Magnetic resonance imaging and the detection of fetal brain anomalies, injury, and physiologic adaptations

PURPOSE OF REVIEW: Magnetic resonance imaging is playing an increasingly prominent role in depicting brain maturation, especially gyral formation that follows a temporospatial pattern, and in detecting developmental abnormalities of the cortex and other brain sectors. Knowledge of the technical advantages and limitations of in-utero magnetic resonance imaging techniques, relative to those of the postnatal period, is essential to optimize magnetic resonance sequences for early diagnosis. This includes an understanding of the changes in both brain anatomy and magnetic resonance signals that occur with an increase in gestational age. RECENT FINDINGS: Magnetic resonance imaging has evolved has an important adjunct in the diagnosis of brain malformations, particularly in the late-second or third trimester. Noxious conditions elicit more of a chronic rather than acute response in the fetal brain, which differs from that observed postnatally. Clinical applications of proton magnetic resonance spectroscopy may help elucidate fetal brain maturation and its abnormalities from a metabolic point of view. SUMMARY: Indications for fetal brain magnetic resonance imaging have increased because of improvements in magnetic resonance techniques and the ability to detect subtle changes within the cerebral parenchyma, especially in fetuses at increased risk of brain damage.     

Perinatal management of fetal malformations amenable to surgical correction

Advances in prenatal imaging modalities such as ultrasound and magnetic resonance imaging have permitted the more frequent and accurate diagnosis of congenital malformations. Fetal surgical intervention has been reserved for those malformations that lead to fetal demise or are life-threatening in the neonatal period. We review the current indications for intervention in fetuses diagnosed with congenital lung lesions, congenital diaphragmatic hernia, sacrococcygeal teratoma, and obstructing airway lesions. A discussion of the recent interest in the fetal repair of severe myelomeningocele is also included.     

Comparison of ultrasound and magnetic resonance imaging in 100 singleton pregnancies with suspected brain abnormalities

OBJECTIVE: To compare the diagnostic accuracy of the current reference standard-ultrasound with in utero magnetic resonance imaging, in a selected group of patients. DESIGN: Prospective study. SETTING: Five fetal maternal tertiary referral centres and an academic radiology unit. SAMPLE: One hundred cases of fetuses with central nervous system abnormalities where there has been diagnostic difficulties on ultrasound. In 48 cases the women were less than 24 weeks of gestation and in 52 cases later in pregnancy. METHODS: All women were imaged on a 1.5 T clinical system using a single shot fast spin echo technique. The results of antenatal ultrasound and in utero magnetic resonance were compared. MAIN OUTCOME MEASURES: The definitive diagnosis was made either at autopsy or by postmortem magnetic resonance imaging, in cases that went to termination of pregnancy, or a combination of postnatal imaging and clinical follow up in the others. RESULTS: In 52 of cases, ultrasound and magnetic resonance gave identical results and in a further 12, magnetic resonance provided extra information that was judged not to have had direct effects on management. In 35 of cases, magnetic resonance either changed the diagnosis (29) or gave extra information that could have altered management (6). In 11 of the 30 cases where magnetic resonance changed the diagnosis, the brain was described as normal on magnetic resonance. CONCLUSIONS: In utero magnetic resonance imaging is a powerful tool in investigating fetal brain abnormalities. Our results suggest that in selected cases of brain abnormalities, detected by ultrasound, antenatal magnetic resonance may provide additional, clinically useful information that may alter management.     

