intra- and interobserver agreement for measurement of intracranial, cerebellar, and thalamic volume with the Virtual Organ Computer-aided AnaLysis (VOCAL) technique in three-dimensional ultrasound images, in comparison to two-dimensional measurements of these brain structures. Three-dimensional ultrasound images of the brains of 80 fetuses at 20-24 weeks' gestational age were obtained from YOUth, a Dutch prospective cohort study. Two observers performed offline measurement of the occipitofrontal diameter, intracranial volume, transcerebellar diameter, cerebellar volume, and thalamic width, area, and volume, independently. VOCAL was used for calculation of the volumes. The two-way random, single measures intraclass correlation coefficient (ICC) was used for analysis of agreement and Bland-Altman plots were configured. Intra- and interobserver agreement was almost perfect for occipitofrontal diameter (intra ICC 0.88, 95% CI 0.82-0.92; inter ICC 0.91, 95% CI 0.85-0.94), intracranial volume (intra ICC 0.96, 95% CI 0.91-0.98; inter ICC 0.97, 95% CI 0.96-0.98) and transcerebellar diameter (intra ICC 0.91, 95% CI 0.86-0.94; inter ICC 0.86, 95% CI 0.78-0.910). For cerebellar volume, the intraobserver agreement was almost perfect (0.85, 95% CI 0.76-0.90), whereas the interobserver agreement was substantial (0.75, 95% CI 0.44-0.88). Agreement was only moderate for thalamic measurements. Bland-Altman plots for the volume measurements are normally distributed with acceptable mean differences and 95% limits of agreement. The intra- and interobserver agreement of the measurement of intracranial and cerebellar volume with VOCAL was almost perfect. These measurements are therefore reliable, and can be used to investigate fetal brain development. Thalamic measurements are not reliable enough.

Enlarged Cavum Septi Pellucidi and Vergae in the Fetus: A Cause for Concern

OBJECTIVES

To investigate fetal cases identified at our institution to determine whether an enlarged cavum septi pellucidi or cavum vergae is associated with other fetal abnormalities and whether its presence warrants more detailed investigation of the fetus.

METHODS

In a retrospective study, 15 high- and low-risk patients undergoing prenatal sonography who had an enlarged cavum septi pellucidi or cavum vergae identified were reviewed. Data were collected for the sonographic study indication, gestation age at diagnosis of a prominent cavum, and associated anomalies. Follow-up outcome data regarding further imaging, karyotype, diagnosis of brain anomaly, and associated congenital abnormalities were obtained.

RESULTS

Fifteen patients met the inclusion criteria. Nine patients were identified as having a prominent cavum septi pellucidi, and 6 were identified as having a prominent cavum vergae. The mean gestational age ± SD was 22.7 ± 5.9 weeks. Eleven patients made it to delivery. Of the 15 patients, 4 were thought to have trisomy 21, and 13 had congenital anomalies. Outcomes included 10 major adverse outcomes, 4 cases with normal development or minor abnormalities, and 1 lost to follow-up. An isolated dilated cavum on prenatal sonography was seen in 5 cases: 1 with lissencephaly on a neonatal examination, 3 premature deliveries (1 demise, 1 hospice, and 1 normal), and 1 unknown.

CONCLUSIONS

Our cohort had many associated clinical anomalies: 3 confirmed trisomy 21 and 1 probable trisomy 21, 2 genetic disorders, and 10 major adverse outcomes, 5 of which were grave. Although we studied a small cohort, we conclude that an enlarged cavum septi pellucidi or cavum vergae warrants consideration of genetic counseling, which may include noninvasive prenatal testing (cell-free DNA), amniocentesis with microarray testing, or both.

5D CNS+ Software for Automatically Imaging Axial, Sagittal, and Coronal Planes of Normal and Abnormal Second-Trimester Fetal Brains

The purpose of this study was to test new 5D CNS+ software (Samsung Medison Co, Ltd, Seoul, Korea), which is designed to image axial, sagittal, and coronal planes of the fetal brain from volumes obtained by 3-dimensional sonography. The study consisted of 2 different steps. First in a prospective study, 3-dimensional fetal brain volumes were acquired in 183 normal consecutive singleton pregnancies undergoing routine sonographic examinations at 18 to 24 weeks' gestation. The 5D CNS+ software was applied, and the percentage of adequate visualization of brain diagnostic planes was evaluated by 2 independent observers. In the second step, the software was also tested in 22 fetuses with cerebral anomalies. In 180 of 183 fetuses (98.4%), 5D CNS+ successfully reconstructed all of the diagnostic planes. Using the software on healthy fetuses, the observers acknowledged the presence of diagnostic images with visualization rates ranging from 97.7% to 99.4% for axial planes, 94.4% to 97.7% for sagittal planes, and 92.2% to 97.2% for coronal planes. The Cohen κ coefficient was analyzed to evaluate the agreement rates between the observers and resulted in values of 0.96 or greater for axial planes, 0.90 or greater for sagittal planes, and 0.89 or greater for coronal planes. All 22 fetuses with brain anomalies were identified among a series that also included healthy fetuses, and in 21 of the 22 cases, a correct diagnosis was made. 5D CNS+ was efficient in successfully imaging standard axial, sagittal, and coronal planes of the fetal brain. This approach may simplify the examination of the fetal central nervous system and reduce operator dependency.

