MRI of the Fetal Brain

High-resolution anatomical imaging of the fetal brain with a reduced field of view using outer volume suppression

PURPOSE

To achieve high-resolution fetal brain anatomical imaging without introducing image artifacts by reducing the FOV, and to demonstrate improved image quality compared to conventional full-FOV fetal brain imaging.

METHODS

Reduced FOV was achieved by applying outer volume suppression (OVS) pulses immediately prior to standard single-shot fast spin echo (SSFSE) imaging. In the OVS preparation, a saturation RF pulse followed by a gradient spoiler was repeated three times with optimized flip-angle weightings and a variable spoiler scheme to enhance signal suppression. Simulations and phantom and in-vivo experiments were performed to evaluate OVS performance. In-vivo high-resolution SSFSE images acquired using the proposed approach were compared with conventional and high-resolution SSFSE images with a full FOV, using image quality scores assessed by neuroradiologists and calculated image metrics.

RESULTS

Excellent signal suppression in the saturation bands was confirmed in phantom and in-vivo experiments. High-resolution SSFSE images with a reduced FOV acquired using OVS demonstrated the improved depiction of brain structures without significant motion and blurring artifacts. The proposed method showed the highest image quality scores in the criteria of sharpness, contrast, and artifact and was selected as the best method based on overall image quality. The calculated image sharpness and tissue contrast ratio were also the highest with the proposed method.

CONCLUSION

High-resolution fetal brain anatomical images acquired using a reduced FOV with OVS demonstrated improved image quality both qualitatively and quantitatively, suggesting the potential for enhanced diagnostic accuracy in detecting fetal brain abnormalities in utero.

Review on deep learning fetal brain segmentation from Magnetic Resonance images

Brain segmentation is often the first and most critical step in quantitative analysis of the brain for many clinical applications, including fetal imaging. Different aspects challenge the segmentation of the fetal brain in magnetic resonance imaging (MRI), such as the non-standard position of the fetus owing to his/her movements during the examination, rapid brain development, and the limited availability of imaging data. In recent years, several segmentation methods have been proposed for automatically partitioning the fetal brain from MR images. These algorithms aim to define regions of interest with different shapes and intensities, encompassing the entire brain, or isolating specific structures. Deep learning techniques, particularly convolutional neural networks (CNNs), have become a state-of-the-art approach in the field because they can provide reliable segmentation results over heterogeneous datasets. Here, we review the deep learning algorithms developed in the field of fetal brain segmentation and categorize them according to their target structures. Finally, we discuss the perceived research gaps in the literature of the fetal domain, suggesting possible future research directions that could impact the management of fetal MR images.

Geometric Reliability of Super-Resolution Reconstructed Images from Clinical Fetal MRI in the Second Trimester

Fetal Magnetic Resonance Imaging (MRI) is an important noninvasive diagnostic tool to characterize the central nervous system (CNS) development, significantly contributing to pregnancy management. In clinical practice, fetal MRI of the brain includes the acquisition of fast anatomical sequences over different planes on which several biometric measurements are manually extracted. Recently, modern toolkits use the acquired two-dimensional (2D) images to reconstruct a Super-Resolution (SR) isotropic volume of the brain, enabling three-dimensional (3D) analysis of the fetal CNS.We analyzed 17 fetal MR exams performed in the second trimester, including orthogonal T2-weighted (T2w) Turbo Spin Echo (TSE) and balanced Fast Field Echo (b-FFE) sequences. For each subject and type of sequence, three distinct high-resolution volumes were reconstructed via NiftyMIC, MIALSRTK, and SVRTK toolkits. Fifteen biometric measurements were assessed both on the acquired 2D images and SR reconstructed volumes, and compared using Passing-Bablok regression, Bland-Altman plot analysis, and statistical tests.Results indicate that NiftyMIC and MIALSRTK provide reliable SR reconstructed volumes, suitable for biometric assessments. NiftyMIC also improves the operator intraclass correlation coefficient on the quantitative biometric measures with respect to the acquired 2D images. In addition, TSE sequences lead to more robust fetal brain reconstructions against intensity artifacts compared to b-FFE sequences, despite the latter exhibiting more defined anatomical details.Our findings strengthen the adoption of automatic toolkits for fetal brain reconstructions to perform biometry evaluations of fetal brain development over common clinical MR at an early pregnancy stage.

