The development of the fetal vermis: an in-utero sonographic evaluation

Reference Ranges for Vermis Biometry on Prenatal Ultrasound: Systematic Review and Meta-Analysis

PURPOSE

 To conduct a systematic review and meta-analysis of published nomograms for fetal vermis biometry.

MATERIALS AND METHODS

 A structured literature search was conducted to identify studies that reported normal measurements of the fetal vermis. A customized quality assessment tool was used to review the selected articles. Random effects meta-analysis was used to calculate normal ranges for vermian craniocaudal diameter, anteroposterior diameter, and surface area.

RESULTS

 A total of 21 studies were included for qualitative review and 3 studies were included for quantitative synthesis. The 3 included articles comprised a total of 10 910 measurements from gestational ages 17-35 weeks. The quality assessment demonstrated that there was generally poor reporting regarding maternal characteristics and neonatal outcomes. Except for one article with a large sample size, the mean number of fetuses per week of gestational age was 15.9, with the lowest number being 5. There was significant statistical heterogeneity. Non-visualization rates ranged from 0-35.4 %. The craniocaudal diameter (reported in 3 articles) increased from a mean of 7.90 mm (95 % confidence interval [CI] 7.42, 8.38) at 17 weeks to 21.90 mm (95 % CI 20.63, 23.16) at 35 weeks gestation. The anteroposterior diameter (reported in 2 articles) increased from 6.30 mm (95 % CI 5.42, 7.18) at 17 weeks to 15.85 (95 %CI 15.49, 16.21) at 32 weeks.

CONCLUSION

 Reference ranges for vermis biometry across gestation based on meta-analysis of existing references are provided. However, because many of the underlying studies suffered from significant methodological issues, the ranges should be used with caution.

Methodological quality of fetal brain structure charts for screening examination and targeted neurosonography: a systematic review

Introduction: The methodological quality of fetal brain charts has not been critically appraised yet. Material and methods: MEDLINE, EMBASE, CINAHL and the Web of Science databases were searched electronically up to December 31, 2020. The primary outcome was to evaluate the methodology of the studies assessing the growth of fetal brain structures throughout gestation. A list of 28 methodological quality criteria divided into three domains according to “study design”, “statistical and reporting methods”, and “specific relevant neurosonography aspects” was developed in order to assess the methodological appropriateness of the included studies. The overall quality score was defined as the sum of low risk of bias marks, with the range of possible scores being 0–28. This quality assessment was applied to each individual study reporting reference ranges for fetal brain structures. Results: Sixty studies were included in the systematic review. The overall mean quality score of the studies included in this review was 51.3%. When focusing on each of the assessed domains, the mean quality score was 53.7% for “study design”, 54.2% for “statistical and reporting methods” and 38.6% for “specific relevant neurosonography aspects”. The sample size calculation, the correlation with a postnatal imaging evaluation and the whole fetal brain assessment were the items at the highest risk of bias for each domain assessed, respectively. The subgroup analysis according to different anatomical location showed the lowest quality score for ventricular and periventricular structures and the highest for cortical structures. Conclusions: Most previously published studies reporting fetal brain charts suffers from poor methodology and are at high risk of biases, mostly when focusing on neurosonography issues. Further prospective longitudinal studies aiming at constructing specific growth charts for fetal brain structures should follow rigorous methodology to minimize the risk of biases, guarantee higher levels of reproducibility and improve the standard of care.

The Vermian-Crest Angle: A New Method to Assess Fetal Vermis Position within the Posterior Fossa Using 3-Dimensional Multiplanar Sonography

BACKGROUND

Normal morphometry of the vermis and its relation to the posterior fossa (PF) rule out most major anomalies of the cerebellum. However, accurate categorization of the position and size of the fetal vermis remains a challenge.

OBJECTIVE

Our aim was to test a new method to assess the position and size of fetal vermis on 3-dimensional ultrasound (3D-US).

METHODS

We measured the vermian-crest angle (VCA) in normal fetuses using multiplanar 3D-US. We also assessed the diameters (superoinferior, anteroposterior, and horizontal) and volume of the vermis. The Spearman rank test and linear and polynomial regression analyses were used for statistical purposes.

RESULTS

We included 126 fetuses. Mean ± SD gestational age (GA) was 26.3 ± 4.6 (range 17-35.5) weeks. Mean ± SD superoinferior, anteroposterior, and horizontal diameters were 16.2 ± 4.9, 11.2 ± 3.6, and 5.6 ± 1.6 mm, respectively. Median (range) vermian volume was 0.50 (0.05-2.9) cm3. The VCA was 64.49° ± 11.45. We found no correlation between GA and VCA (r = 0.15; p = 0.13), a linear correlation between GA and vermian diameters, and a quadratic correlation between GA and vermian volume.

CONCLUSIONS

We provide a new method to assess vermian position and size within the PF using 3D-US. The combined information may be of value for screening purposes, particularly to differentiate between the various pathological situations encountered within the PF.

Postnatal Brain Growth Assessed by Sequential Cranial Ultrasonography in Infants Born <30 Weeks' Gestational Age

BACKGROUND AND PURPOSE

Brain growth in the early postnatal period following preterm birth has not been well described. This study of infants born at <30 weeks' gestational age and without major brain injury aimed to accomplish the following: 1) assess the reproducibility of linear measures made from cranial ultrasonography, 2) evaluate brain growth using sequential cranial ultrasonography linear measures from birth to term-equivalent age, and 3) explore perinatal predictors of postnatal brain growth.

MATERIALS AND METHODS

Participants comprised 144 infants born at <30 weeks' gestational age at a single center between January 2011 and December 2013. Infants with major brain injury seen on cranial ultrasonography or congenital or chromosomal abnormalities were excluded. Brain tissue and fluid spaces were measured from cranial ultrasonography performed as part of routine clinical care. Brain growth was assessed in 3 time intervals: <7, 7-27, and >27 days' postnatal age. Data were analyzed using intraclass correlation coefficients and mixed-effects regression.

RESULTS

A total of 429 scans were assessed for 144 infants. Several linear measures showed excellent reproducibility. All measures of brain tissue increased with postnatal age, except for the biparietal diameter, which decreased within the first postnatal week and increased thereafter. Gestational age of ≥28 weeks at birth was associated with slower growth of the biparietal diameter and ventricular width compared with gestational age of <28 weeks. Postnatal corticosteroid administration was associated with slower growth of the corpus callosum length, transcerebellar diameter, and vermis height. Sepsis and necrotizing enterocolitis were associated with slower growth of the transcerebellar diameter.

