Fetal abdominal magnetic resonance imaging

MRI in Pregnancy and Precision Medicine: A Review from Literature

Magnetic resonance imaging (MRI) offers excellent spatial and contrast resolution for evaluating a wide variety of pathologies, without exposing patients to ionizing radiations. Additionally, MRI offers reproducible diagnostic imaging results that are not operator-dependent, a major advantage over ultrasound. MRI is commonly used in pregnant women to evaluate, most frequently, acute abdominal and pelvic pain or placental abnormalities, as well as neurological or fetal abnormalities, infections, or neoplasms. However, to date, our knowledge about MRI safety during pregnancy, especially about the administration of gadolinium-based contrast agents, which are able to cross the placental barrier, is still limited, raising concerns about possible negative effects on both the mother and the health of the fetus. Contrast agents that are unable to cross the placenta in a way that is safe for the fetus are desirable. In recent years, some preclinical studies, carried out in rodent models, have evaluated the role of long circulating liposomal nanoparticle-based blood-pool gadolinium contrast agents that do not penetrate the placental barrier due to their size and therefore do not expose the fetus to the contrast agent during pregnancy, preserving it from any hypothetical risks. Hence, we performed a literature review focusing on contrast and non-contrast MRI use during pregnancy.

Descending-sigmoid colon flexure - An important but surprisingly ignored landmark

BACKGROUND

In invasive examinations of the colon, e.g. colonoscopy, the tortuosity of the colon is a crucial factor for successful completion of the procedure. If adjacent segments of the colon bend at acute angles (under 90°), endoscopy may become difficult and troublesome.

METHODS

We retrospectively enroled 227 individuals (96 female, 131 male) who underwent abdominopelvic computed tomography examination. For inclusion, subjects were required to have a negative history for colonic disease and abdominopelvic surgery. We measured the angle between the descending colon and the proximal part of the sigmoid (in degrees). In addition, the position of the descending-sigmoid flexure was assessed in relation to the left anterior superior iliac spine, the median plane, and anterior aspect of the 5th lumbar vertebra (in mm). The study protocol was reviewed and approved by the local ethics committee.

RESULTS

We visualised the descending-sigmoid flexure in all 227 subjects. In one third of cases, the flexure formed an angle smaller than/or 90°. In females, this landmark (mean ± standard deviation) was located 30.2 ± 8.4 mm from the left anterior superior iliac spine, 88.6 ± 14.2 mm from the median plane, and 115.4 ± 21.4 mm from the anterior aspect of the 5th lumbar vertebra. In males, the dimensions were: 32.1 ± 12.8 mm, 97.6 ± 15.8 mm, and 123.9 ± 22.9 mm, respectively. This landmark distance remained constant from the left anterior superior iliac spine regardless of subject age, height and weight. The other measured distances were related to age, height, weight or BMI.

CONCLUSIONS

The descending-sigmoid flexure is an important landmark in large intestine morphology situated approximately width of two fingers (3 cm) from the left anterior superior iliac spine and one hand width (9-10 cm) from the median plane. In approximately one third of the subjects, the flexure formed an angle of less than/or 90°, which can cause a problem during colonoscopy.

Utility of Magnetic Resonance Imaging in Diagnosis of Prenatal Non-Visualization of the Fetal Gallbladder: A Case-Series Study

BACKGROUND This study aimed to assess the utility of magnetic resonance imaging (MRI) in the diagnosis of prenatal non-visualization of the fetal gallbladder (PNVGB). MATERIAL AND METHODS The clinical data of 32 pregnant women with PNVGB who underwent MRI examination during the second and third trimester of pregnancy were collected and their outcomes were analyzed. RESULTS MRI showed that 26 patients (81.3%) had isolated PNVGB and 6 (18.8%) had additional malformations. In 26 patients with isolated PNVGB, 7 were found in the gallbladder on MRI and 4 were found on subsequent ultrasonography. One patient had termination of pregnancy (TOP) and 1 patient was lost to follow-up; the remaining 24 patients were known to deliver a healthy child. Among the 6 patients with additional malformations, 3 terminated their pregnancies due to combined severe abnormalities: 1 patient with horseshoe kidney and 1 with fetal echogenic bowel both had a healthy child, while 1 with fetal growth restriction (FGR) delivered a child who walked on tiptoe. CONCLUSIONS MRI contributes to identifying PNVGB detected or suspected by ultrasonography.