Prenatal diagnosis of arachnoid cysts

Arachnoid cysts are a rare central nervous system malformation, representing only 1% of all intracranial masses in newborns. Primary (congenital) arachnoid cysts are benign accumulation of clear fluid between the dura and the brain substance throughout the cerebrospinal axis in relation to the arachnoid membrane and do not communicate with the subarachnoid space. Secondary (acquired) arachnoid cysts result from hemorrhage, trauma, and infection and usually communicate with the subarachnoid space. The common locations of arachnoid cysts are the surface of the brain at the level of main brain fissures, such as sylvian, rolandic and interhemispheric fissures, sella turcica, the anterior cranial fossa, and the middle cranial fossa. Arachnoid cysts may be associated with ventriculomegaly and dysgenesis of corpus callosum. Prenatal ultrasound and magnetic resonance imaging have led to the increased diagnosis of fetal arachnoid cysts. This article provides a thorough review of fetal arachnoid cysts, including prenatal diagnosis, differential diagnosis and associated chromosomal abnormalities, as well as comprehensive illustrations of perinatal imaging findings of fetal arachnoid cysts. Prenatal diagnosis of intracranial hypoechoic lesions should include a differential diagnosis of arachnoid cysts and prompt genetic investigations.     

Phenotype to genotype characterization by array-comparative genomic hydridization (a-CGH) in case of fetal malformations: A systematic review

The aim of the current review is to report a-CGH abnormalities identified in fetuses with prenatally diagnosed fetal malformations in whom a normal karyotype was diagnosed with conventional cytogenetic analysis.A systematic electronic search of databases (PubMed/Medline, EMBASE/SCOPUS) has been conducted from inception to May, 2017. Bibliographic analysis has been performed according to PRISMA statement for review. The following keywords were used: ‘array-CGH’ and ‘fetal malformations” and “prenatal diagnosis”; alternatively, “microarray”, “oligonucleotide array”, “molecular biology”, “antenatal diagnostics”, “fetal diagnostics”, “congenital malformations” and “ultrasound” were used to capture both “a-CGH” and “prenatal”.One-hundred and twelve fetuses with prenatally diagnosed fetal malformations with normal karyotyping and a-CGH abnormalities detected are described. Single or multiple microarray abnormalities diagnosed have been classified in relation to different organ/system affected. The most frequent a-CGH abnormalities were detected in cases of congenital heart diseases (CDHs), multiple malformations and central nervous system (CNS) malformations. Maternal or paternal carrier-state was seen in 19.64% (22/112), of cases while the number of reported de novo mutations accounted for 46.42% (52/112) of all CNVs microarray abnormalities. Array-comparative genomic hydridization (a-CGH) may become an integral and complemantary genetic testing when fetal malformations are detected prenatally in fetuses with normal cytogenetic karyotype. In addition, a-CGH enables the identification of CNVs and VOUS and improves the calculation of recurrent risk and the genetic counseling.     

Fast-scan magnetic resonance imaging of fetal anomalies.

OBJECTIVE--To identify those congenital fetal anomalies, previously identified by ultrasound scanning, in which fast-scan magnetic resonance imaging (F-SMRI) would give additional information for the perinatal management of the infants. DESIGN--Observational clinical study. SETTING--Hospital Department of Obstetrics and Gynaecology/Resonance Research Centre. SUBJECTS--Seven women carrying eight fetuses in whom congenital abnormalities had been identified using ultrasound scans. The duration of the pregnancies was 28 to 39 weeks gestation. INTERVENTIONS--Fast-scan magnetic resonance imaging at between 28 and 39 weeks gestation. MAIN OUTCOME MEASURES--Identification of fetal abnormalities. RESULTS AND CONCLUSIONS--F-SMRI was of limited value in the diagnosis of further assessment of fetuses with abnormalities of accumulation of tissue fluid. Renal anomalies were poorly identified unless associated with cystic formation of the kidney. Further study is required in the imaging of fetal central nervous system anomalies. Until echoplanar imaging is more widely available, MRI does not contribute to the diagnosis of cardiac anomalies. F-SMRI appears to be most useful in the diagnosis and management of soft tissue gastro intestinal abnormalities.     