CONCLUSIONS

Postnatal brain growth in infants born at <30 weeks' gestational age can be evaluated using sequential linear measures made from routine cranial ultrasonography and is associated with perinatal predictors of long-term development.

Measurement of normal fetal cerebellar vermis at 24-32 weeks of gestation by transabdominal ultrasound and magnetic resonance imaging: A prospective comparative study

OBJECTIVES

Fetal cerebellar vermis may be assessed by ultrasound (US) or magnetic resonance imaging (MRI), and median-plane views are best for evaluation. The purpose of this study was to compare measurements of normal fetal vermis at 24-32 weeks of gestation obtained in median plane by transabdominal 2D-US, 3D-US, and MRI.

METHODS

A prospective study was conducted, examining normal singleton fetuses between 24 and 32 weeks of gestation. Within a 24-h period, median-plane views of posterior fossa were generated using 2D-US, 3D-US, and MRI. Measurements of anteroposterior (AP) diameter, craniocaudal (CC) diameter, mid-sagittal surface area, brainstem-vermis (BV) angle and brainstem-tentorium (BT) angle were obtained to compare these imaging modalities.

RESULTS

A total of 180 fetuses were studied. Correlation among imaging methods was good, marked by the following intraclass correlation coefficients: AP diameter, 0.955; CC diameter, 0.956; mid-sagittal surface area, 0.982; BV angle, 0.810; and BT angle, 0.865 (p < 0.001).

CONCLUSIONS

Visualization rates of MRI, 3D-US, and transabdominal 2D-US were decremental, MRI being superior in this regard. However, these three imaging modalities correlated well in measuring cerebellar vermis and its surroundings.

Mathematical models of human cerebellar development in the fetal period

The evaluation of cerebellar growth in the fetal period forms a part of a widely used examination to identify any features of abnormalities in early stages of human development. It is well known that the development of anatomical structures, including the cerebellum, does not always follow a linear model of growth. The aim of the study was to analyse a variety of mathematical models of human cerebellar development in fetal life to determine their adequacy. The study comprised 101 fetuses (48 males and 53 females) between the 15th and 28th weeks of fetal life. The cerebellum was exposed and measurements of the vermis and hemispheres were performed, together with statistical analyses. The mathematical model parameters of fetal growth were assessed for crown-rump length (CRL) increases, transverse cerebellar diameter and ventrodorsal dimensions of the cerebellar vermis in the transverse plane, and rostrocaudal dimensions of the cerebellar vermis and hemispheres in the frontal plane. A variety of mathematical models were applied, including linear and non-linear functions. Taking into consideration the variance between models and measurements, as well as correlation parameters, the exponential and Gompertz models proved to be the most suitable for modelling cerebellar growth in the second and third trimesters of pregnancy. However, the linear model gave a satisfactory approximation of cerebellar growth, especially in older fetuses. The proposed models of fetal cerebellar growth constructed on the basis of anatomical examination and objective mathematical calculations could be useful in the estimation of fetal development.

Fetal Cerebellar Vermis Circumference Measured by 2-Dimensional Ultrasound Scan: Reference Range, Feasibility and Reproducibility

Purpose: To provide 2-dimensional ultrasonographic (2D-US) normograms of cerebellar vermis biometry, as well as to evaluate the feasibility and the reproducibility of these measurements in clinical practice. Materials and Methods: A prospective cross-sectional study of 328 normal singleton pregnancies between 18 and 33 weeks of gestation. Measurements of the fetal cerebellar vermis circumference (VC) in the mid-sagittal plane were performed by both a senior and a junior operator using 2D-US. VC as a function of gestational age (GA) was expressed by regression equations. In 24 fetuses 3-dimensional (3D) reconstructed planes were obtained in order to allow comparisons with 2D-US measurements. The agreement between 2D and 3D measurements and the interobserver variability were assessed by interclass correlation coefficients (ICC). Results: Satisfactory vermis measurements could be obtained in 89.9% of cases. The VC (constant= - 12.21; slope=2.447; r=0.887, p<0.0001) correlated linearly with GA. A high degree of consistency was observed between 2D and 3D ultrasound measurements (ICC=0.846 95% CI 679-0.930) as well as between measurements obtained by different examiners (ICC=0.890 95% CI 989-0.945). Conclusion: 2-dimensional ultrasonographic measurements of cerebellar vermis throughout gestation in the mid-sagittal view seem to be feasible and reproducible enough to be potentially used in clinical practice. Such measurements may supply a tool for accurate identification of posterior fossa anomalies, providing the basis for proper counseling and management and of these conditions.

Quantitative Evaluation of the Fetal Cerebellar Vermis Using the Median View on Two-Dimensional Ultrasound

Background

Evaluation of the cerebellum and vermis is one of the integral parts of the fetal cranial anomaly screening.

Objectives

The aim of this study was to create a nomogram for fetal vermis measurements between 17 and 30 gestational weeks.

Patients and Methods

This prospective study was conducted on 171 volunteer pregnant women between March 2013 and December 2014. Measurements of the fetal cerebellar vermis diameters in the sagittal plane were performed by two-dimensional transabdominal ultrasonography.

Results

Optimal median planes were obtained in 117 of the cases. Vermian diameters as a function of gestational age were expressed by regression equations and the correlation coefficients were found to be highly statistically significant (P < 0.001). The normal mean (± standard deviation) for each gestational week was also defined.

Conclusion

This study presents the normal range of the two-dimensional fetal vermian measurements between 17 and 30 gestational weeks. In the absence of a three-dimensional ultrasonography, two-dimensional ultrasonography could also be used confidently with more time and effort.

Reference Charts for Fetal Cerebellar Vermis Height: A Prospective Cross-Sectional Study of 10605 Fetuses

OBJECTIVE

To establish reference charts for fetal cerebellar vermis height in an unselected population.

METHODS

A prospective cross-sectional study between September 2009 and December 2014 was carried out at ALTAMEDICA Fetal-Maternal Medical Centre, Rome, Italy. Of 25203 fetal biometric measurements, 12167 (48%) measurements of the cerebellar vermis were available. After excluding 1562 (12.8%) measurements, a total of 10605 (87.2%) fetuses were considered and analyzed once only. Parametric and nonparametric quantile regression models were used for the statistical analysis. In order to evaluate the robustness of the proposed reference charts regarding various distributional assumptions on the ultrasound measurements at hand, we compared the gestational age-specific reference curves we produced through the statistical methods used. Normal mean height based on parametric and nonparametric methods were defined for each week of gestation and the regression equation expressing the height of the cerebellar vermis as a function of gestational age was calculated. Finally the correlation between dimension/gestation was measured.