Review of deep learning and artificial intelligence models in fetal brain magnetic resonance imaging

Central nervous system abnormalities in fetuses are fairly common, happening in 0.1% to 0.2% of live births and in 3% to 6% of stillbirths. So initial detection and categorization of fetal Brain abnormalities are critical. Manually detecting and segmenting fetal brain magnetic resonance imaging (MRI) could be time-consuming, and susceptible to interpreter experience. Artificial intelligence (AI) algorithms and machine learning approaches have a high potential for assisting in the early detection of these problems, improving the diagnosis process and follow-up procedures. The use of AI and machine learning techniques in fetal brain MRI was the subject of this narrative review paper. Using AI, anatomic fetal brain MRI processing has investigated models to predict specific landmarks and segmentation automatically. All gestation age weeks (17-38 wk) and different AI models (mainly Convolutional Neural Network and U-Net) have been used. Some models' accuracy achieved 95% and more. AI could help preprocess and post-process fetal images and reconstruct images. Also, AI can be used for gestational age prediction (with one-week accuracy), fetal brain extraction, fetal brain segmentation, and placenta detection. Some fetal brain linear measurements, such as Cerebral and Bone Biparietal Diameter, have been suggested. Classification of brain pathology was studied using diagonal quadratic discriminates analysis, K-nearest neighbor, random forest, naive Bayes, and radial basis function neural network classifiers. Deep learning methods will become more powerful as more large-scale, labeled datasets become available. Having shared fetal brain MRI datasets is crucial because there aren not many fetal brain pictures available. Also, physicians should be aware of AI's function in fetal brain MRI, particularly neuroradiologists, general radiologists, and perinatologists.

Learning to segment fetal brain tissue from noisy annotations

Automatic fetal brain tissue segmentation can enhance the quantitative assessment of brain development at this critical stage. Deep learning methods represent the state of the art in medical image segmentation and have also achieved impressive results in brain segmentation. However, effective training of a deep learning model to perform this task requires a large number of training images to represent the rapid development of the transient fetal brain structures. On the other hand, manual multi-label segmentation of a large number of 3D images is prohibitive. To address this challenge, we segmented 272 training images, covering 19-39 gestational weeks, using an automatic multi-atlas segmentation strategy based on deformable registration and probabilistic atlas fusion, and manually corrected large errors in those segmentations. Since this process generated a large training dataset with noisy segmentations, we developed a novel label smoothing procedure and a loss function to train a deep learning model with smoothed noisy segmentations. Our proposed methods properly account for the uncertainty in tissue boundaries. We evaluated our method on 23 manually-segmented test images of a separate set of fetuses. Results show that our method achieves an average Dice similarity coefficient of 0.893 and 0.916 for the transient structures of younger and older fetuses, respectively. Our method generated results that were significantly more accurate than several state-of-the-art methods including nnU-Net that achieved the closest results to our method. Our trained model can serve as a valuable tool to enhance the accuracy and reproducibility of fetal brain analysis in MRI.

Preliminary Study on Quantitative Assessment of the Fetal Brain Using MOLLI T1 Mapping Sequence

BACKGROUND

Prenatal quantitative evaluation of myelin is important. However, few techniques are suitable for the quantitative evaluation of fetal myelination.

PURPOSE

To optimize a modified Look-Locker inversion recovery (MOLLI) T1 mapping sequence for fetal brain development study.

STUDY TYPE

Prospective observational preliminary cohort study.

POPULATION

A total of 71 women with normal fetuses divided into mid-pregnancy (gestational age 24-28 weeks, N = 25) and late pregnancy (gestational age > 28 weeks, N = 46) groups.