Anatomic Eponyms in Neuroradiology: Brain, Cerebral Vasculature, and Calvarium

Medical eponyms are ubiquitous, numerous, and at times controversial. They are often useful for succinctly conveying complex concepts, and familiarity with eponyms is important for proper usage and appropriate communication. In this historical review, we identify 18 anatomic eponyms used to describe structures of the brain, cerebral vasculature, and calvarium. For each structure, we first offer a biographical sketch of the individual for whom the structure is named. This is followed by a description of the anatomic structure and a brief discussion of its clinical relevance.

Role of 3-D ultrasound in clinical obstetric practice: evolution over 20 years

The use of 3-D ultrasound in obstetrics has undergone dramatic development over the past 20 years. Since the first publications on this application in clinical practice, several 3-D ultrasound techniques and rendering modes have been proposed and applied to the study of fetal brain, face and cardiac anatomy. In addition, 3-D ultrasound has improved calculations of the volume of fetal organs and limbs and estimations of fetal birth weight. And furthermore, angiographic patterns of fetal organs and the placenta have been assessed using 3-D power Doppler ultrasound quantification. In this review, we aim to summarize current evidence on the clinical relevance of these methodologies and their application in obstetric practice.

Reference charts for fetal corpus callosum length: a prospective cross-sectional study of 2950 fetuses

OBJECTIVES

The purpose of this study was to establish reference charts for fetal corpus callosum length in a convenience sample.

METHODS

A prospective cross-sectional study was conducted at the Artemisia Fetal-Maternal Medical Center between December 2008 and January 2012. Among 16,975 fetal biometric measurements between 19 weeks and 37 weeks 6 days' gestation, 3438 measurements of the corpus callosum (20.3%) were available. After excluding 488 measurements (14.2%), a total of 2950 fetuses (85.8%) were considered and analyzed only once. Parametric and nonparametric quantile regression models were used for the statistical analysis. To evaluate the robustness of the proposed reference charts with respect to various distributional assumptions on the sonographic measurements at hand, we compared the gestational age (GA)-specific reference curves produced by the statistical methods used.

RESULTS

The mean corpus callosum length was 26.18 mm (SD, 4.5 mm; 95% confidence interval, 26.01-26.34 mm). The linear regression equation expressing the length of the corpus callosum as a function of GA was length (mm) = -11.17 + 1.62 × GA. The correlation between the dimension and gestation was expressed by the coefficient r = 0.83. Normal mean lengths according the parametric and nonparametric methods were defined for each week of gestation.

CONCLUSIONS

This work provides new quantile-based reference charts for corpus callosum length measurements that may be useful for diagnosis of congenital corpus callosum anomalies in fetal life.

Second trimester fetal neurosonography: reconstructing cerebral midline anatomy and anomalies using a novel three-dimensional ultrasound technique

OBJECTIVE

To describe the application of a novel 3D ultrasound reconstructing technique (OMNIVIEW) that may facilitate the evaluation of cerebral midline structures at the second trimester anatomy scan.

METHODS

Fetal cerebral midline structures from 300 consecutive normal low-risk pregnant women were studied prospectively by 2D and 3D ultrasound between 19-23 weeks of gestation. All the newborn infants underwent pediatric follow-up and were considered normal up to 2 years of life. In addition, five confirmed pathologic cases were evaluated and the abnormal features using this technique are described in this clinical series.

RESULTS

Off-line volume data sets displaying the corpus callosum and the cerebellar vermis anatomy were accurately reconstructed in 98.5% and 96% of cases from sagittal and axial planes, respectively. For pathological cases, an agreement rate of 0.96 and 0.91 for midsagittal and axial planes, respectively, was observed.

CONCLUSIONS

This study demonstrates the feasibility of including 3D ultrasound as an adjunct technique for the evaluation of cerebral midline structures in the second trimester fetus. Future prospective studies will be necessary to evaluate if the application of this novel 3D reconstructing technique as a step forward following 2D second trimester screening scan will improve the prenatal detection of cerebral midline anomalies in the low-risk pregnant population.

Biometry of the fetal corpus callosum by three-dimensional ultrasound

OBJECTIVES

To construct reference ranges of quantitative characteristics of the fetal corpus callosum.

METHODS

Women referred to a tertiary center for sonographic examination were recruited to undergo a detailed fetal scan from 17 to 41 weeks of gestation. Three-dimensional (3D) sonographic volumes of normal fetal brains were acquired and analyzed offline. We obtained three different measurements of the corpus callosal length, as well as the height (/thickness) of its segments, namely the rostrum, genu, body and splenium.