RESULTS

The mean height of the cerebellar vermis was 12.7mm (SD, 1.6mm; 95% confidence interval, 12.7-12.8mm). The regression equation expressing the height of the CV as a function of the gestational age was: height (mm) = -4.85+0.78 x gestational age. The correlation between dimension/gestation was expressed by the coefficient r = 0.87.

CONCLUSION

This is the first prospective cross-sectional study on fetal cerebellar vermis biometry with such a large sample size reported in literature. It is a detailed statistical survey and contains new centile-based reference charts for fetal height of cerebellar vermis measurements.

Normal fetal posterior fossa in MR imaging: new biometric data and possible clinical significance

BACKGROUND AND PURPOSE

Posterior fossa malformations are a common finding in prenatal diagnosis. The objectives of this study are to re-evaluate existing normal MR imaging biometric data of the fetal posterior fossa, suggest and evaluate new parameters, and demonstrate the possible clinical applications of these data.

MATERIALS AND METHODS

This was a retrospective review of 215 fetal MR imaging examinations with normal findings and 5 examinations of fetuses with a suspected pathologic posterior fossa. Six previously reported parameters and 8 new parameters were measured. Three new parameter ratios were calculated. Interobserver agreement was calculated by using the intraclass correlation coefficient.

RESULTS

For measuring each structure, 151-211 MR imaging examinations were selected, resulting in a normal biometry curve according to gestational age for each parameter. Analysis of the ratio parameters showed that vermian lobe ratio and cerebellar hemisphere ratio remain constant with gestational age and that the vermis-to-cisterna magna ratio varies with gestational age. Measurements of the 5 pathologic fetuses are presented on the normal curves. Interobserver agreement was excellent, with the intraclass correlation coefficients of most parameters above 0.9 and only 2 parameters below 0.8.

CONCLUSIONS

The biometry curves derived from new and existing biometric data and presented in this study may expand and deepen the biometry we use today, while keeping it simple and repeatable. By applying these extensive biometric data on suspected abnormal cases, diagnoses may be confirmed, better classified, or completely altered.

Assessment of fetal midbrain and hindbrain in mid-sagittal cranial plane by three-dimensional multiplanar sonography. Part 1: comparison of new and established nomograms

OBJECTIVE

To construct nomograms for fetal midbrain (MB) and hindbrain (HB) dimensions, assessed in the mid-sagittal cranial plane by three-dimensional multiplanar sonographic reconstruction (3D-MPR).

METHODS

This was a prospective cross-sectional study of 334 healthy fetuses in low-risk singleton pregnancies between 16 and 35 gestational weeks. All sonographic volumes were obtained by sagittal acquisition. The following MB and HB parameters were evaluated in the mid-sagittal cranial plane using 3D-MPR: MB parameters tectal length (TL) and anteroposterior midbrain diameter (APMD), and HB parameters anteroposterior pons diameter (APPD), superoinferior vermian diameter (SIVD), anteroposterior vermian diameter (APVD) and anteroposterior diameter of the fourth ventricle (APDFV). The measurements were presented as growth charts according to gestational age.

RESULTS

MB and HB biometry were best assessed between 19 and 29 weeks. During this period, adequate visualization was achieved for successful measurement of TL in 90.9% of cases, APMD in 86.6%, APPD in 73.7%, SIVD in 74.2%, APVD in 71% and APDFV in 71%. There was a linear growth pattern, with Pearson correlation coefficients of 0.79 for TL, 0.88 for APMD, 0.91 for APPD, 0.95 for SIVD, 0.88 for APVD and 0.88 for APDFV (P < 0.0001 for each). The mean intra- and interobserver variations for the MB measurements and vermian diameters ranged between 4.3% and 9%. APPD and APDFV showed highest mean variations: 9.0% and 19.4% (intraobserver) and 11.6% and 17.7% (interobserver), respectively.

CONCLUSION

We present new nomograms for assessment of the fetal MB and HB using 3D-MPR in the mid-sagittal cranial plane. To our knowledge, these are the first proposed nomograms for fetal MB dimensions.

Quantitative evaluation of fetal brainstem-vermis and brainstem-tentorium angles by three-dimensional ultrasound

The aim of this study was to determine reference values and ranges for brainstem-vermis (BV) angle and brainstem-tentorium (BT) angle and to assess the correlation among these angles, fetal gender and gestational age (GA) in 221 fetuses between 20 and 37 wk. The angles of the BV and BT were measured on the mid-sagittal view of the fetal head in normally developed Chinese fetuses. The ultrasound measurements, the fetal gender and the GA were collected for statistical analysis. Rank sum test revealed no significant differences in the measurements of the BV and the BT angles with respect to gender (all p > 0.05). Spearman rank correlation analysis showed no GA effect on the BV and the BT angles with correlation coefficients (r) of 0.05 (p > 0.05) and 0.09 (p > 0.05). The 95% reference ranges of the BV and the BT angles were 8.7° (4.5°-18.0°) and 28.0° (21.3°-43.8°), respectively. The newly established reference ranges may facilitate differential diagnosis of fetuses with suspected posterior fossa anomalies in the second and third trimesters.

Nomograms of cerebellar vermis height and transverse cerebellar diameter in appropriate-for-gestational-age neonates

BACKGROUND

Evaluation of cerebellar morphology and measurement of its biometric parameters such as cerebellar vermis height and transverse cerebellar diameter may assist the neonatologist in monitoring cerebellar growth and development and detect abnormalities resulting from malformations, hemorrhage or ischemic infarction.

AIM

The aim of this study was to establish nomograms of cerebellar vermis height and transverse cerebellar diameter at birth in appropriate-for-gestational-age neonates by using cranial ultrasonography.

STUDY DESIGN

A cross-sectional observational study. Appropriate-for-gestational-age neonates were evaluated with cranial ultrasonography by the same neonatal sonographer.

SUBJECTS

Healthy appropriate-for-gestational-age neonates born between 26 and 42 weeks of gestation in their first postnatal 24 h.

OUTCOME MEASURES

Cranial sonographic measurements included cerebellar vermis height measured midsagitally from anterior fontanelle and transverse cerebellar diameter measured coronally from mastoid fontanelle. Measurements were taken for each gestational age between 26 and 42 weeks and nomograms were constructed.

RESULTS

Three hundred twenty-one consecutively born appropriate-for-gestational-age neonates (163 females and 158 males) were studied. A linear growth function was observed between vermis height and gestational age and between transverse cerebellar diameter and gestational age.