FIELD STRENGTH/SEQUENCE

A 3 T/MOLLI sequence.

ASSESSMENT

T1 values were measured in pedunculus cerebri, basal ganglia, thalamus, posterior limb of the internal capsule, temporal white matter, occipital white matter, frontal white matter, and parietal white matter by two radiologists (11 and 16 years of experience, respectively).

STATISTICAL TESTS

The Kruskal-Wallis test was used for reginal comparison. For each region of interest (ROI), differences in T1 values between the mid and late pregnancy groups were assessed by the Mann Whitney U test. Pearson correlation coefficients (r) were used to evaluate the correlations between T1 values and gestational age for each ROI. Intraobserver and interobserver agreement was determined by the intraclass correlation coefficient (ICC). A P value <0.05 was considered statistically significant.

RESULTS

Interobserver and intraobserver agreements of T1 were good for all ROIs (all ICCs > 0.700). There were significant differences in T1 values between lobal white matter and deep regions, respectively. Significant T1 values differences were found between middle and late pregnancy groups in pedunculus cerebri, basal ganglion, thalamus, posterior limb of the internal capsule, temporal, and occipital white matter. The T1 values showed significantly negative correlations with gestational weeks in pedunculus cerebri (r = -0.80), basal ganglion (r = -0.60), thalamus (r = -0.68), and posterior limb of the internal capsule (r = -0.77).

DATA CONCLUSION

The T1 values of fetal brain may be assessed using the MOLLI sequence and may reflect the myelination.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 2.

Outcome of Agenesis of the Corpus Callosum Diagnosed by Fetal MRI

BACKGROUND

Fetal magnetic resonance imaging (MRI) is increasingly utilized for prenatal diagnosis of agenesis of the corpus callosum (ACC). This study aimed to (1) describe cases of ACC diagnosed by fetal MRI, (2) determine the frequency of postnatal confirmation by MRI, and (3) understand postnatal outcomes of infants with ACC.

METHODS

Maternal records from Children's National Hospital between January 2012 and June 2019 with a prenatal neurological consultation, fetal MRI, and ACC on imaging were included. Maternal, prenatal, and postnatal infant data were collected. Each case was categorized as complete or partial ACC and isolated or complex ACC by fetal MRI and group comparisons of outcomes were analyzed.

RESULTS

A total of 127 maternal-fetal dyads with ACC were categorized into 45 isolated-complete, 17 isolated-partial, 46 complex-complete, and 19 complex-partial ACC. Of 75 live births, 72 had postnatal evaluations. In 43 of 59 (73%) cases with postnatal neuroimaging, prenatal ACC subcategory was confirmed. Children with isolated or complex and with partial or complete ACC had similar rates of developmental delays and epilepsy. Complex ACC cases had worse outcomes than isolated ACC, with complex ACC having more postnatal dysmorphisms and abnormal feeding and vision compared with isolated ACC. Similar neurodevelopmental outcomes were seen for partial and complete ACC.

CONCLUSIONS

Children with isolated or complex ACC and with partial or complete ACC have a range of neurodevelopmental outcomes. Fetal and postnatal brain MRI is a valuable tool to understand differences of the corpus callosum that can guide genetic testing, prenatal counseling, and postnatal care.

Bilateral Coronal Synostosis and Mega Cisterna Magna: A Case Report

Craniosynostosis is often associated with raised intracranial pressure (ICP), especially when multiple sutures are involved. In this report, we discuss an unusual association in a patient with craniosynostosis. We report a case of a two-year-old Caucasian male with bilateral coronal synostosis (BCS) who was found to have a concomitant mega cisterna magna (MCM). Although counterintuitive, even in the presence of craniosynostosis, patients with this finding can also have intracranial CSF fluid collections such as the MCM reported here. We hope this report will enhance our understanding of some similar cases that are equivocal regarding raised ICP.

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.