RESULTS

Initially we recruited 604 pregnant women, of whom 138 were excluded because of various disorders/abnormalities, multiple pregnancy or gestational age < 18 weeks. Thus, included in the analysis were 466 sonographic volumes of normal fetal brains from singleton pregnancies, acquired by transabdominal ( n = 170) or transvaginal (n = 296) ultrasound. The corpus callosum was visualized as a hypoechoic structure. Reference ranges were established for the following parameters: curved corpus callosal length, inner-inner corpus callosal length, outer-outer corpus callosal length, rostrum height, genu height, body height and splenium height. We observed non-linear growth and an approximately four-fold increase in all corpus callosal lengths, a three-fold increase in rostrum height, a four-fold increase in genu height, a two-fold increase in body height and a three-fold increase in splenium height between 18 and 41 weeks. The growth patterns of rostrum and body height appeared to be similar: there was rapid development until 24 and 22 weeks of gestation, respectively, and growth slowed beyond this period. The growth patterns of genu and splenium were also similar, being characterized by progressive growth throughout gestation.

CONCLUSIONS

Using 3D ultrasound, we have constructed reference charts for measurements of the corpus callosum. Knowledge of the normal growth pattern may be useful for evaluation of abnormal development of the corpus callosum, and so help in the accurate diagnosis of pathologies such as hypogenesis and dysgenesis.

Sonographic appearance of the cavum septum pellucidum et vergae in normal fetuses in the second and third trimesters of pregnancy

BACKGROUND

To characterize the cavum septum pellucidum et vergae (CSPV) in normal fetuses in the second to third trimester.

METHODS

The cavum septum pellucidum (CSP) and CSPV were investigated in 322 uncomplicated singleton pregnancies from 25 to 39 weeks' gestation. Visualization rate, width, and morphology of both CSP and cavum vergae (CV) were assessed by ultrasound and MRI.

RESULTS

The CSP and CSPV visualization rates were 100% and 7.8% (25/322), respectively. The mean widths were 6.3 ± 1.2 mm (3.4-10 mm) and 6.7 ± 1.0 mm (5.1-9 mm), respectively, with no significant correlation between width and gestational age (r = -0.108, p > 0.05 and r = -0.182, p > 0.05, respectively). In CSPV fetuses, the CV to CSP ratio was 1.004 ± 0.018 (0.967-1.033). All CSPVs were rectangular in the transverse plane and extended posteriorly beyond the midpoint of the brain.

CONCLUSIONS

Common features of CSPVs include (1) a rectangular morphology, (2) communication between the two cavities, (3) a CV width within the normal range for CSP, and (4) a CV-CSP ratio of 1. These findings may help distinguish normal from abnormal CSPV.

Fetal MRI: the sonographer's view

Fetal magnetic resonance imaging (MRI) is used with increasing frequency as a complementary imaging modality to ultrasound (US) in prenatal diagnosis. Fetal MRI displays the fetal, uterine, and extrauterine anatomy in ways that allow confirmation of normal anatomy and the diagnosis of pathological entities that were formerly very difficult to detect prenatally. Comparison of US views with standard orthogonal plane MR images reinforces the understanding of fetal anatomy as visualized with US. Technological advances in US equipment have allowed the recent description of subtle fetal anatomical structures. Similarly, knowledge of the MRI appearances of pathological conditions has opened opportunities for the sonographic diagnosis of entities such as brainstem malformations and alterations in the normal transient laminar pattern that occur during development of the fetal cerebrum. Fetal MRI can confirm suspicious US findings and thus add confidence in a particular prenatal diagnosis before performing invasive and interventional procedures. Specific MRI sequences can be used to add information about the chemical composition of fetal structures, such as fat, blood, and meconium. Dynamic MRI sequences have increased understanding of gestational age-dependent behavior, and assist the sonographer in assessment of fetal structural anomalies that cause abnormal movement and behavior. The technological ability of US to demonstrate very small structures complements the lower resolution of fetal MR images, whereas the ability of MR to visualize the whole fetus improves the limited views necessitated by US. Therefore, both US and fetal MRI have complementary strengths and weaknesses that can be used to full advantage in prenatal diagnosis.

Quantitative evaluation of the fetal cerebellar vermis using the median view on three-dimensional ultrasound

OBJECTIVE

The purpose of this study was to investigate the effectiveness for quantitative evaluation of cerebellar vermis using three-dimensional (3D) ultrasound and to establish a nomogram for Chinese fetal vermis measurements during gestation.

METHODS

Sonographic examinations were performed in normal fetuses and in cases suspected of the diagnosis of vermian rotation. 3D median planes were obtained with both OMNIVIEW and tomographic ultrasound imaging.

RESULTS

Measurements of the cerebellar vermis were highly correlated between two-dimensional and 3D median planes. The diameter of the cerebellar vermis follows growth approximately predicted by the quadratic regression equation. The normal vermis was almost parallel to the brain stem, with the average angle degree to be <2° in normal fetuses. The average angle degree of the 9 cases of vermian rotation was >5°.

CONCLUSIONS

Three-dimensional median planes are obtained more easily than two-dimensional ones, and allow accurate measurements of the cerebellar vermis. The 3D approach may enable rapid assessment of fetal cerebral anatomy in standard examination. Measurements of cerebellar vermis may provide a quantitative index for prenatal diagnosis of posterior fossa malformations.