CONCLUSION

Nomograms of cerebellar vermis height and transverse cerebellar diameter against gestational age at birth in appropriate-for-gestational-age neonates have been constructed. This can help the neonatologist to assess variations from the normal during ongoing cerebellar growth and development and to diagnose cerebellar anomalies.

Early pregnancy scanning for fetal anomalies--the new standard?

For many years, significant efforts have been made toward attempts at early detection of chromosomal and structural malformations, to lower the rate of these defects in newborns. Traditionally, the main ultrasound examination during pregnancy was performed in the second trimester, using transabdominal transducers. The development of high-frequency and high-resolution (5 to 9 MHz; 6 to 12 MHz) transvaginal probes along with substantial improvements in image and signal processing have opened new possibilities for the investigation of early pregnancy. Up until the recent past, many defects were considered unidentifiable early in pregnancy. A large number of those can now be diagnosed already in the first trimester. Early detection of fetal anomalies enables karyotyping by chorionic villus sampling and, in those patients in whom findings are abnormal, simpler procedures for termination of pregnancy may be performed. This may reduce physical and psychological morbidity associated with second-trimester abortions.

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.

Assessment of cerebellar vermis biometry at 18-32 weeks of gestation by three-dimensional ultrasound examination

OBJECTIVE

The purpose of this study was to construct reference limits for cerebellar vermis (CV) dimensions measured on images reconstructed from three-dimensional (3D) ultrasonography and to evaluate these measurements reproducibility.

METHODS

3D ultrasound volumes were acquired transabdominally from an axial view of the fetal head in 342 fetuses cross-sectionally studied between 18 to 32 weeks of gestation. Offline analysis of fetal brain midsagittal plane was used to evaluate length and area of CV. The agreement between two-dimensional (2D) and 3D measurements as well as the interobserver variability in 3D measurements were assessed by interclass correlation coefficients (ICC).

RESULTS

Adequate visualization of the midsagittal plane was obtained in 96.7% of the fetuses. CV length (r = 0.89, p < 0.0001) and CV area (r = 0.93, p < 0.0001) showed a significant linear growth with gestation. A good agreement was found between measurements from either 2D or 3D ultrasound views (CV length ICC 0.943, CV area ICC 0.940) as well as between measured obtained by different observers (CV length ICC 0.965, CV area ICC 0.905).

CONCLUSIONS

Measurements of the CV can be obtained from the midsagittal plane of fetal brain reconstructed from 3D volumes acquired transabdominally. The constructed nomograms may facilitate the diagnosis of cerebellar abnormalities.

The fetal cerebellum: development and common malformations

The cerebellum undergoes a protracted development, making it particularly vulnerable to a broad spectrum of developmental events. Acquired destructive and hemorrhagic insults may also occur. The main steps of cerebellar development are reviewed. The normal imaging patterns of the cerebellum in prenatal ultrasound and magnetic resonance imaging (MRI) are described with emphasis on the limitations of these modalities. Because of confusion in the literature regarding the terminology used for cerebellar malformations, some terms (agenesis, hypoplasia, dysplasia, and atrophy) are clarified. Three main pathologic settings are considered and the main diagnoses that can be suggested are described: retrocerebellar fluid enlargement with normal or abnormal biometry (Dandy-Walker malformation, Blake pouch cyst, vermian agenesis), partially or globally decreased cerebellar biometry (cerebellar hypoplasia, agenesis, rhombencephalosynapsis, ischemic and/or hemorrhagic damage), partially or globally abnormal cerebellar echogenicity (ischemic and/or hemorrhagic damage, cerebellar dysplasia, capillary telangiectasia). The appropriate timing for performing MRI is also discussed.

Development of the human fetal cerebellum in the second trimester: a post mortem magnetic resonance imaging evaluation

The cerebellum is one of the most important structures in the posterior cranial fossa, but the characterization of its development by magnetic resonance imaging (MRI) is incomplete. We scanned 40 fetuses that had no morphological brain disorder at 14-22 weeks of gestation using 7.0 T MRI. Amira 4.1 software was used to determine morphological parameters of the fetal cerebellum, which included the cerebellar volume (CV), transverse cerebellar diameter (TCD), and the length and width of the vermis. The relationship between these measurements and gestational age (GA) was analysed. We found that the primary fissure was visible at week 14 of gestation. From week 16, the prepyramidal fissure, the secondary fissure and the dentate nucleus could be identified. The posterolateral fissure and the fourth ventricle were recognized at week 17, whereas the tentorium of the cerebellum was visible at week 20. The relationships between GA and CV, TCD, and the width and length of the vermis were described adequately by second-order polynomial regression curves. The ratios between TCD and vermis length and between TCD and vermis width decreased with GA. These results show that 7.0 T MRI can show the trajectory of cerebellar development clearly. They increase our understanding of normal cerebellar development in the fetus, and will facilitate the diagnosis of pathological intrauterine changes in the cerebellum.

Sonographic examination of the fetal vermis: tricks for obtaining the narrow midline target with 3-dimensional volume contrast imaging in the C plane

Prenatal imaging of the fetal cerebellar vermis is challenging even for experienced examiners. We found that by aiming the ultrasound beam through the mastoid fontanel and then rotating the data set in a multiplanar reconstruction and applying volume contrast imaging in the C plane, we were consistently able to obtain images of the vermis in the standard midsagittal plane. Images of the fetal vermis suitable for morphologic evaluation were obtained in 408 of 414 cases (98.5%) at gestational ages of 18 weeks to 31 weeks 6 days; the examination time was only minimally increased.

Cerebral measurements made using cranial ultrasound in term Ugandan newborns

BACKGROUND

Few cUS studies of cerebral measurements are available for normal term infants. Normative data is important for evaluating cerebral structure size in symptomatic term infants and assessing preterm brain growth by term age.

OBJECTIVES

To (i) make linear measurements using cranial ultrasound (cUS) for major cerebral structures and intracranial spaces in normal newborn term infants, (ii) correlate these measurements with gestational age (GA), birth weight (BW), head circumference (HC), gender and within one infant (iii) examine inter/intra-observer variation, and (iv) compare these data with those currently available.

DESIGN, SETTING AND PATIENTS

Linear cUS measurements of major cerebral structures were made in well term-born Ugandan infants at Mulago University Hospital, Kampala. Correlations between the measurements and gender, HC, BW and GA were calculated. Intra- and inter-observer agreements were assessed.