Second-opinion magnetic resonance imaging for suspected fetal central nervous system abnormalities

OBJECTIVE: The purpose of this study was to evaluate the relationship of magnetic resonance imaging and gestational age in the setting of fetuses with suspected abnormalities of the central nervous system that were detected by ultrasound scanning. STUDY DESIGN: Multiplanar magnetic resonance studies were performed in fetuses with suspected central nervous system abnormalities on ultrasound scanning. Magnetic resonance imaging was evaluated for its ability to provide additional information, change the diagnosis, or impact obstetric treatment. Patients were grouped by gestational age at the time of magnetic resonance imaging. RESULTS: Magnetic resonance imaging provided additional information in 46 of 72 pregnancies (64%), changed the diagnosis in 20 of 72 pregnancies (28%), and potentially altered the timing or mode of delivery in 8 of 72 pregnancies (11%). Additional information increased with increasing gestational age groups (P =.03). CONCLUSION: Magnetic resonance imaging provided additional information in two thirds of the fetuses with central nervous system abnormalities, which was significantly increased with increasing gestation. Antenatal treatment was influenced by magnetic resonance imaging in 11% of the cases.     

Prenatal diagnosis of abdominal lymphatic malformations

Abdominal lymphatic malformations (LM) are rare congenital malformations of the lymphatic system, representing only 2% of all LM in newborns. They may arise from intra-abdominal solid organs (such as the liver, pancreas, kidneys, spleen, adrenal glands, and gastrointestinal tract), mesentery, omentum, and retroperitoneum. Mesenteric LM are the most commonly seen, with retroperitoneal LM being the second most common. Fetal abdominal LM could be associated with karyotypic or other abnormalities, including skin edema, hydrops fetalis, and polyhydramnios, and prenatal diagnosis and perinatal counseling for these LM are important. Prenatal ultrasound (US) and magnetic resonance imaging (MRI) have led to an increased diagnosis of abdominal LM and improved monitoring and intervention postnatally. This article provides an overview of fetal abdominal LM, including the prenatal diagnoses, differential diagnoses, comprehensive illustrations of the imaging findings, treatments, and fetal outcomes.     

Magnetic resonance imaging in human pregnancy

Magnetic resonance imaging is a new noninvasive diagnostic technique that involves no ionizing radiation, has no known significant adverse biologic effects, and produces high resolution cross-sectional body images. When compared with sonography and x-ray computed axial tomography, magnetic resonance imaging may have several advantages. To investigate its clinical role in obstetrics, magnetic resonance imaging was used to examine 11 women with abnormal pregnancies. Prior ultrasound examination showed abnormal appearing fetuses in five, abnormalities of the amnionic fluid volume in five, and one each with a large adnexal mass and a molar pregnancy. Examples of images obtained from these women are presented and described. Maternal anatomy was well visualized in all women studied. Based on the preliminary experience, the authors believe that magnetic resonance imaging will be a useful adjunct for diagnostic visualization of normal and abnormal maternal anatomy. Detailed fetal imaging was also possible, and it is anticipated that magnetic resonance imaging will prove useful for fetal evaluation, especially fetal intracranial anatomy and fetal anatomy in pregnancies complicated by oligohydramnios. Because fetal subcutaneous fat is prominently depicted with magnetic resonance imaging, this technology may be useful for assessment of fetal nutritional status.     

Fetal magnetic resonance imaging in prenatal diagnosis of central nervous system abnormalities: 3-year experience

Objective: To evaluate the comparative merits of ultrasound and fetal magnetic resonance imaging (MRI) in the correct antenatal diagnosis of suspected central nervous system abnormalities. Methods: A retrospective review of 27 consecutive pregnancies referred for fetal MRI for suspected central nervous system abnormalities between July 1998 and July 2001. Women were referred for the MRI examination when further anatomical and/or pathological clarification of the ultrasound scan findings was needed. Antenatal ultrasound scan and MRI were reviewed in relation to the findings on postpartum investigations. Results: Data were complete for 26 pregnancies. The median gestational age at the time of the ultrasound examination was 26 weeks (95% CI 24 weeks 2 days to 28 weeks 1 day). The median gestational age at the time of magnetic resonance imaging was 27 weeks' gestation (95% CI 26 weeks 1 day to 29 weeks 2 days). Eight fetuses had associated skeletal, renal and/or cardiac abnormalities previously noted on ultrasound examination. MRI confirmed the ultrasound diagnosis in 15/26 cases (58%). It changed the diagnosis to the correct one in 7/26 (27%) and misdiagnosed four cases (15%). Three of the four cases that were misdiagnosed on MRI occurred in the first 18 months of our 36-month experience. Conclusion: Ultrasound remains the primary imaging modality for prenatal diagnosis. Fetal MRI appears to be a useful adjunct to ultrasound to confirm or exclude certain abnormalities; this will consequently help in the counselling of parents and assist in planning further management. However, like any imaging technique, the sensitivity and specificity of the test are likely to improve with experience.     