Magnetic resonance imaging of the fetal gastrointestinal system

In this paper the authors review the normal imaging appearance of the fetal gastrointestinal tract and patterns of fetal gastrointestinal tract obstruction. The authors include a detailed summary from esophagus to the rectum, including the expected pattern of meconium and small-bowel contents at different gestational ages. Common fetal gastrointestinal tract obstructions are reviewed with accompanying case examples, emphasizing the role of the meconium and bowel-caliber patterns in establishing differential diagnoses. This review also includes imaging pitfalls, complications of gastrointestinal tract obstruction, and implications for patient care.

How to read a fetal magnetic resonance image 101

Accurate antenatal diagnosis is essential for planning appropriate pregnancy management and improving perinatal outcomes. The provision of information vital for prognostication is a crucial component of prenatal imaging, and this can be enhanced by the use of fetal MRI. Image acquisition, interpretation and reporting of a fetal MR study can be daunting to the individual who has encountered few or none of these examinations. This article provides the radiology trainee with a general approach to interpreting a fetal MRI. The authors review the added value of prenatal MRI in the overall assessment of fetal wellbeing, discuss MRI protocols and techniques, and review the normal appearance of maternal and fetal anatomy. The paper concludes with a sample template for structured reporting, to serve as a checklist and guideline for reporting radiologists.

Normal size of the fetal adrenal gland on prenatal magnetic resonance imaging

BACKGROUND

The adrenal gland plays a vital role in fetal growth. Many disease states such as congenital adrenal hyperplasia, hemorrhage and tumors can lead to morphological changes in the gland. Ultrasound measurements of normal adrenal sizes in the fetus reported in the literature have shown a trend of increasing size with gestational age. There is no literature available on standard fetal adrenal sizes or detailed appearance by fetal MRI.

OBJECTIVE

The purpose of this study was to provide MR data on the size and signal characteristics of the fetal adrenal gland throughout the second and third trimesters.

MATERIALS AND METHODS

In this retrospective review, we selected 185 prenatal MRIs obtained from Jan. 1, 2014, to May 31, 2017, with normal abdominal findings for inclusion. The adrenal glands were identified in coronal, sagittal or axial T2-W planes and coronal T1-W plane when available. We measured the length and thickness of the medial and lateral limbs of the right and left adrenal glands and recorded signal intensity on T1-W and T2-W sequences, gender and gestational age in each case.

RESULTS

The gestational age (GA) ranged 18-37 weeks. Visibility of the adrenal glands on T2-W images was high (90.3-97.2%) up to 30 weeks of GA but declined afterward (47.5-62.2% at 31-37 weeks). Visibility on T1-W images increased with GA, ranging from 21.4% visibility at 18-22 weeks and increasing to 40% at 35-37 weeks. Mean lengths of the adrenal gland limbs steadily increased from 8.2 mm at 18-22 weeks to 11.0 mm at 35-37 weeks. In the second trimester, adrenal glands were low in signal intensity on T2-W images and were surrounded by hyperintense perirenal fatty tissue. In the third trimester, the glands became less distinct, with increasing signal and obliteration of perirenal tissue. The glands were moderately hyperintense on T1-W images throughout pregnancy, with increasing visibility as pregnancy progressed.

CONCLUSION

Normal sizes and signal intensities for adrenal glands are reported. Visibility of adrenal glands on T2-W images was 90.3-97.2% up to 30 weeks but declined thereafter. Visibility on T1-W images increased in the third trimester. Adrenal gland sizes increased with gestational age.