RESULTS

Data from 106 infants (mean GA 39.20±1.4SD weeks) were analysed. Intra/inter-observer agreement was substantial/excellent. Significant correlations were found between HC and pons anterior-posterior diameter (p<0.01), corpus callosal (CC) length (p=0.02) and transverse cerebellar diameter (TCD, p<0.01) and between BW and CC length (p=0.02), vermis height (<0.01) and thalamo-occipital distance (p=0.03); no significant correlation was found with GA. Within infants CC length and TCD correlated significantly (p=0.019). Males had larger left ventricular indices than females (p=0.04). The data was similar to those from other populations.

CONCLUSIONS

These data provide reliable reference values for linear measurements of many cerebral structures made using cUS. The data agree well with those from other populations suggesting that cerebral size is similar in different ethnic groups.

Posterior fossa malformations: main features and limits in prenatal diagnosis

Posterior fossa (PF) malformations are commonly observed during prenatal screening. Their understanding requires knowledge of the main steps of PF development and knowledge of normal patterns in US and MR imaging. The vast majority of PF malformations can be strongly suspected by acquiring a midline sagittal slice and a transverse slice and by systematically scrutinizing the elements of the PF: cerebellar vermis, hemispheres, brainstem, fourth ventricle, PF fluid spaces and tentorium. Analysis of cerebellar echogenicity and biometry is also useful. This review explains how to approach the diagnosis of the main PF malformations by performing these two slices and answering six key questions about the elements of the PF. The main imaging characteristics of PF malformations are also reviewed.

Sonographic measurements of the fetal fastigium between 20 and 40 weeks' gestation

OBJECTIVE

The purpose of this study was to establish a new reference angle chart for fastigial biometric measurements throughout gestation in normal singleton pregnancies.

METHODS

A prospective cohort study was designed. A total of 505 pregnant women between 20 and 40 weeks' gestation were included in the study. Excluded were those with multiple pregnancies, congenital anomalies, abnormal karyotypes, and polyhydramnios or oligohydramnios. Transvaginal or transabdominal sonography was performed in the midsagittal plane of the brain.

RESULTS

The angle of the fastigium was found to be 30 degrees to 60 degrees throughout pregnancy. These data were found to be constant during the progression of pregnancy without any significant changes.

CONCLUSIONS

Fastigial measurements throughout pregnancy are presented. Its angle is constant throughout pregnancy. Evaluation of the fastigium may assist in cases of subtle posterior fossa anomalies.

Fetal cerebellar volume and symmetry on 3-d ultrasound: volume measurement with multiplanar and vocal techniques

The purpose of this prospective longitudinal study was to evaluate the growth of the fetal cerebellar volume by means of 3-D ultrasound to evaluate whether there is a difference between the volumes of the left and right cerebellar hemispheres, and to evaluate the intra- and interobserver reliability of two different techniques of volume measurement. Three-dimensional ultrasound examinations were performed every two to three weeks on 27 fetuses between 20 and 40 weeks' gestation. Measurements of the total cerebellar volume and of the left and right cerebellar hemispheres were done using the multiplanar technique. Multilevel analysis was used to determine the growth of cerebellar volume based on individual developmental trajectories and compare the volume of the right and left hemispheres of the cerebellum. The intra- and interobserver reliability was calculated for the multiplanar and VOCAL techniques in a subgroup of 10 fetuses. A nonlinear growth curve of cerebellar volume in normal pregnancy was generated. The cerebellar growth per two-week decreased from a gain of 51% of the first measurement at 20 weeks to a gain of 16% of the first measurement at 38 weeks. The left cerebellar hemisphere was significantly larger (12.3%, p < 0.01) than the right. The intraclass correlation coefficient for the measurements by the two techniques was 0.99. Intraobserver reliability: the intraclass correlation coefficient for the measurements using the multiplanar technique was 0.96 and 0.97 and for VOCAL it was 0.98 and 0.97 for the two observers, respectively. Interobserver reliability: the intraclass correlation coefficient for the measurements using the multiplanar technique was 0.97 and for VOCAL 0.98. Longitudinal growth curves based on individual developmental trajectories were generated for the cerebellar volume. The left fetal cerebellar hemisphere was found to be significantly larger than the right. Both multiplanar and VOCAL techniques had a good intra- and interobserver reliability and yielded very similar results.

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.

Nomogram of the cerebellar vermis height at birth in small-for-gestational-age neonates

AIM

To establish a nomogram of the height of the cerebellar vermis at birth in small-for-gestational-age neonates.

METHODS

Eighty-five consecutively born healthy singletons who were small for gestational age were enrolled in a cross-sectional observational study. The height of the cerebellar vermis was measured by ultrasonography in the midsagittal plane. Reference intervals for the vermian height at 5th, 50th and 95th centiles were estimated at any week of gestational age using a mean and standard deviation model based on least squares polynomial regression.

RESULTS

All attempts at obtaining neonatal vermian height were successful. Mean (standard deviation) maternal age was 29.6 (4.7) years; median parity was 1 (range, 1-3). No difference was found between males and females for the vermian height (mean difference [95% confidence interval], -0.03 [-0.16; 0.10] cm). Mean vermian height (in cm) against gestational age (in weeks) was suitably modelled by a quadratic-cubic polynomial (r2= 0.790, p < 0.0001) as 0.712 + 0.00129 x gestational age2- 0.0000053 x gestational age3 (SD =-1.009 + 0.0504 x gestational age -0.000014 x gestational age3).

CONCLUSION

A nomogram of the height of the cerebellar vermis at birth against gestational age was established for use in small-for-gestational-age neonates.

Height of the cerebellar vermis and gestational age at birth

OBJECTIVES

The objective of this study was to construct reference ranges of the neonatal cerebellar vermis height with respect to the gestational age at birth.

METHODS

This observational study assessed 434 neonates born at 25-42 weeks' gestation. The neonates were singleton and appropriate in size for gestational age, and did not exhibit any abnormalities or neonatal disease. Gestational age was based on the date of the last menstrual period and confirmed by ultrasound examination performed within the 12(th) week of pregnancy. Sonographic measurements of the height of the cerebellar vermis in the mid-sagittal plane were performed within 24 h of birth by the same neonatal sonographer. Reference ranges (5(th), 50(th) and 95(th) centiles) were estimated by a mean and SD model based on least-squares polynomial regression.

RESULTS

Neonatal sonographic measurements were obtained in all cases. Mean (SD) maternal age was 30.2 (4.3) years. Mean cerebellar vermis height adjusted for gestational age did not differ between males and females, the mean adjusted difference being 0.012 (95% CI, - 0.009 to 0.033) cm. Mean cerebellar vermis height (cm) against gestational age (weeks) was suitably modeled by a linear-cubic polynomial as - 1.784 + 0.137 x GA - 0.000019 x GA(3) (SD = - 0.147 + 0.008 x GA), where GA = gestational age.