Usefulness of additional fetal magnetic resonance imaging in the prenatal diagnosis of congenital abnormalities

Objective

Our aim was to compare the value of fetal magnetic resonance imaging (MRI) with detailed ultrasound in the prenatal diagnosis of congenital abnormalities.

Materials and methods

This retrospective study reviewed the medical records of pregnant women and their neonates who, after ultrasound, were suspected to have congenital abnormalities. They then underwent a detailed ultrasound examination and a fetal MRI in our institutions. Fetal MRI was performed in 81 cases. Each prenatal presumptive diagnosis, based on detailed ultrasound examination and fetal MRI, was compared with the postnatal confirmed diagnosis. In 58 cases, the data collected were confirmed by the postnatal diagnosis.

Results

Supplemental information from fetal MRI was useful in 17 of the 22 cases involving the central nervous system (CNS), two of two cases involving the thorax, nine of nine cases involving the genitourinary system, two of eight cases involving the gastrointestinal system, and ten of ten cases involving complex malformations. Fetal MRI did not provide significantly useful information or facilitate a more accurate diagnosis except for CNS abnormalities.

Conclusion

Fetal MRI was not superior to an ultrasound examination in the prenatal detection of congenital abnormalities. A detailed ultrasound examination performed by experienced obstetricians had satisfactory accuracy in the diagnosis of fetal abnormalities compared with fetal MRI. Fetal MRI might be useful in appropriate cases in Korea. Greater effort is required to increase the ultrasound knowledge and skill of competent obstetricians.     

Use of fetal magnetic resonance imaging in patients electing termination of pregnancy by dilation and evacuation

OBJECTIVE: The purpose of this study was to determine whether magnetic resonance imaging of the fetal brain before dilation and evacuation enhances diagnosis when equivocal ultrasound findings and disrupted autopsy specimens exist. STUDY DESIGN: Patients with equivocal fetal brain abnormalities on ultrasound examination who were considering termination of pregnancy were evaluated retrospectively. Abdominal and pelvic magnetic resonance imaging was performed for further evaluation, and orthogonal fetal brain images were obtained. A multidisciplinary team reviewed all cases and discussed the findings, possible causes, and recurrence risks with each patient. RESULTS: Seven patients with fetal brain anomalies underwent magnetic resonance imaging before dilation and evacuation. Magnetic resonance imaging diagnoses included intracranial hemorrhages, semilobar holoprosencephaly, intracranial teratoma, multiple cerebral infarcts, and unilateral cerebellar hypoplasia. In all cases, magnetic resonance imaging provided valuable information and helped distinguish possible genetic syndromes from likely sporadic disorders of brain development. CONCLUSION: Magnetic resonance imaging can provide insight into diagnosis, cause, and recurrence risks for patients who choose dilation and evacuation because of fetal brain abnormalities.     