[Prenatal analysis of primary sulci by ultrasonography and MRI]

Gyration abnormalities often reflect severe neurological diseases. Their diagnosis is impeded by our limited knowledge about normal sulci anatomy throughout fetal brain development. Primary sulci appears in a specific chronology which is unchanged among all fetuses. We think it is interesting to remind of sulci anatomy and then to depict sulci MRI and ultrasonography appearance at 22, 27 and 32 weeks of gestation. We pay particular attention to the lateral sulcus, also called Sylvian fissure.

Prenatal neurologic anomalies: sonographic diagnosis and treatment

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

Reference values for the length and area of the fetal corpus callosum on 3-dimensional sonography using the transfrontal view

OBJECTIVES

The purpose of this study was to determine reference values for the length and area of the fetal corpus callosum between 20 and 33 weeks' gestation using 3-dimensional sonography.

METHODS

A cross-sectional study was performed in 293 healthy pregnant women between 20 and 33 weeks' gestation. The length and area of the corpus callosum were obtained via the transfontal view with the metopic suture as an acoustic window using 3-dimensional sonographic aquisitions. Linear and weighted polynomial regression models were used, which were adjusted by residual analysis and the R(2) determination coefficient. Intraobserver and interobserver reproducibilities were analyzed by an intraclass correlation coefficient.

RESULTS

The mean corpus callosum length ± SD varied from 19.52 ± 2.24 to 40.36 ± 2.87 mm, whereas the mean area varied from 0.44 ± 0.11 to 1.47 ± 0.21 cm(2) at 20 and 33 weeks, respectively. The length and area were highly correlated with gestational age: corpus callosum length = -52.41 + 4.71 × gestational age - 0.06 × gestational age(2) (R(2) = 0.868); and corpus callosum area = -2.47 + 0.16 × gestational age - 0.000037 × gestational age(2) (R(2) = 0.765). The intraobserver and interobserver reproducibilities were excellent, with intraclass correlation coefficients of 0.98 and 0.94 for the length and 0.99 and 0.90 for the area, respectively.

CONCLUSIONS

Reference values for the length and the area of the fetal corpus callosum between 20 and 33 weeks' gestation were determined with high reproducibility.

An algorithm based on OmniView technology to reconstruct sagittal and coronal planes of the fetal brain from volume datasets acquired by three-dimensional ultrasound

OBJECTIVE

To describe a novel algorithm, based on the new display technology 'OmniView', developed to visualize diagnostic sagittal and coronal planes of the fetal brain from volumes obtained by three-dimensional (3D) ultrasonography.

METHODS

We developed an algorithm to image standard neurosonographic planes by drawing dissecting lines through the axial transventricular view of 3D volume datasets acquired transabdominally. The algorithm was tested on 106 normal fetuses at 18-24 weeks of gestation and the visualization rates of brain diagnostic planes were evaluated by two independent reviewers. The algorithm was also applied to nine cases with proven brain defects.

RESULTS

The two reviewers, using the algorithm on normal fetuses, found satisfactory images with visualization rates ranging between 71.7% and 96.2% for sagittal planes and between 76.4% and 90.6% for coronal planes. The agreement rate between the two reviewers, as expressed by Cohen's kappa coefficient, was > 0.93 for sagittal planes and > 0.89 for coronal planes. All nine abnormal volumes were identified by a single observer from among a series including normal brains, and eight of these nine cases were diagnosed correctly.

CONCLUSIONS

This novel algorithm can be used to visualize standard sagittal and coronal planes in the fetal brain. This approach may simplify the examination of the fetal brain and reduce dependency of success on operator skill.

Satisfactory rate of post-processing visualization of fetal cerebral axial, sagittal, and coronal planes from three-dimensional volumes acquired in routine second trimester ultrasound practice by sonographers of peripheral centers

OBJECTIVE

The aim of this study was to evaluate the feasibility to visualize central nervous system (CNS) diagnostic planes from three-dimensional (3D) brain volumes obtained in ultrasound facilities with no specific experience in fetal neurosonography.

METHODS

Five sonographers prospectively recorded transabdominal 3D CNS volumes starting from an axial approach on 500 consecutive pregnancies at 19-24 weeks of gestation undergoing routine ultrasound examination. Volumes were sent to the referral center (Department of Obstetrics and Gynecology, Università Roma Tor Vergata, Italy) and two independent reviewers with experience in 3D ultrasound assessed their quality in the display of axial, coronal, and sagittal planes.

RESULTS

CNS volumes were acquired in 491/500 pregnancies (98.2%). The two reviewers acknowledged the presence of satisfactory images with a visualization rate ranging respectively between 95.1% and 97.14% for axial planes, 73.72% and 87.16% for coronal planes, and 78.41% and 94.29% for sagittal planes. The agreement rate between the two reviewers as expressed by Cohen's kappa coefficient was >0.87 for axial planes, >0.89 for coronal planes, and >0.94 for sagittal planes. The presence of a maternal body mass index >30 alters the probability of achieving satisfactory CNS views, while existence of previous maternal lower abdomen surgery does not affect the quality of the reconstructed planes.