CONCLUSIONS

Reference ranges for the height of the cerebellar vermis at birth with respect to gestational age at birth have been constructed in appropriate-for-gestational-age neonates.

Dandy-Walker malformation complex: correlation between ultrasonographic diagnosis and postmortem neuropathology

OBJECTIVE

This autopsy-based study was designed to evaluate sonographic and neuropathologic findings of fetuses diagnosed prenatally with Dandy-Walker malformation complex.

METHODS

The retrospective study encompassed a series of 44 autopsy cases from 2 tertiary referral centers with a prenatal ultrasound diagnosis of Dandy-Walker malformation complex between 1995 and 2003. Ultrasound and pathology data from the cases and from age-matched controls were reviewed in a blinded manner. An unequivocal diagnosis of Dandy-Walker malformation complex from ultrasonography or pathology archival images required significant hypoplasia or aplasia of the cerebellar vermis.

RESULTS

Neuropathologic examination failed to confirm the prenatal diagnosis of Dandy-Walker malformation complex in 59% (26/44, 95% confidence interval [CI] 44-72) of the cases. After standardized reevaluation of high quality archival sonograms and pathology images, concordance remained poor at 55% (6/11 cases, 95% CI 28-79). Sonographic features that favored concordance included marked enlargement of the cisterna magna (> or = 10 mm), complete aplasia of the vermis, and a trapezoid-shaped gap between the cerebellar hemispheres. This latter finding contrasted with a keyhole-shaped gap in fetuses with no cerebellar neuropathology.

CONCLUSION

Correlation between a prenatal ultrasound diagnosis of Dandy-Walker malformation complex and autopsy neuropathology findings is poor. Unequivocal prenatal sonographic diagnosis of Dandy-Walker malformation complex should be reserved for cases with the classic findings of Dandy-Walker malformation, including enlargement of the cisterna magna, aplasia of the vermis, and a trapezoid-shaped, rather than keyhole-shaped, interhemispheric gap.

LEVEL OF EVIDENCE

III.

The Fetal Cerebellar Vermis

Fetal magnetic resonance provides a new tool in the imaging of the posterior fossa and is proving useful in cases that are difficult to assess sonographically by allowing further assessment of the fourth ventricle, cisterna magna, and vermian growth and development. We describe various criteria with which to evaluate vermian growth, including vermian biometry and the relationship between the superior and inferior lobes. We demonstrate 2 markers of normal vermian development: the primary fissure and fastigial point. We illustrate the tegmento-vermian angle, "closure" of the fourth ventricle, and communication of the fourth ventricle with the basal cisterns during development and in several disorders. We correlate those features with the expected embryological course of development and illustrate identification of these features and associated abnormalities of the posterior fossa, brain stem, and central nervous system in mid-trimester scans of fetuses with abnormal development. Correlation with contemporaneous ultrasound examinations is demonstrated.

Structural linear measurements in the newborn brain: accuracy of cranial ultrasound compared to MRI

BACKGROUND

Structural size in the neonatal brain is of clinical importance. Cranial ultrasonography (cUS) is the primary method used for evaluating the neonatal brain and it is important to know whether linear measurements made using this technique are accurate.

OBJECTIVE

To compare linear measurements of different cerebral structures made from neonatal cUS and contemporaneous MRI.

MATERIALS AND METHODS

Preterm and term infants studies with cUS and MRI on the same day were studied. Linear measurements made using both techniques from many cerebral structures were compared using a paired t-test.

RESULTS

A total of 44 sets of scans from 26 preterm and 8 term infants were assessed. Small but significant differences between the cUS and MRI measurements (P<0.05) were found for the ventricular index, the posterior horn depth of the lateral ventricle, the extracerebral space and interhemispheric fissure, and the cortex of the cingulate gyrus. No significant differences were found for any other measurements.

CONCLUSION

Linear measurements from cUS are accurate for most neonatal cerebral structures. Significant differences compared to MRI were found for a few structures, but only for the cortex were the absolute differences marked and possibly of clinical importance.

Comparison between magnetic resonance imaging and fetopathology in the evaluation of fetal posterior fossa non-cystic abnormalities

OBJECTIVES

To compare magnetic resonance imaging (MRI) and fetopathological findings in the evaluation of non-cystic fetal posterior fossa anomalies and to describe associated abnormalities.

METHODS

This was a prospective study from 2000 to 2005 of fetuses identified on ultrasound as having sonographic suspicion of posterior fossa malformation. All underwent a thorough MRI examination of the fetal brain, after which we classified each fetus as presenting one of the following pathologies: vermian hypoplasia or agenesis, cerebellar and/or brain stem hypoplasia, destructive or dysplastic lesions. All of the pregnancies were then terminated, after which the whole fetus underwent fetopathological examination. We compared the findings from MRI and fetopathological examinations and recorded the associated cerebral and extracerebral abnormalities.

RESULTS

Twenty-five fetuses were included. MRI was performed at a mean gestational age of 31 weeks, and fetopathological examination at 33 weeks. In 12 cases we observed vermian hypoplasia, six had partial vermian agenesis, 11 had cerebellar hemisphere hypoplasia, seven had brain stem hypoplasia, four had destructive lesions and six had dysplastic lesions. The two techniques were similar in their performance with respect to the detection of vermian agenesis, brain stem hypoplasia and destructive lesions. There were four false-positive results of MRI for vermian hypoplasia and a poor agreement regarding cerebellar hemisphere hypoplasia. No dysplastic lesions were diagnosed by MRI. None of the posterior fossa malformations was isolated and many cerebral and extracerebral abnormalities were found.

CONCLUSION

A systematic analysis of the posterior fossa in fetal MRI makes it possible to diagnose accurately most posterior fossa malformations. These malformations never occurred in isolation in our study.

Isolated posterior cerebellar vermal defect: a morphological study of midsagittal cerebellar vermis in 4 fetuses--early stage of Dandy-Walker continuum or new vermal dysgenesis?