Fetal magnetic resonance imaging

PURPOSE OF REVIEW: Fetal magnetic resonance imaging is becoming more used in the evaluation of complex fetal abnormalities. Rapid advances in the technology and application of fetal magnetic resonance imaging necessitate a review of this subject. RECENT FINDINGS: Diffusion-weighted imaging, magnetic resonance spectroscopy and functional magnetic resonance imaging may allow assessment of fetal brain even before anatomical abnormalities are demonstrated. We discuss the uses of fetal magnetic resonance imaging in better assessment of pulmonary hypoplasia, congenital diaphragmatic hernia and renal anomalies. SUMMARY: The additional information from fetal magnetic resonance imaging, beyond that obtained by ultrasound, is invaluable in prenatal counseling, delivery planning and planning for pre- or postnatal intervention. As intrauterine and neonatal surgery evolve, so will the utilization of fetal magnetic resonance imaging.     

Diagnosing fetal urinary tract abnormalities: benefits of MRI compared to ultrasonography

BACKGROUND: To compare antepartum ultrasonography with magnetic resonance imaging for prenatal diagnosis of malformations in the fetal urinary tract in high risk patients during the last trimester. MATERIALS AND METHODS: The study involved 22 women and 24 fetuses with either severe oligohydramnios or ultrasonographically or clinically suspected abnormality of urinary tract. Ultrasound examination was carried out with 5 MHz abdominal convex probe and magnetic resonance imaging with superconductive 1.5 T equipment. Postnatal findings were used as reference. RESULTS: Correct diagnosis of urinary tract anomaly was done in 15 fetuses on ultrasound and in 20 fetuses on magnetic resonance imaging. Both methods enabled correct diagnosis in 12, only ultrasound in three and only magnetic resonance imaging in eight fetuses. Both methods imaged equivocally in one case. The additional information by magnetic resonance imaging was gained from five fetuses out of 12 pregnancies with oligohydramnios and from three fetuses out of ten pregnancies with normal amount of amniotic fluid. CONCLUSIONS: MRI is a valuable additional method to ultrasonography of fetal urinary tract if resolution of ultrasound is impaired for reason of oligohydramnios or technical deterioration.     

Antenatal ultrasound diagnosis of fetal malformations: possibilities, limitations and dilemmas

The antenatal ultrasound diagnosis of fetal abnormalities in 150 fetuses over the period 1975-early 1983 is reported. The perinatal outcome of the whole series has been assessed. The most frequently encountered malformations involved the central nervous system (34.9%), the nephro-urological system (17.2%), and the gastro-intestinal tract, abdominal wall and diaphragm (17.1%). Neonatal findings in incompletely explained polyhydramnions, fetal hydrops, and severe intrauterine growth retardation are also commented upon. Numerical chromosomal abnormalities were present in at least 13.3% of the malformed fetuses. The accuracy of the antenatal ultrasound diagnosis in a defined subgroup with congenital malformations resulting in perinatal death was analysed: in 76.9% one (or more) malformations were correctly diagnosed or relevant information was obtained. Comment is made on the obstetrical management and its inherent dilemmas, with appropriate references to the literature. Antenatal ultrasound, together with complementary techniques, can reach an acceptable level of accuracy, but associated anomalies may be missed. Groups for which there are different prognoses can be assessed, and serve as a guideline in perinatal management. Ethical attitudes, psychological aspects, and the possible promises of fetal treatment are briefly discussed.     

Postnatal management and outcome of prenatally diagnosed lung lesions

Advancements in fetal diagnostic imaging have increased prenatal diagnosis of many fetal anomalies. The purpose of this chapter is to review the etiology and natural history of prenatally diagnosed cystic lung lesions, including congenital cystic adenomatoid malformations (CCAM), pulmonary sequestrations (PSs), hybrid lesions, and bronchogenic cysts, and then discuss current concepts in the management and outcome of these lesions.     