Fetal Physiologically Based Pharmacokinetic Models: Systems Information on the Growth and Composition of Fetal Organs

BACKGROUND

The growth of fetal organs is a dynamic process involving considerable changes in the anatomical and physiological parameters that can alter fetal exposure to xenobiotics in utero. Physiologically based pharmacokinetic models can be used to predict the fetal exposure as time-varying parameters can easily be incorporated.

OBJECTIVE

The objective of this study was to collate, analyse and integrate the available time-varying parameters needed for the physiologically based pharmacokinetic modelling of xenobiotic kinetics in a fetal population.

METHODS

We performed a comprehensive literature search on the physiological development of fetal organs. Data were carefully assessed, integrated and a meta-analysis was performed to establish growth trends with fetal age and weight. Algorithms and models were generated to describe the growth of these parameter values as functions of age and/or weight.

RESULTS

Fetal physiologically based pharmacokinetic parameters, including the size of the heart, liver, brain, kidneys, lungs, spleen, muscles, pancreas, skin, bones, adrenal and thyroid glands, thymus, gut and gonads were quantified as a function of fetal age and weight. Variability around the means of these parameters at different fetal ages was also reported. The growth of the investigated parameters was not consistent (with respect to direction and monotonicity).

CONCLUSION

Despite the limitations identified in the availability of some values, the data presented in this article provide a unique resource for age-dependent organ size and composition parameters needed for fetal physiologically based pharmacokinetic modelling. This will facilitate the application of physiologically based pharmacokinetic models during drug development and in the risk assessment of environmental chemicals and following maternally administered drugs or unintended exposure to environmental toxicants in this population.

Fetal MRI for dummies: what the fetal medicine specialist should know about acquisitions and sequences

Fetal MRI is an increasingly used tool in the field of prenatal diagnosis. While US remains the first line screening tool, as an adjuvant imaging tool, MRI has been proven to increase diagnostic accuracy and change patient counseling. Further, there are instances when US may not be sufficient for diagnosis. As a multidisciplinary field, it is important that every person involved in the referral, diagnosis, counseling and treatment of the patients is familiar with the basic principles, indications and findings of fetal MRI. The purpose of the current paper is to equip radiologists and non-radiologists with basic MRI principles and essential topics in patient preparation and provide illustrative examples of when fetal MRI may be used. This aims to aid the referring clinician in better selecting and improve patient counseling prior to arrival in the radiology department and, ultimately, patient care.

Use of Magnetic Resonance Imaging in Evaluating Fetal Brain and Abdomen Malformations during Pregnancy

Magnetic resonance imaging (MRI) is used as a clarifying technique after a high-resolution ultrasound examination during pregnancy. Combining ultrasound with MRI, additional diagnostic information is obtained or ultrasound diagnosis is frequently corrected. High spatial resolution provides accurate radiological imaging of internal organs and widens possibilities for detecting perinatal development disorders. The safety of MRI and the use of intravenous contrast agent gadolinium are discussed in this article. There is no currently available evidence that MRI is harmful to the fetus, although not enough research has been carried out to prove enduring safety. MRI should be performed when the benefit outweighs the potential side effects. The narrative review includes several clinical cases of fetal MRI performed in Vilnius University Hospital Santaros Clinics.

Decreased rectal meconium signal on MRI in fetuses with open spinal dysraphism

OBJECTIVE

To evaluate rectal meconium signal in fetuses with open spinal dysraphism and correlate findings with postnatal exam.

METHODS

This is a single-institution Institutional Review Board-approved Health Insurance Portability and Accountability Act (HIPAA) compliant retrospective analysis of fetal MRIs of open spinal dysraphism from 2004 to 2016. Fetuses with diagnostic T1-weighted images and postnatal follow-up at our institution were included.