Role of prenatal magnetic resonance imaging in fetuses with isolated anomalies of corpus callosum: multinational study

OBJECTIVE

To assess the performance of fetal magnetic resonance imaging (MRI) in detecting associated anomalies in fetuses diagnosed with isolated corpus callosal (CC) anomaly on multiplanar ultrasound evaluation of the fetal brain (neurosonography).

METHODS

This was a multicenter, retrospective cohort study involving 14 fetal medicine centers in Italy, UK, Portugal, Canada, Austria and Spain. Inclusion criteria were fetuses with an apparently isolated CC anomaly, defined as an anomaly of the CC and no other additional central nervous system (CNS) or extra-CNS abnormality detected on expert ultrasound, including multiplanar neurosonography; normal karyotype; maternal age ≥ 18 years; and gestational age at diagnosis ≥ 18 weeks. The primary outcome was the rate of additional CNS abnormalities detected exclusively on fetal MRI within 2 weeks following neurosonography. The secondary outcomes were the rate of additional abnormalities according to the type of CC abnormality (complete (cACC) or partial (pACC) agenesis of the CC) and the rate of additional anomalies detected only on postnatal imaging or at postmortem examination.

RESULTS

A total of 269 fetuses with a sonographic prenatal diagnosis of apparently isolated CC anomalies (207 with cACC and 62 with pACC) were included in the analysis. Additional structural anomalies of the CNS were detected exclusively on prenatal MRI in 11.2% (30/269) of cases, with malformations of cortical development representing the most common type of anomaly. When stratifying the analysis according to the type of CC anomaly, the rate of associated anomalies detected exclusively on MRI was 11.6% (24/207) in cACC cases and 9.7% (6/62) in pACC cases. On multivariate logistic regression analysis, only maternal body mass index was associated independently with the likelihood of detecting associated anomalies on MRI (odds ratio, 1.07 (95% CI, 1.01-1.14); P = 0.03). Associated anomalies were detected exclusively after delivery and were missed on both types of prenatal imaging in 3.9% (8/205) of fetuses with prenatal diagnosis of isolated anomaly of the CC.

CONCLUSION

In fetuses with isolated anomaly of the CC diagnosed on antenatal neurosonography, MRI can identify a small proportion of additional anomalies, mainly malformations of cortical development, which are not detected on ultrasound. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Mapping fetal brain development based on automated segmentation and 4D brain atlasing

Fetal brain MRI has become an important tool for in utero assessment of brain development and disorders. However, quantitative analysis of fetal brain MRI remains difficult, partially due to the limited tools for automated preprocessing and the lack of normative brain templates. In this paper, we proposed an automated pipeline for fetal brain extraction, super-resolution reconstruction, and fetal brain atlasing to quantitatively map in utero fetal brain development during mid-to-late gestation in a Chinese population. First, we designed a U-net convolutional neural network for automated fetal brain extraction, which achieved an average accuracy of 97%. We then generated a developing fetal brain atlas, using an iterative linear and nonlinear registration approach. Based on the 4D spatiotemporal atlas, we quantified the morphological development of the fetal brain between 23 and 36 weeks of gestation. The proposed pipeline enabled the fully automated volumetric reconstruction for clinically available fetal brain MRI data, and the 4D fetal brain atlas provided normative templates for the quantitative characterization of fetal brain development, especially in the Chinese population.

Brain fetal neuroradiology: a beginner's guide

The importance of fetal magnetic resonance imaging (MRI) in the prenatal diagnosis of central nervous system (CNS) anomalies is rapidly increasing. Fetal MRI represents a third level examination usually performed, as early as 18-20 weeks of gestational age, when a second level (expert) neuro-ultrasonography (US) evaluation raises the suspicion of a CNS anomaly or when a genetic disorder is known. Compared to the US, MRI has the advantage to allow a better visualization and characterization of brain structures so to detect anomalies not visible in the US, thus resulting in relevant implications for parent counselling and pregnancy management. Moreover, the improvement of MRI technologies permits to obtain ultrafast sequences, which minimize the drawback of movement artifacts, and to perform advanced studies. This review aims at providing a practical guide for trainees and fellows who are approaching fetal MRI. In the first part, we provide information about indications, safety and protocols based on the state-of-the-art sequences, with a mention on the innovations related to the use of a 3T scanner. The second part is focused on the normal development of the human fetal brain related to its MR appearance, whose knowledge is essential to detect possible abnormalities. The last section briefly describes the most frequent abnormalities in the fetal brain and spine as depicted by MRI.