CONCLUSIONS

CNS volumes acquired by 3D ultrasonography in peripheral centers showed a quality high enough to allow a detailed fetal neurosonogram.

Evaluation of offline analysis of archived three-dimensional volume datasets in the diagnosis of fetal brain abnormalities

OBJECTIVE

To retrospectively evaluate the reliability of offline manipulation of archived three-dimensional (3D) ultrasound volumes in the assessment of the normal fetal brain and the diagnosis of fetal brain abnormalities.

METHODS

Seventy-nine 3D volume datasets, archived at the time of scanning, from women attending a tertiary center, were analyzed. They comprised 52 cases with brain abnormalities and 27 normal controls. Postnatal magnetic resonance imaging or postmortem examination confirmed the final diagnosis in all cases with brain anomalies. Offline analysis of the 79 anonymized 3D volume datasets was carried out by three fetal medicine experts, examiner one (E1), examiner two (E2) and examiner three (E3), using 4D View software. The experts were blinded to any prior diagnosis or history. Data were collected on a specially designed data sheet and entered into a specialized database for analysis. Results were compared between examiners, with the initial two-dimensional (2D) diagnosis and with the final definitive diagnosis by calculation of percentage agreement and kappa coefficients.

RESULTS

Of the 52 cases with brain anomalies, the correct diagnosis was reached in 88.5% (46/52), 98.1% (51/52) and 92.3% (48/52) of cases on analysis of the 3D volumes by E1, E2 and E3, respectively, whereas only 82.7% (43/52) of cases were correctly diagnosed on the initial 2D examination when compared with the definitive diagnosis. Fetuses without brain anomalies were identified as such by the three experts with 100% agreement. There was good agreement between the initial 2D examination and the analysis of 3D volumes by each of the experts: 86.1% for E1 (κ = 0.7), 89.9% for E2 (κ = 0.79) and 88.6% for E3 (κ = 0.76).

CONCLUSIONS

3D volume datasets are an appropriate and reliable format for storing data from examination of the fetal brain. Offline analysis of 3D datasets is a reliable method that can be used to help in the assessment of brain anomalies and could be a useful adjunct to realtime 2D ultrasonography.

Collaborative study on 3-dimensional sonography for the prenatal diagnosis of central nervous system defects

OBJECTIVES

Prenatal diagnosis of central nervous system (CNS) anomalies by 2-dimensional sonography is challenging because of difficulties in obtaining complete visualization of the fetal brain during routine examinations, which is necessary for identification of its axial, coronal, and sagittal planes. Three-dimensional (3D) sonography has been introduced as a tool for studying the fetal CNS because of its ability to facilitate examinations of the fetal brain. The objective of this study was to determine inter-center agreement in diagnosing CNS defects by review of 3D volume data sets.

METHODS

This study included 11 centers with expertise in 3D fetal neurosonography. A total of 217 fetuses with and without confirmed CNS defects were scanned after 18 weeks' gestation, and their volume data sets were uploaded onto a centralized file transfer protocol server and later analyzed by all of the centers. Intercenter agreement was determined using a κ statistic for multiple raters.

RESULTS

All volumes were made anonymous and sent to the centers for blinded analysis with the exception of the data sets they had themselves previously uploaded. For identification of fetuses with CNS defects, the sensitivity, specificity, positive and negative predictive values, and false-positive and -negative rates were 93.3%, 96.5%, 96.5%, 93.3%, 3.5%, and 6.7%, respectively. No differences were found in the efficacy of the diagnostic indices according to either the route of acquisition (transabdominal or trans-vaginal) or the gestational age at diagnosis (18-24 or >24 weeks). Intercenter agreement was excellent (κ = 0.92; 95% confidence interval, 0.88-0.97).

CONCLUSIONS

Among centers with technical expertise, remote review of 3D sonographic volumes of the fetal CNS resulted in an accurate and reliable method for diagnosis of fetal brain malformations.

Assessment of corpus callosum biometric measurements at 18 to 32 weeks' gestation by 3-dimensional sonography

OBJECTIVES

The purposes of this study were to construct reference limits for corpus callosum dimensions measured on images reconstructed from 3-dimensional (3D) sonography and to evaluate the reproducibility of these measurements.

METHODS

Three-dimensional sonographic volumes were acquired transabdominally from an axial view of the head in 361 fetuses cross-sectionally studied at 18 to 32 weeks' gestation. Offline analysis of the fetal brain midsagittal plane was used to evaluate the length and area of the corpus callosum and corpus callosum-cavum septi pellucidi complex. The agreement between 2-dimensional (2D) and 3D measurements as well as the interobserver variability in 3D measurements were assessed by interclass correlation coefficients (ICCs).