RESULTS

A total of 115 fetuses (average gestational age 23.9 ± 3.6 weeks) met inclusion criteria. Of these, 80% (92/115) had T1 hyperintense rectal meconium signal. Average height of the meconium column, measured from the base of the bladder to its most inferior extent, was 9.2 ± 4.3 mm in fetuses ≥20-week gestational age and 11.1 ± 4.4 mm in fetuses ≥23-week gestational age (n = 110) . None had bowel dilation. One of 115 fetuses had a simple form of anorectal malformation allowing complete repair in the neonatal period, but this fetus had a normal meconium column height on fetal MRI of 22 mm. The remaining 23/115 fetuses with lack of normal rectal meconium signal were born without evidence of anorectal malformation.

CONCLUSION

Decreased or absent T1-hyperintense rectal meconium signal in fetuses with open spinal dysraphism does not correlate with imperforate anus postnatal and may be a reflection of neurogenic bowel in this patient population.

The development of the dorsal mesentery in human embryos and fetuses

The vertebrate intestine has a continuous dorsal mesentery between pharynx and anus that facilitates intestinal mobility. Based on width and fate the dorsal mesentery can be subdivided into that of the caudal foregut, midgut, and hindgut. The dorsal mesentery of stomach and duodenum is wide and topographically complex due to strong and asymmetric growth of the stomach. The associated formation of the lesser sac partitions the dorsal mesentery into the right-sided "caval fold" that serves as conduit for the inferior caval vein and the left-sided mesogastrium. The thin dorsal mesentery of the midgut originates between the base of the superior and inferior mesenteric arteries, and follows the transient increase in intestinal growth that results in small-intestinal looping, intestinal herniation and, subsequently, return. The following fixation of a large portion of the abdominal dorsal mesentery to the dorsal peritoneal wall by adhesion and fusion is only seen in primates and is often incomplete. Adhesion and fusion of mesothelial surfaces in the lesser pelvis results in the formation of the "mesorectum". Whether Toldt's and Denonvilliers' "fasciae of fusion" identify the location of the original mesothelial surfaces or, alternatively, represent the effects of postnatal wear and tear due to intestinal motility and intra-abdominal pressure changes, remains to be shown. "Malrotations" are characterized by growth defects of the intestinal loops with an ischemic origin and a narrow mesenteric root due to insufficient adhesion and fusion.

Fetal MRI in management of complicated meconium ileus: Prenatal and surgical imaging

OBJECTIVE

To review fetal MRI cases surgically proven to have meconium ileus (MI) and obstruction, describe the common fetal MRI findings that distinguish cases of complicated MI, and to compare these findings with surgical images and perinatal outcomes.

METHOD

We performed a retrospective review of all fetal MRI examinations and the corresponding medical record from our tertiary care children's hospital over an 18-month period. Postnatal management and outcomes were reviewed for these patients, and those patients with surgical or postmortem diagnosis of complicated MI were included in the study.

RESULTS

Our analysis revealed 7 cases. In this cohort, 3 imaging features of the fetal bowel were repeatedly seen: gradient appearance of intraluminal bowel contents, abnormally localized meconium signal, and collapsed appearance of the colon on MRI. Surgical diagnoses confirmed MI. All live-born infants underwent surgical repair.

CONCLUSION

Fetal MRI should be included in the diagnostic algorithm of any pregnancy where fetal bowel obstruction is suspected to better risk stratify patients.

Evaluation of Fetal Thyroid with 3D Gradient Echo T1-weighted MR Imaging

Purpose:

The characteristics of fetal thyroid on magnetic resonance (MR) imaging, including normal thyroid and disorders other than goiter have not been fully evaluated. Our aim was to assess fetal thyroid using three dimensional (3D) gradient echo (GRE) T₁-weighted MR imaging and to examine the usefulness of this modality.

Materials and Methods:

The study included 27 3D GRE T₁-weighted images from 26 fetuses. The largest possible region of interest (ROI) within the thyroid at the slice level depicting the thyroid was manually defined and three circular ROIs on neck muscle were manually defined on the image slices showing the highest signal intensity (SI) of the thyroid. Maximum and mean thyroid-to-muscle SI ratios (SIRs) were then calculated as SIR = maximum or mean thyroid SI/muscle SI.