Evaluation of the development of the posterior fossa in normal Chinese fetuses by using magnetic resonance imaging

The posterior fossa is an important brain structure containing the cerebellum, cerebral ventricle, and cistern. Early evaluation of the cerebellar structure and function may be valuable for early detection of fetal deformities. At present, no normal value for the fetal posterior fossa has been established yet. This study is aimed to investigate the development of the posterior fossa in normal Chinese fetuses by using magnetic resonance imaging (MRI).Pregnant women who need MRI scan were enrolled in our Hospital between January 2012 and December 2014. The fetal supero-inferior diameter (SID), anterio-posterior diameter (APD), cerebellar vermis area, cerebellar width (CW), cerebellar volume (CV), superior cerebellar cistern width, and cerebellomedullary cistern width were measured using MRI. Pearson's correlation analysis was used to detect the relationship between those parameters and gestational age. A regression analysis was performed for all parameters.A total of 92 participants were retrospectively enrolled finally. The results indicated SID, APD, cerebellar vermis area, CW, and CV were positively associated with gestational age, while no significant correlation was found between the superior cerebellar cistern width and cerebellomedullary cistern width and gestational age. Each equation was established.Our study demonstrated that MRI has the advantages over ultrasound imaging for prenatal evaluation of the fetal posterior fossa with multiple views. Normal value of the posterior fossa of Chinese fetuses was established in this study.

Developmental dynamics of the periventricular parietal crossroads of growing cortical pathways in the fetal brain - In vivo fetal MRI with histological correlation

The periventricular crossroads have been described as transient structures of the fetal brain where major systems of developing fibers intersect. The triangular parietal crossroad constitutes one major crossroad region. By combining in vivo and post-mortem fetal MRI with histological and immunohistochemical methods, we aimed to characterize these structures. Data from 529 in vivo and 66 post-mortem MRI examinations of fetal brains between gestational weeks (GW) 18-39 were retrospectively reviewed. In each fetus, the area adjacent to the trigone of the lateral ventricles at the exit of the posterior limb of the internal capsule (PLIC) was assessed with respect to signal intensity, size, and shape on T2-weighted images. In addition, by using in vivo diffusion tensor imaging (DTI), the main fiber pathways that intersect in these areas were identified. In order to explain the in vivo features of the parietal crossroads (signal intensity and developmental profile), we analyzed 23 post-mortem fetal human brains, between 16 and ​40 GW of age, processed by histological and immunohistochemical methods. The parietal crossroads were triangular-shaped areas with the base in the continuity of the PLIC, adjacent to the germinal matrix and the trigone of the lateral ventricles, with the tip pointing toward the subplate. These areas appeared hyperintense to the subplate, and corresponded to a convergence zone of the developing external capsule, the PLIC, and the fronto-occipital association fibers. They were best detected between GW 25-26, and, at term, they became isointense to the adjacent structures. The immunohistochemical results showed a distinct cellular, fibrillar, and extracellular matrix arrangement in the parietal crossroads, depending on the stage of development, which influenced the MRI features. The parietal crossroads are transient, but important structures in white matter maturation and their damage may be indicative of a poor prognosis for a fetus with regard to neurological development. In addition, impairment of this region may explain the complex neurodevelopmental deficits in preterm infants with periventricular hypoxic/ischemic or inflammatory lesions.

Preliminary Experience Using Motion Compensated CINE Magnetic Resonance Imaging to Visualise Fetal Congenital Heart Disease

BACKGROUND

Recent advances in cardiovascular magnetic resonance (CMR) imaging have facilitated CINE imaging of the fetal heart. In this work, a preliminary investigation of the utility of multislice CINE CMR for assessing fetal congenital heart disease is performed and compared with echocardiography.