RESULTS

Adequate visualization of the midsagittal plane was obtained in 98.1% of the fetuses. A clear distinction between the corpus callosum and cavum septi pellucidi was obtained in 35.7% of the fetuses, whereas in the remaining cases, the corpus callosum-cavum septi pellucidi complex was visualized as a single echogenic structure. The corpus callosum-cavum septi pellucidi complex length (r = 0.806; P < .0001), corpus callosum-cavum septi pellucidi complex area (r = 0.920; P < .0001), and corpus callosum area (r = 0.713; P < .0001) showed a significant linear growth with gestation. A good agreement was found between measurements from both 2D and 3D sonographic views (corpus callosum length ICC, 0.916) as well as between measurements obtained by different observers (corpus callosum-cavum septi pellucidi complex length ICC, 0.936; corpus callosum-cavum septi pellucidi complex area ICC, 0.931).

CONCLUSIONS

Measurements of the corpus callosum and cavum septi pellucidi can be obtained from the midsagittal plane of the fetal brain reconstructed from 3D volumes acquired transabdominally. The constructed nomograms may facilitate the diagnosis of corpus callosum abnormalities.

Depth of brain fissures in normal fetuses by prenatal ultrasound between 19 and 30 weeks of gestation

OBJECTIVE

To establish normal reference ranges for the depth of the insula and Sylvian (SF), parieto-occipital (POF) and calcarine (CF) fissures on prenatal ultrasound between 19 and 30 weeks of gestation.

METHODS

This was a prospective study of 15 consecutive normal fetuses per gestational week between 19 + 0 and 30 + 6 weeks. We measured the depth of the insula and SF in a standard transventricular axial plane of the fetal head; the depth of the POF in a plane above and parallel to that used for the insula; and the depth of the CF in a coronal view of the posterior fossa. All measurements were done transabdominally during the routine second- or third-trimester examination. Reproducibility for each of the parameters was assessed by two operators using stored images from 30 cases.

RESULTS

The depth of the four structures increased with increasing gestational age. The insula and SF could be seen in all cases from 19 weeks onwards, while the POF and CF could be identified in 93.3% and 6.6% of cases, respectively, at 19 weeks. From 20 weeks onwards, the POF could be seen in all examinations, as could the CF from 24 weeks. Intra- and interobserver reproducibility analysis showed good results.

CONCLUSIONS

Assessment of the insula, SF, POF and CF is feasible during prenatal ultrasound examination using standard views of the fetal head. Since the normal ranges increase with gestational age, they could be used to estimate brain development. It is possible that this assessment might be incorporated into the neurosonogram to identify fetuses at risk of maturation disorders or as a complement to other standard evaluations.

Our clinical experience about prenatal diagnosis and neonatal outcomes of fetal central nervous system anomalies

OBJECTIVE

To present a retrospective analysis of the prenatal diagnosis and the outcome of fetuses diagnosed with central nervous system (CNS) anomalies.

MATERIALS AND METHODS

We reviewed the medical records and ultrasound data of 69 cases diagnosed with CNS anomalies from 2007 to 2008. We described the prenatal diagnosis, associated findings, and outcome of these patients.

RESULTS

Sixty-nine patients were diagnosed with CNS anomalies. Of these, 31 had ventriculomegaly + hydrocephaly, 14 had spina bifida + meningomyelosel, 5 had choroid plexus cyst, 5 had Dandy Walker malformation, 3 had sacrocoxigeal teratoma, 2 had encephalosel, 1 had microcephaly, and 1 had Arnold Chiari malformation. Eight amniocentesis, three cord blood sampling, and two fetal reduction procedure were performed. Nine pregnancy termination and 36 delivery were performed. Neurosurgical correction was performed for neonates with spina bifida, hydrocephaly and sacrocoxigeal teratoma. Twenty-one neonates were discharged with cure, 4 neonates with follow-up, 7 neonates with paraplegia, and 13 neonates died.

CONCLUSION

The outcome of fetuses with CNS anomalies was shown to depend mainly on the degree of neural tube defect and the associated anomalies were the most important factors in surviving.

Basic as well as detailed neurosonograms can be performed by offline analysis of three-dimensional fetal brain volumes

OBJECTIVES

To evaluate the feasibility and the processing time of offline analysis of three-dimensional (3D) brain volumes to perform a basic, as well as a detailed, targeted, fetal neurosonogram.

METHODS

3D fetal brain volumes were obtained in 103 consecutive healthy fetuses that underwent routine anatomical survey at 20-23 postmenstrual weeks. Transabdominal gray-scale and power Doppler volumes of the fetal brain were acquired by one of three experienced sonographers (an average of seven volumes per fetus). Acquisition was first attempted in the sagittal and coronal planes. When the fetal position did not enable easy and rapid access to these planes, axial acquisition at the level of the biparietal diameter was performed. Offline analysis of each volume was performed by two of the authors in a blinded manner. A systematic technique of 'volume manipulation' was used to identify a list of 25 brain dimensions/structures comprising a complete basic evaluation, intracranial biometry and a detailed targeted fetal neurosonogram. The feasibility and reproducibility of obtaining diagnostic-quality images of the different structures was evaluated, and processing times were recorded, by the two examiners.