Results:

The thyroid could not be identified in two cases. Fetal thyroid function was normal in 17 cases, and there were 7 cases of hypothyroidism (6 transient and 1 thyroid dysgenesis). There was no linear relationship between mean and maximum SIR and gestational age. The mean and maximum SIR in the cases of normal fetal thyroid were 1.85 ± 0.20 and 2.61 ± 0.39, and the mean and maximum SIR in fetal hypothyroidism were 1.58 ± 0.20 and 2.13 ± 0.37. Mean (P = 0.0088) and maximum (P = 0.0221) SIR values were significantly different between euthyroid and hypothyroid fetuses.

Conclusion:

Thyroid SIR measurement provided useful information regarding fetal thyroid function.

Prenatal diagnosis of bowel malposition using T2-weighted fetal MRI sequences

OBJECTIVE

The goal of this study was to investigate the capability of T2-weighted magnetic resonance imaging (MRI) in revealing fetal bowel malposition.

MATERIALS AND METHODS

All fetal MRI examinations (excluding central nervous system MRI examinations) performed in our department from January 2005 to January 2014 were retrospectively studied by 2 independent observers for situs, stomach and jejunum location on T2-weighted images. Patients data were also reviewed for results of ultrasound examinations, MRI indication, and gestational age. Abnormally positioned jejunums were classified into 3 groups: intrathoracic (A), extra-fetal (B) and abnormal intra-fetal (C). Prenatal data were compared to postnatal imaging, surgery or autopsy findings that served as standard of reference.

RESULTS

A total of 709 fetal MRI examinations were analyzed. In 64 fetus (9%), the jejunum was not present in the left subgastric area on T2-weighted MR images. In these 64 fetuses, proximal jejunum was intrathoracic (41/64, 64%, group A), extra-fetal (11/64, 17%, group B), or intra-abdominal but abnormally positioned (12/64, 19%, group C). Interobserver agreement was 100%. All diagnoses for fetuses in groups A and B (52 cases) were confirmed postnatally (41 cases) or at autopsy (11 cases). In group C, bowel malposition was suspected after ultrasound in only 2/12 fetuses (16.6%); it was confirmed postnatally in 1 fetus but not confirmed in the remaining one. In the 10 remaining fetuses (83%), malposition was confirmed postnatally although not initially suspected.

CONCLUSION

T2-weighted fetal MR images are useful for the prenatal diagnosis of bowel malposition, even when they are unsuspected on ultrasound examination.

Imaging Evaluation of Fetal Megacystis: How Can Magnetic Resonance Imaging Help?

Evaluation of the kidneys, bladder, and amniotic fluid volume forms part of any standard obstetrical ultrasound. When a fetal genitourinary anomaly is suspected, a more detailed evaluation is necessary. This detailed imaging can be challenging in the setting of decreased or absent amniotic fluid or large maternal body habitus, and in complex malformations. In these situations, magnetic resonance imaging can help to better define the fetal anatomy and provide a more confident and specific prenatal diagnosis.

When Closure Fails: What the Radiologist Needs to Know About the Embryology, Anatomy, and Prenatal Imaging of Ventral Body Wall Defects