METHODS AND RESULTS

Multislice CINE CMR and echocardiography images were acquired in 25 pregnant women wherein the fetus had a suspected congenital heart defect based on routine obstetric ultrasound. Pathognomonic images were identified for each subject for qualitative comparison of CMR and echocardiography. Quantitative comparison of CMR and echocardiography was then performed by 2 reviewers using a binary scoring of 9 fetal cardiac anatomic features (identifiable/not-identifiable). Pathognomonic images demonstrated the ability of CMR to visualize a variety of congenital heart defects. Overall CMR was able to identify the majority of the 9 assessed fetal cardiac anatomic features (reviewer 1, 7.1±2.1; reviewer 2, 6.7±2.3). Although both reviewers identified more anatomic features with echocardiography (reviewer 1, 7.8±2.3; reviewer 2, 7.5±2.4; P=0.01), combining information from both modalities enabled identification of additional anatomic features across subjects (reviewer 1, 8.4±1.3; reviewer 2, 8.4±1.2). The primary limiting factor for CMR was inadequate coverage of the fetal cardiac anatomy or noncontiguous slices because of gross fetal movement.

CONCLUSIONS

CINE CMR enables visualization of fetal congenital heart disease. This work demonstrates the potential of CMR for diagnosing congenital heart disease in utero in conjunction with echocardiography during late gestation.

Volume growth trend and correlation of atrial diameter with lateral ventricular volume in normal fetus and fetus with ventriculomegaly: A STROBE compliant article

To explore the growth trend of fetal lateral ventricular volume, for understanding the relationship between atrial diameter (AD) and volume in normal fetus and fetus with ventriculomegaly.Overall, 97 sequential fetal head magnetic resonance imaging scans were performed; these pertained to 50 fetuses with normal lateral ventricles [normal group; gestational age (GA): 24-38 weeks] and 47 fetuses with ventriculomegaly (VM) (VM group; GA: 24-37 weeks). The left, right, and total lateral ventricular volume were measured using 3-dimensional magnetic resonance hydrography (MRH). Correlation coefficient (r) was calculated to assess the relationships of measurements. Lineal regression analysis was used to assess correlation of AD and GA with volume. Between-group differences in terms of AD and volume were assessed using t test.Significant linear growth was observed in the total lateral ventricular volume compared with GA in the normal group with a relative growth rate of 2.87% per week (P <.001). Significant linear relationship between AD and volume was observed, and a significant equation was acquired in the normal group and VM groups, respectively, using the simple linear regression model: left volume = 0.438 * normal left diameter (NLD) + 1.359; right volume = 0.493 * normal right diameter (NRD) + 1.012; left volume = 0.959 * left diameter in VM (VLD) - 2.074; right volume = 0.799 * right diameter in VM (VRD) - 0.443. A significant equation was obtained in the normal group and the VM group, using the multiple linear regression model: Total volume (mL) = 0.396 * NLD + 0.410 * NRD + 3.101; and total volume = 0.989 * VLD + 0.834 * VRD - 3.141, respectively. In terms of AD and volume, the left lateral ventricle was significantly larger than the right side in both groups. The volume of lateral ventricle in AD ≥10 mm group was larger than that in the AD <10 mm group. The total volume in the VM group was significantly larger than that in the normal group.The total lateral ventricular volume increased with GA. AD can be used to evaluate the fetal ventricular volume.

A Dedicated 36-Channel Receive Array for Fetal MRI at 3T

Due to a lack of fetal imaging coils, the standard commercial abdominal coil is often used for fetal imaging, the performance of which is limited by its insufficient coverage, element number, and Signal-to-noise ratio (SNR). In this paper, a dedicated 36-channel coil array, of which size can best fit the body sizes of pregnancy gestation from 20 to 37+ weeks, was designed for fetal imaging at 3T. SNR with full phase encoding and G-factor denoted as noise amplification for parallel imaging were quantitatively evaluated by phantom studies. Compared with a commercial abdominal coil array, the proposed 36-channel fetal array provides not only SNR improvements in full phase encoding (with 10% in the region where the whole fetal body was located, and up to 40% in the edge region where the fetal brain and heart may appear) but also an augmented parallel imaging capability and remarkable SNR improvements at high acceleration factors.