RESULTS

Diagnostic-quality visualization was feasible in all of the 25 structures, with an excellent visualization rate (85-100%) reported in 18 structures, a good visualization rate (69-97%) reported in five structures and a low visualization rate (38-54%) reported in two structures, by the two examiners. An average of 4.3 and 5.4 volumes were used to complete the examination by the two examiners, with a mean processing time of 7.2 and 8.8 minutes, respectively. The overall agreement rate for diagnostic visualization of the different brain structures between the two examiners was 89.9%, with a kappa coefficient of 0.5 (P < 0.001).

CONCLUSIONS

In experienced hands, offline analysis of 3D brain volumes is a reproducible modality that can identify all structures necessary to complete both a basic and a detailed second-trimester fetal neurosonogram.

Three-dimensional ultrasound imaging

This review is about the development of three-dimensional (3D) ultrasonic medical imaging, how it works, and where its future lies. It assumes knowledge of two-dimensional (2D) ultrasound, which is covered elsewhere in this issue. The three main ways in which 3D ultrasound may be acquired are described: the mechanically swept 3D probe, the 2D transducer array that can acquire intrinsically 3D data, and the freehand 3D ultrasound. This provides an appreciation of the constraints implicit in each of these approaches together with their strengths and weaknesses. Then some of the techniques that are used for processing the 3D data and the way this can lead to information of clinical value are discussed. A table is provided to show the range of clinical applications reported in the literature. Finally, the discussion relating to the technology and its clinical applications to explain why 3D ultrasound has been relatively slow to be adopted in routine clinics is drawn together and the issues that will govern its development in the future explored.

A systematic technique using 3-dimensional ultrasound provides a simple and reproducible mode to evaluate the corpus callosum

OBJECTIVE

The aim of this study was to evaluate a rapid 3-dimensional ultrasound-assisted technique for evaluation of the corpus callosum as an integral part of the anatomic survey.

STUDY DESIGN

Transabdominal 3-dimensioal gray scale and power Doppler volumes of the fetal brain were acquired in 102 consecutive healthy fetuses at 20-23 postmenstrual weeks. Offline analysis was performed by 2 of the authors using a systematic approach of "volume manipulation." Diagnostic-quality visualization of the corpus callosum and the pericallosal arteries on the median plane was recorded by the 2 examiners independently.

RESULTS

The median plane was easily obtained in all cases. Diagnostic-quality images of the corpus callosum were recorded in 93.1% and 99.0% and of the pericallosal arteries in 94.4% and 95.5% of the cases, by the 2 examiners, respectively.

CONCLUSION

Three-dimensional ultrasound enables a rapid and easy evaluation of the corpus callosum that may facilitate its inclusion as an integral part of the routine anatomic survey.

Interobserver reproducibility of transabdominal 3-dimensional sonography of the fetal brain

OBJECTIVE

The purpose of this study was to assess the interobserver reproducibility of transabdominal 3-dimensional (3D) fetal neurosonography.

METHODS

This was a prospective observational study. We studied 23 consecutive singleton pregnancies between 18 and 23 weeks' gestation. All cases had normal fetal neurosonographic examination findings, which were confirmed after birth. A 3D sonographic volume of the fetal head was acquired transabdominally by a single operator using an axial approach. Fetal brain anatomy was later analyzed offline by 2 different operators. Axial, sagittal, and coronal views of the fetal brain were obtained to perform a detailed evaluation of the fetal brain. Each operator defined the scanning planes obtained as adequate or inadequate. Results were evaluated with 2 x 2 tables and the Cohen kappa coefficient to assess interobserver agreement.

RESULTS

Good-quality multiplanar images were obtained in 23 of 23 cases. The rate of adequate visualization was 100% for all of the axial planes, with kappa values of 1.00. For sagittal and coronal planes, the rate of visualization ranged between 78% and 91%, with kappa values ranging between 0.61 and 0.83.

CONCLUSIONS

Transabdominal 3D sonography of the fetal brain at 18 to 23 weeks' gestation has an acceptable degree of interobserver reproducibility.

Prenatal diagnosis of posterior fossa anomalies--an overview

Ultrasonography of the central nervous system is an integral part of a prenatal scan, and the development of imaging technologies has led to better diagnostic possibilities. Posterior fossa anomalies have traditionally been divided into Dandy Walke malformation, Dandy Walker variation and megacisterna magna, but this approach, due to diversity of the extensive number of possible disorders covered by this classification, unables accurate prognosis and therefore adequate counselling. An alternative approach to the classification of posterior fossa anomalies is to divide them into agenesis of the vermis, which could be partial or complete, cerebellar hypoplasia, pontocerebellar hypoplasia and cerebellar atrophy. Different ultrasonographic and magnetic resonance imagining of appearances of the posterior fossa anomalies in prenatal period are discussed in the article, as well as possible syndromes and prognosis of different entities. Diversity of anomalies of the central nervous system, and in particular, subtle differences in prenatal appearances of posterior fossa anomalies, which may have major impact on the prognosis, demand a multidisciplinary approach that encompasses two-dimensional and three-dimensional ultrasound scan, magnetic resonance imaging, infectious diseases and metabolic disorders work-ups as well as individual approach to every case involving of a team of experts in the field of perinatology, radiology, paediatrics, neurology and genetics.