Ventral body wall defects (VBWDs) are one of the main categories of human congenital malformations, representing a wide and heterogeneous group of defects sharing a common feature, that is, herniation of one or more viscera through a defect in the anterior body wall. Gastroschisis and omphalocele are the 2 most common congenital VBWDs. Other uncommon anomalies include ectopia cordis and pentalogy of Cantrell, limb-body wall complex, and bladder and cloacal exstrophy. Although VBWDs are associated with multiple abnormalities with distinct embryological origins and that may affect virtually any system organs, at least in relation to anterior body wall defects, they are thought (except for omphalocele) to share a common embryologic mechanism, that is, a failure involving the lateral body wall folds responsible for closing the thoracic, abdominal, and pelvic portions of the ventral body wall during the fourth week of development. Additionally, many of the principles of diagnosis and management are similar for these conditions. Fetal ultrasound (US) in prenatal care allows the diagnosis of most of such defects with subsequent opportunities for parental counseling and optimal perinatal management. Fetal magnetic resonance imaging may be an adjunct to US, providing global and detailed anatomical information, assessing the extent of defects, and also helping to confirm the diagnosis in equivocal cases. Prenatal imaging features of VBWDs may be complex and challenging, often requiring from the radiologist a high level of suspicion and familiarity with the imaging patterns. Because an appropriate management is dependent on an accurate diagnosis and assessment of defects, radiologists should be able to recognize and distinguish between the different VBWDs and their associated anomalies. In this article, we review the relevant embryology of VBWDs to facilitate understanding of the pathologic anatomy and diagnostic imaging approach. Features will be illustrated with prenatal US and magnetic resonance imaging and correlated with postnatal and clinical imaging.

Fetal MRI: A Technical Update with Educational Aspirations

Fetal magnetic resonance imaging (MRI) examinations have become well-established procedures at many institutions and can serve as useful adjuncts to ultrasound (US) exams when diagnostic doubts remain after US. Due to fetal motion, however, fetal MRI exams are challenging and require the MR scanner to be used in a somewhat different mode than that employed for more routine clinical studies. Herein we review the techniques most commonly used, and those that are available, for fetal MRI with an emphasis on the physics of the techniques and how to deploy them to improve success rates for fetal MRI exams. By far the most common technique employed is single-shot T2-weighted imaging due to its excellent tissue contrast and relative immunity to fetal motion. Despite the significant challenges involved, however, many of the other techniques commonly employed in conventional neuro- and body MRI such as T1 and T2*-weighted imaging, diffusion and perfusion weighted imaging, as well as spectroscopic methods remain of interest for fetal MR applications. An effort to understand the strengths and limitations of these basic methods within the context of fetal MRI is made in order to optimize their use and facilitate implementation of technical improvements for the further development of fetal MR imaging, both in acquisition and post-processing strategies.

Fetal adrenal gland in the second half of gestation: morphometrical assessment with 3.0T post-mortem MRI

Background

The morphometry of fetal adrenal gland is rarely described with MRI of high magnetic field. The purpose of this study is to assess the normal fetal adrenal gland length (AL), width (AW), height (AH), surface area (AS) and volume (AV) in the second half of gestation with 3.0T post-mortem MRI.

Methods and Findings

Fifty-two fetal specimens of 23–40 weeks gestational age (GA) were scanned by 3.0T MRI. Morphological changes and quantitative measurements of the fetal adrenal gland were analyzed. Asymmetry and sexual dimorphism were also obtained. The shape of the fetal adrenal gland did not change substantially from 23 to 40 weeks GA. The bilateral adrenal glands appeared as a ‘Y’, pyramidal or half-moon shape after reconstruction. There was a highly linear correlation between AL, AW, AH, AS, AV and GA. AW, AH, AS and AV were larger for the left adrenal gland than the right. No sexual dimorphism was found.

Conclusions

Our data delineated the normal fetal adrenal gland during the second half of gestation, and can serve as a useful precise reference for anatomy or in vivo fetus.