Diagnosis and management of unilateral third-trimester hydrocephalus: a multidisciplinary approach

Hydrocephalus is a pathological increase in cerebrospinal fluid. This condition may occur when production exceeds absorption. Prior reports describe prenatally diagnosed unilateral hydrocephalus with varying outcomes depending on underlying brain abnormalities, karyotypic abnormalities, and infection. Prenatal ultrasound is a valuable diagnostic tool in the identification of hydrocephalus. Obstacles such as near-field artifact, additional intracranial abnormalities, fetal positioning, and maternal habitus often make the diagnosis difficult. Antenatal diagnosis is important for emotional preparation and for transfer to a tertiary center where appropriate facilities and subspecialists are available. We present a case of right-sided hydrocephalus and mild left-sided ventriculomegaly diagnosed in the third trimester. Fetal brain magnetic resonance imaging confirmed the sonographic diagnosis, which allowed the multidisciplinary fetal team to meet with the patient and formulate a management plan prior to delivery.     

Ultrafast magnetic resonance imaging of central nervous system abnormalities in utero in the second and third trimester of pregnancy: comparison with ultrasound

Objective To assess the ability of ultrafast magnetic resonance imaging to visualise abnormalities in the central nervous system of third trimester fetuses in utero and to compare the results with the current 'reference standard' of ultrasound and postnatal imaging or post-mortem data.
Design A prospective, observational study comparing the diagnostic accuracy of two imaging methods: antenatal ultrasound and antenatal magnetic resonance with each other and postnatal or post mortem data.
Population Twenty-one pregnant women of 19–36 weeks of gestation whose fetus were thought to have a central nervous system abnormality on the basis of antenatal ultrasound. The women had either not been offered or had refused a termination and were willing to have a magnetic resonance scan.
Methods A 1.5T magnetic resonance scanner used a single shot fast spin echo sequence, in three image planes. The results were compared with the ultrasound results obtained by an experienced investigator independently. A series of 21 patients, with a range of pathologies of central nervous system, were imaged. Postnatal ultrasound and/or magnetic resonance imaging, or post-mortem data were used for additional confirmation of the pathology in all cases.
Results The magnetic resonance report was different to the ultrasound in 10/21 (47.6%), magnetic resonance provided information additional to the ultrasound in 5/21 (23.8%), ultrasound and magnetic resonance results agreed in 6/21 cases (28.6%).
Conclusion Magnetic resonance in the third trimester provides a useful adjuvant to ultrasound imaging of the fetus when assessing abnormalities of the central nervous system after 19 weeks of gestation particularly if the abnormality involves the posterior fossa.     

Magnetic resonance imaging and ultrasound in the assessment of the fetal central nervous system

Ultrasound is the screening modality of choice for evaluation of the fetal central nervous system (CNS). However, in cases of difficult diagnosis further fetal investigation is desirable. Due to ultrafast magnetic resonance imaging (MRI) techniques artifacts from fetal motions are minimized. MRI involves no exposure to radiation and hence appears to be safe. Due to the better soft tissue contrast, additional investigation by MRI may extend the sonographic diagnosis of fetal CNS-anomalies. Ultrasound and MRI are complementary imaging methods in the evaluation of the fetal CNS. The most important indications for ultrasound are screening for CNS anomalies and serial assessment of the dynamic of the disorder. The most important indications for fetal MRI are the "second opinion" and investigation by fetal MRI instead of postpartum MRI (especially in cases of planned postpartum intervention). In this article the indications and limitations of ultrasound and magnetic resonance imaging in the evaluation of the fetal CNS are discussed.     

Fetal magnetic resonance imaging and three-dimensional ultrasound in clinical practice: General aspects

Ultrasonography is used routinely during pregnancy to screen and diagnose fetal anomalies. Two-dimensional ultrasound is usually adequate in women at low risk for malformations. When technical factors limit optimal evaluation or a malformation is suspected, further imaging with three-dimensional ultrasound and magnetic resonance imaging is becoming increasingly common. Three-dimensional ultrasound allows the manipulation of data acquired from two-dimensional ultrasound to recreate an infinite number of views, thereby enhancing the ability to evaluate the fetal anatomy. When three-dimensional ultrasound is either unavailable or inadequate, fetal magnetic resonance imaging permits detailed evaluation of the suspected anomaly and assesses the presence of associated anomalies. In this chapter, we review the techniques, advantages, limitations, and clinical applications of these two fetal imaging modalities.