Three-dimensional ultrasonography of the fetal vermis at 18 to 26 weeks' gestation: time of appearance of the primary fissure

OBJECTIVE

The purpose of this study was to establish the normality of the fetal vermis, ie, the time of appearance of the primary fissure, as well as its measurements between 18 and 26 weeks' gestation, using 3-dimensional (3D) ultrasonography.

METHODS

A prospective cross-sectional study of normal singleton pregnancies was conducted. Examinations were performed with high-resolution transabdominal ultrasonography using the axial plane in 173 fetuses between 18 and 26 weeks' gestation. Postprocessing measurements of the fetal vermis were done with 4-dimensional software using static volume contrast imaging and tomographic ultrasound imaging in the C-plane. Detection of the primary fissure was evaluated in all cases, and the time of appearance was documented.

RESULTS

Adequate vermis measurements were obtained in 173 fetuses. Vermian length as a function of gestational age was expressed by regression equations, and the correlation coefficients were found to be highly statistically significant (P < .001). The normal mean +/- 2 SD for each gestational week was defined. The primary fissure was observed at 24 weeks' gestation in all cases, at 22 weeks in 94% of cases, and as early as 18 weeks in 40%.

CONCLUSIONS

This 3D study documents the appearance of the primary fissure and presents the normal range of vermian measurements, confirming normal development of the fetal vermis starting as early as 18 weeks' gestation. It also shows an easy method for visualizing the vermis with 3D ultrasonography at every gestational week regardless of fetal presentation.

Three-dimensional sonographic evaluations of embryonic brain development

OBJECTIVE

The purpose of this presentation is to show 3-dimensional development of the ventricles of the brain in early pregnancy, from 6 to 13 weeks, and to provide a reference for early diagnosis of central nervous system anomalies such as hydrocephalus and holoprosencephaly.

METHODS

From March 2007 to August 2007, 46 patients were included. All patients had routine first-trimester 2- and 3-dimensional sonographic examinations at the same time. All cases were examined with a Voluson 730 Expert or Voluson E8 ultrasound scanner (GE Healthcare, Milwaukee, WI) using a 4- to 8- or 6- to 12-MHz transvaginal probe. Volumes were reviewed and analyzed with GE 4DView release 6 software. After the inversion-rendering mode was selected, volumes were dissected by the MagicCut function to show the ventricles.

RESULTS

A total of 34 volumes from 7 to 12 complete gestational weeks were successfully dissected. Those before 7 and after 12 weeks could not be dissected properly. The crown-rump length ranged from 12.7 to 68 mm. Twelve representative images of the rendered volumes in chronologic order are shown. The brain volume dissections of 2 fetuses with ventriculomegaly and alobar holoprosencephaly are shown for comparison.

CONCLUSIONS

Early human brain ventricular structures could be evaluated in vivo with 3-dimensional sonography. This presentation shows the timeline of brain development and provides reference images to compare possible anomalies of development.

Transfrontal three-dimensional visualization of midline cerebral structures

OBJECTIVE

To compare sonographic visualization of midline cerebral structures obtained by two-dimensional (2D) imaging and three-dimensional (3D) multiplanar and volume contrast imaging in the coronal plane (VCI-C), with transfrontal 3D acquisition.

METHODS

Sixty consecutive healthy fetuses in vertex presentation at a mean gestational age of 24 (range, 20-33) weeks underwent 2D and 3D ultrasound examination. Sagittal cerebral planes were reconstructed using 3D acquisition from axial planes by multiplanar analysis and by VCI-C. The reconstructed midline images of both these techniques were compared with the midline structures visualized directly in the A-plane by transfrontal 3D acquisition using a sweep angle of 30 degrees . Measurement of the corpus callosum and cerebellar vermis and visualization of the fourth ventricle and the main vermian fissures were compared. The sharpness of the images was also assessed qualitatively. Mid-sagittal tomographic ultrasound imaging (TUI) was also performed. 3D planes were compared with 2D transfontanelle median planes obtained by transabdominal or, when required, transvaginal sonography.

RESULTS

The midline plane could be obtained in 88% of multiplanar, 82% of VCI-C and 87% of transfrontal analyses. Measurements of the corpus callosum and cerebellar vermis obtained by 3D median planes were highly correlated. The clearest and sharpest definition of midline structures was obtained with transfrontal acquisition. Primary and secondary fissures of the cerebellar vermis could be detected in 13-26% of multiplanar, 18-35% of VCI-C and 52-79% of transfrontal analyses. 2D visualization was superior or equal to the 3D transfrontal approach in all the parameters compared.

CONCLUSION

3D planes obtained from axial acquisitions are simpler and easier to display than are transfrontal ones. However, artifacts and acoustic shadowing are frequent in 3D axial acquisition and spatial resolution is better in the direct visualization transfrontal technique. If the standard examination includes a view of the fetal facial profile, a quick 3D acquisition through the frontal sutures provides direct visualization for assessment of the midline structures. We believe that this volumetric methodology could represent a step towards incorporating a comprehensive fetal neuroscan into routine targeted organ evaluation.