This report is a neuropathological description of posterior cerebellar vermis agenesis/hypoplasia at midgestation. This defect was demonstrated by prenatal ultrasound in four 21- to 24-week-old fetuses. Neuropathological findings were characterized macroscopically by hypoplasia of the posterior vermis with normal cerebellar hemispheres and brainstem; hypoplasia of the posterior vermian lobules 6 to 10, mildly cystic dilatation of the ventricular cavity, and a flat profile of the roof of the fourth ventricle also were demonstrated. Microscopically, a hypercellular and abnormally located germinal matrix and abnormal migration of external granule cell precursors into the meningeal tissue above the outer surface of the cerebellum were found. These abnormalities might result in delayed growth and foliation of the posterior vermian lobules. This feature might be the neuropathological pattern of the early stage of the Dandy-Walker continuum, although it cannot be excluded as a consequence of a primary developmental failure of the vermal primordium.

Fetal Magnetic Resonance Imaging as a Complement to Fetal Ultrasonography

Ultrasonography is the screening method of choice for the evaluation of the fetus. It is safe, inexpensive, and easily performed. However, it is operator dependent, and evaluation may be limited because of fetal position, maternal obesity, overlying bone, and/or oligohydramnios. Magnetic resonance imaging is an alternative modality that uses no ionizing radiation, has excellent tissue contrast and a large field of view, is not limited by obesity or overlying bone, and can image the fetus in multiple planes, no matter the fetal lie. Faster scanning techniques allow studies to be performed without sedation in the second and third trimester with minimal motion artifact.

Nomograms of the axial fetal cerebellar hemisphere circumference and area throughout gestation

OBJECTIVE

The widely applied transcerebellar diameter (TCD) obtained at axial cranial imaging, measures the distance between the lateral aspects of the cerebellum and incorporates the width of the cerebellar vermis. Our objective was to create reference ranges of axial fetal cerebellar hemisphere circumference (CHC) and area (CHA), independent of the cerebellar vermis, throughout gestation.

METHODS

This cross-sectional study involved pregnant patients between 14 and 41 weeks of gestation. Inclusion criteria consisted of well-established dates (confirmed by early ultrasound), non-anomalous singleton fetuses and intact amniotic membranes. Sonographic measurements included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), humerus length (HL), TCD, and estimated fetal weight (EFW). Values of axial fetal CHC and CHA were each calculated as the mean of three separate measurements. The 5th, 50th and 95th centiles were estimated at each week of gestational age (GA) by least-squares regression for the mean and standard deviation (SD) of the CHC and CHA as functions of GA. r2 and associated P-values for the relationships of CHC and CHA with other sonographic biometric measurements were calculated.

RESULTS

The study included 651 consecutive patients. All attempts at obtaining axial fetal CHC and CHA were successful. Mean maternal age was 27.3+/-6.7 years, median gravidity was 1 (range 1-16), and median parity was 1 (range 0-6). Mean CHC (cm) throughout gestation was modeled as -2.091+0.2563xGA (weeks) (SD=-0.075+0.0164xGA), and mean CHA (cm2) was modeled as 0.245-0.0765xGA+0.00506xGA2 (SD=1.167-0.1565xGA+0.006785xGA(2)-0.00008028xGA3). Fetal axial CHC and CHA correlated significantly and strongly with BPD, HC, AC, HL, FL, TCD and EFW (all R2 values were >or=0.95, and all P-values were <0.001).

CONCLUSION

Nomograms of axial fetal cerebellar hemisphere circumference and area throughout gestation, independent of the cerebellar vermis, have been provided.

Magnetic resonance imaging of fetal cerebellar development

In the last few years fetal magnetic resonance imaging (MRI) has been proposed as a second level technique in the evaluation of fetal brain anomalies. It has been demonstrated that MRI is highly accurate in illustrating the morphologic changes of developing brain and fetal brain abnormalities being a useful procedure when ultrasonography is inconclusive or doubtful. Starting from the 19-20 weeks gestational age (GA), MRI can reliably depict fetal brain anatomy and locating pathology, offering a robust and reliable tool in the assessment of fetal CNS diseases. In this review both in vivo MRI quantitative and qualitative data about fetal cerebellar development are presented and compared with ultrasonography data. Fetal cerebellar development is gradual, steady, and largely comparable to the development of the supratentorial brain. Archicerebellar (flocculo-nodular lobe) and paleocerebellar (vermis) structures develop first, whereas neocerebellum (cerebellar hemispheres) develop slowly and largely after birth.

Posterior fossa and vermian morphometry in the characterization of fetal cerebellar abnormalities: a prospective three-dimensional ultrasound study

OBJECTIVES

To assess whether, by applying a predefined set of morphometric measurements to the posterior fossa and the cerebellar vermis, it is possible to detect and quantify the following parameters, which represent key features of abnormalities of the vermis and posterior fossa: 1) upward rotation of the vermis; 2) upward displacement of the tentorium; 3) underdevelopment of the vermis. Also to assess, in a small subset of cases, the correlation between ultrasound and magnetic resonance imaging (MRI) in the measurement of these three parameters.

METHODS

This was a prospective observational trial. The study population included 51 normal fetuses and 20 abnormal fetuses with Dandy-Walker malformation (n = 5), Dandy-Walker variant (n = 8) or megacisterna magna (n = 7). Three-dimensional (3D) ultrasound volumes of the fetal head were acquired from the posterior fontanelle or the posterior part of the sagittal suture and processed offline with dedicated software. The following parameters were analyzed: tentorovermian angle; tentoroclivus angle; clivovermian angle; vermian diameter/biparietal diameter x 100 ratio (VD/BPD ratio). In seven cases, MRI performed on the same day as sonography was available for comparison. Non-parametric statistics were used to assess differences in means and correlations.

RESULTS

The tentoroclivus angle was increased only in fetuses with Dandy-Walker malformation (P < 0.001). Upward rotation of the vermis was demonstrated both by the tentorovermian and the clivovermian angles in fetuses with Dandy-Walker variant (P < 0.001), while in those with Dandy-Walker malformation the difference was not statistically significant, probably due to the small number of cases. Finally, the VD/BPD ratio demonstrated that the degree of vermian hypoplasia was higher in Dandy-Walker malformation compared with Dandy-Walker variant (P < 0.001).

CONCLUSIONS

Using 3D ultrasound, we have demonstrated in the fetus the key elements characterizing most anomalies of the posterior fossa, namely the upward displacement of the tentorium, the counterclockwise rotation and the significant hypoplasia of the cerebellar vermis. In addition, our observations in a small number of cases indicate that there is a good correlation between MRI- and 3D ultrasound-derived morphometric measurements of the vermis.

Rotation of the vermis as a cause of enlarged cisterna magna on prenatal imaging

OBJECTIVES

Dandy-Walker complex is a continuum of developmental anomalies of the posterior fossa which includes vermian rotation. However, vermian rotation alone may be benign. The aim of this study was to describe our experience with sagittal-plane prenatal ultrasound in the diagnosis of rotation of the vermis in cases of suspected enlarged cisterna magna on routine antenatal imaging, and to describe the follow-up of these patients.