Fetal cerebellar disorders

The embryologic development of the cerebellum extends over a long time period, thus making it vulnerable to a broad spectrum of malformations and disruptions. Knowledge of the main steps of fetal posterior fossa development; the normal imaging patterns at different stages of embryogenesis; the large spectrum of cerebellar malformations; and their clinical presentations enables diagnosis and precise counseling of parents. Sonography is the most important imaging method for the screening of cerebellar malformations since it is noninvasive, widely available, and safe for both mother and child. The ultrasonographic approach for the evaluation of the fetal posterior fossa is based on the classic transabdominal visualization of axial planes with addition when indicated of a more comprehensive, multiplanar transvaginal or transfundal approach, including coronal and sagittal imaging planes. Fetal magnetic resonance imaging (MRI) has become an adjunct to prenatal ultrasound since the 1980s. Good-quality images have been obtained thanks to the implementation of fast and ultrafast MRI sequences. Fetal MRI has higher-contrast resolution than prenatal sonography and may contribute to the differentiation of normal from abnormal tissue. Both prenatal neurosonography and fetal MRI enable accurate prenatal diagnosis of most posterior fossa anomalies.

Different information by MRI compare to ultrasound in fetal intracranial space occupying lesions

PURPOSE

The purpose of this study was to evaluate the value of prenatal magnetic resonance imaging (MRI) in characterizing fetal intracranial space occupying lesions in comparison to prenatal ultrasound.

METHODS

This retrospective study included 50 fetuses (mean age 26 years, mean gestational weeks 31 + 1 GW) with intracranial space occupying lesions, suspected by prenatal screening ultrasound. T2-weighted, T1-weighted, SSFP, and diffusion-weighted sequences of the fetal brain were obtained on a 1.5 T unit. Pathology (n = 5), postmortem MRI (n = 3), or postnatal US (n = 42) was available as standard of reference.

RESULTS

The fetal MRI provided correct diagnosis in 49 cases (98%), while 35 (70%) by ultrasound, and MRI failed in 1 case (2%), while ultrasound failed in 15 cases (30%). Fetal MR and ultrasound were concordant in 35 of 50 cases (70%), completely discordant in 4 (8%), and partially discordant in 11 (22%) cases.

CONCLUSIONS

MRI could provide detailed information about the minor lesions, such as focal hemorrhage and periventricular nodules. Meanwhile, it could provide whole view of the lesion in order to delineate the surrounding anatomical structure. But there are still some limitations of its soft-tissue resolution in a case with teratoma; more effort is needed to improve the sequences.

Magnetic resonance imaging based correlation analysis between calcarine sulcus development and isolated fetal ventriculomegaly

Fetal ventriculomegaly development leads to neurological, motor, and/or cognitive impairment, and is presently diagnosed based on the width of the atrium in the lateral ventricle. But in this study, we have tried to assess the relationship between the development of calcarine sulcus and width of fetal lateral ventricles, to assess if calcarine sulcus can also be used for fetal ventriculomegaly diagnosis. We conducted a retrospective analysis of the magnetic resonance imaging (MRI) data from 45 subjects with isolated mild fetal ventriculomegaly (IMVM). The calcarine sulcus development was divided into three categories based on the depth; Grade 1 (undeveloped), Grade 2 (underdeveloped), and Grade 3 (fully developed), and its correlation with fetal ventriculomegaly was analyzed based on Spearman's partial rank correlation test. Based on this analysis, the width of left and right lateral ventricles showed significant downward trend with the calcarine sulcus maturation [undeveloped (Left 13.88 ± 2.70 mm, Right 14.27 ± 3.13 mm) → underdeveloped (Left 12.95 ± 1.93 mm, Right 11.93 ± 2.24 mm) → fully developed (Left 11.06 ± 2.10 mm, Right 10.42 ± 2.10 mm)] (F_Left  = 5.12, P = 0.01; F_Right  = 10.72, P = 1.73 × 10^-4 ). In addition, significant correlations were also observed between the width of the lateral ventricles and the maturity of the calcarine sulcus (Spearman's rank correlation coefficient; -0.47 for the left lateral ventricles and -0.56 for the right, both P < 0.001). Overall, our data indicated a negative correlation between the fetal morphological development of calcarine sulcus and the width of lateral ventricles in subjects having isolated fetal ventriculomegaly.