METHODS

Seven women, who were referred to our ultrasound unit for evaluation of an enlarged fetal cisterna magna and suspected agenesis of the vermis on axial-plane imaging, underwent further multiplanar studies of the posterior fossa and measurements of the vermis.

RESULTS

The mean maternal age was 27 (range, 20-33) years and the mean gestational age at diagnosis was 19.5 (range, 18-31) weeks. The standard axial plane image showed a 'direct communication' between the cisterna magna and the fourth ventricle. In the mid-sagittal plane, the vermis was clearly delineated, with posterosuperior rotation. Vermis size was within normal limits for gestational age in all cases. Findings were confirmed by prenatal magnetic resonance imaging (MRI) in two cases and postnatal MRI and/or sonography in five. During a mean follow-up of 4.5 (range, 1-7.5) years, all children developed normally, with no neurological complications.

CONCLUSION

The finding of an enlarged cisterna magna on standard- (axial-)plane ultrasound should be evaluated further in the sagittal plane to determine whether the cause is rotation of a normal vermis. This may spare patients unnecessary tests, anxiety and, in some cases, pregnancy termination.

Fetal Posterior Fossa Volume: Assessment with MR Imaging

PURPOSE

To retrospectively determine the relationship between posterior fossa volume (PFV) and estimated gestational age (EGA) and/or femur length (FL) during pregnancy for the purpose of developing a normal growth curve.

MATERIALS AND METHODS

Advance institutional review board approval was obtained for this HIPAA-compliant study, and the need for parent informed consent was waived. A cross-sectional retrospective study was performed to measure PFV on in vivo magnetic resonance (MR) images obtained in 76 fetuses of 18-36 weeks gestation who had a morphologically normal CNS. Because this was a retrospective series, MR imaging techniques varied slightly, but all fetuses underwent imaging at contiguous 3-5-mm intervals in at least two orthogonal planes, with repetition time msec/echo time msec, 5-12/62-95; number of signals acquired, one; flip angle, 150 degrees -180 degrees; and matrix, 128-192 x 256. Posterior fossa areas were manually traced on half-Fourier rapid acquisition with relaxation enhancement in utero fetal MR images by one observer. PFVs were then calculated by manually summing areas from the contiguous sections and multiplying the total area by the section thickness. An average PFV (APFV) across orthogonal planes was calculated for each fetus, and the relationship between APFV and EGA was mathematically modeled. Coronal, transverse, and sagittal views were compared with correlations and Bland-Altman plots. Two additional observers repeated the measurements for a small subset of fetuses (n = 5). Paired t test analyses were also performed to determine significant differences between sagittal, transverse, and coronal measurements, as well as to determine preliminary intraobserver and interobserver variability of measurements in a subset of cases.

RESULTS

The relationship between APFV (in cubic centimeters) and EGA (in weeks) was well described by a single exponential function [APFV = 0.689 exp(EGA/9.10)]. APFV doubling time was 6.31 weeks. Root-mean-square variation of values around the model line was 1.63 cm(3). There was no statistically significant intra- or interobserver variation (P > .16 for all fetuses) at preliminary analysis. No correlation between APFV and FL could be found.

CONCLUSION

The normal fetal PFV growth curve generated in this study may have potential as a model for clinical application.

The fetal cerebellar vermis: anatomy and biometric assessment using volume contrast imaging in the C-plane (VCI-C)

OBJECTIVES

To describe the normal appearance and study the biometry of the fetal cerebellar vermis by three-dimensional (3D) volume contrast imaging in the coronal (C-) plane (VCI-C).

METHODS

A total of 203 normally developed fetuses were examined prospectively at 18-33 weeks' gestation. At the level of the view used to measure the transverse cerebellar diameter (TCD), a VCI-C plane was displayed to examine, using a transabdominal probe, the fetal mid-saggital vermis. The volumes acquired were stored for later review and measurement of the anteroposterior (AP) diameter, craniocaudal (CC) diameter and surface area of the cerebellar vermis. Each dataset was evaluated by two independent observers. Measurements as a function of gestational age (GA), biparietal diameter (BPD), head circumference (HC) and TCD were expressed by regression equations. Interobserver variability was evaluated. Nomograms were produced. In order to validate the use of VCI in fetal biometry, datasets from 57 patients were selected arbitrarily for comparison of their VCI-C measurements with those from mid-sagittal sections of a stored 3D multiplanar examination. Intraclass correlation was used to evaluate the agreement between these measurements.

RESULTS

The mean maternal age was 32 years. We were able to measure mid-sagittal CC diameter, mid-sagittal AP diameter and cerebellar vermis surface area in all fetuses. Interobserver variability analysis showed no significant differences between the two observers (P > 0.05). Measurements of the cerebellar vermis (AP diameter, CC diameter and surface area) correlated linearly with GA, BPD, HC and TCD (r > or = 0.82, P < 0.0001). CC and AP diameters estimated from the mid-sagittal section of the multiplanar measurements were significantly correlated with VCI-C measurements (r = 0.96, P < 0.00001 and r = 0.95, P < 0.00001, respectively).

CONCLUSIONS

VCI-C is a valuable tool, allowing intrauterine assessment of the normal appearance of the fetal cerebellar vermis. The nomograms developed in this study should enable accurate evaluation of the cerebellar vermis.

Prenatal diagnosis in pregnancies at risk for Joubert syndrome by ultrasound and MRI

OBJECTIVES

To describe the prenatal imaging findings in fetuses at risk for Joubert syndrome (JS), review the literature and propose a protocol for prenatal diagnosis of JS using ultrasound and MRI.

METHODS

We reviewed prenatal ultrasound and fetal MRI studies in two pregnancies at 25% recurrence risk for JS and correlated these findings with gross neuropathology in one affected fetus.

RESULTS

While abnormalities such as occipital encephalocele or enlarged cisterna magna have been identified before mid-trimester, the definitive diagnosis of JS, based on core cerebellar findings, has only been possible after 17 weeks' gestation.

CONCLUSIONS

With longitudinal monitoring, it is possible to diagnose JS in at-risk pregnancies before 24 weeks' gestation. On the basis of our data and review of the literature, we propose a protocol for monitoring pregnancies at risk for JS, utilizing serial ultrasounds combined with fetal MRI at 20-22 weeks' gestation to maximize the accuracy of prenatal diagnosis.