Findings and differential diagnosis of fetal intracranial haemorrhage and fetal ischaemic brain injury: what is the role of fetal MRI?

Ventriculomegaly (VM) is a non-specific finding on fetal imaging. Identification of the specific aetiology is important, as it affects prognosis and may even change the course of current or future pregnancies. In this review, we will focus on the application of fetal MRI to demonstrate intracranial haemorrhage and ischaemic brain injury as opposed to other causes of VM. MRI is able to identify the specific aetiology of VM with much more sensitivity and specificity than ultrasound and should be considered whenever VM is identified on obstetric ultrasound. Advances in both fetal and neonatal MRI have the potential to shed further light on mechanisms of brain injury and the impact of chronic hypoxia; such information may guide future interventions.

Prenatal diagnosis of Chudley-McCullough syndrome

Chudley-McCullough syndrome (CMS) is an autosomal-recessive disorder characterized by a complex brain malformation and profound congenital sensorineural hearing loss. Postnatal brain imaging findings include ventriculomegaly, partial agenesis of corpus callosum, inferior cerebellar dysplasia, arachnoid cysts, and malformations of cortical development including frontal subcortical heterotopia and polymicrogyria. Prenatal diagnosis of CMS is important due to the markedly less severe neurodevelopmental prognosis compared to disorders with similar brain imaging findings. We report prenatal imaging features that help distinguish CMS from other disorders, including slit-like frontal horns, agenesis of the corpus callosum, frontal subcortical heterotopia, arachnoid cysts, and cerebellar dysplasia. © 2016 Wiley Periodicals, Inc.

Pränataldiagnostik bei fetaler Mikrozephalie

Diese Übersichtsarbeit behandelt die Mikrozephalie (MZ) aus der Perspektive der pränatalen Diagnostik. Eine MZ wird bei einem Kopfumfang unter der dritten Standardabweichung für das Gestationsalter vermutet. Diese Verdachtsdiagnose kann aus einem falschen Gestationsalter oder einer falsche Messung resultieren oder infolge einer Reihe häufiger Ätiologien wie offene Spina bifida, Enzephalozele, Holoprosenzephalie, Infektion, Aneuploidie, seltener auch Ursachen wie einer primären oder syndromalen MZ entstehen. Typische Ultraschallzeichen einer fetalen MZ sind die flache Stirn, der kleine Frontallappen, das reduzierte Gyrierungsmuster mit einem kurzen Balken, eine Pseudo-Kraniosynostose, ein dilatierter Subarachnoidalraum und oft eine Diskrepanz zwischen Kopf- und Bauchumfang. Mitunter kann eine schwere MZ schon in der Mitte der Schwangerschaft entdeckt werden, aber die meisten Formen fallen erst im III. Trimenon bzw. nach der Geburt auf. Die diagnostische Abklärung sollte auch das Angebot genetischer Untersuchungen einschließen, um monogen vererbte Formen mit hohem Wiederholungsrisiko z. B. bei autosomal-rezessiver Vererbung zu identifizieren. Die Arbeit diskutiert pränatalmedizinische und genetisch-diagnostische Abklärungsschritte bei fetaler MZ, die in Kombination mit den neuen genetischen Untersuchungstechniken hoffentlich in Zukunft zu einer höheren Aufklärungsrate führen werden.