Fetal MRI: An approach to practice: A review

MRI has been increasingly used for detailed visualization of the fetus in utero as well as pregnancy structures. Yet, the familiarity of radiologists and clinicians with fetal MRI is still limited. This article provides a practical approach to fetal MR imaging. Fetal MRI is an interactive scanning of the moving fetus owed to the use of fast sequences. Single-shot fast spin-echo (SSFSE) T2-weighted imaging is a standard sequence. T1-weighted sequences are primarily used to demonstrate fat, calcification and hemorrhage. Balanced steady-state free-precession (SSFP), are beneficial in demonstrating fetal structures as the heart and vessels. Diffusion weighted imaging (DWI), MR spectroscopy (MRS), and diffusion tensor imaging (DTI) have potential applications in fetal imaging. Knowing the developing fetal MR anatomy is essential to detect abnormalities. MR evaluation of the developing fetal brain should include recognition of the multilayered-appearance of the cerebral parenchyma, knowledge of the timing of sulci appearance, myelination and changes in ventricular size. With advanced gestation, fetal organs as lungs and kidneys show significant changes in volume and T2-signal. Through a systematic approach, the normal anatomy of the developing fetus is shown to contrast with a wide spectrum of fetal disorders. The abnormalities displayed are graded in severity from simple common lesions to more complex rare cases. Complete fetal MRI is fulfilled by careful evaluation of the placenta, umbilical cord and amniotic cavity. Accurate interpretation of fetal MRI can provide valuable information that helps prenatal counseling, facilitate management decisions, guide therapy, and support research studies.

Fetal MRI of cloacal exstrophy

BACKGROUND

Prenatal ultrasonographic (US) diagnosis of cloacal exstrophy (CE) is challenging.

OBJECTIVE

To define the fetal MRI findings in CE.

MATERIALS AND METHODS

We performed a retrospective review of eight patients with CE. Imaging was performed between 22 weeks and 36 weeks of gestation with US in four and MRI in eight fetuses. Abdominal wall, gastrointestinal/genitourinary, and spine and limb abnormalities detected were compared with postnatal evaluation.

RESULTS

US failed to display CE in one of the four fetuses. Fetal MRI confirmed CE in all eight fetuses by demonstrating absence of a normal bladder and lack of meconium-filled rectum/colon, associated with protuberant pelvic contour and omphalocele. These findings correlated postnatally with CE, atretic hindgut and omphalocele. One fetus had imaging before rupture of the cloacal membrane, showing a protruding pelvic cyst. Absent bladder was noted in the remaining seven fetuses. Confirmed skin-covered spinal defects were noted in seven fetuses, low conus/tethered cord in one and clubfoot in three. Six fetuses had renal anomalies, two had hydrocolpos and one had ambiguous genitalia.

CONCLUSION

Fetal MRI provides a confident diagnosis of CE when a normal bladder is not identified, there is a protuberant abdominopelvic contour and there is absence of meconium-filled rectum and colon. Genitourinary and spinal malformations are common associations.

A morphometric study of suprarenal gland development in the fetal period

PURPOSE

The present study's purpose was to examine the morphometric development of the suprarenal gland using anatomic dissection methods during the fetal period.

METHODS

This study was performed on 172 human fetuses (76 males and 96 females) and 344 fetal suprarenal glands obtained from ages 9-40 weeks of gestation with no external pathology or anomaly. Fetuses were divided into 4 groups between gestational ages as follows: Group 1, 9-12 weeks (first trimester); Group 2, 13-25 weeks (second trimester); Group 3, 26-37 weeks (third trimester); and Group 4, 38-40 weeks (full term). Also, the fetuses were grouped into monthly cohorts: 9-12 weeks 3rd month, 13-16 weeks 4th month, 17-20 weeks 5th month, 21-24 weeks 6th month, 25-28 weeks 7th month, 29-32 weeks 8th month, 33-36 weeks 9th month, and 37-40 weeks 10th month. The suprarenal glands were dissected in the abdominal cavity. The dimensions (width, length, and thickness), volumes and weights of the suprarenal glands were evaluated. The ratio of the fetal suprarenal gland weight/fetal body weight, the ratio of the fetal suprarenal gland volume/fetal kidney volume, and the ratio of the fetal suprarenal gland dimensions/fetal kidney dimensions were evaluated.

RESULTS

Mean values and standard deviations of all parameters according to gestational weeks and trimesters were calculated. It is found that all parameters increase with gestational age. There was significant correlation between gestational age and all parameters (p < 0.001). No significant differences were observed between sexes for any of the parameters (p > 0.05). There was no difference between the right and left sides of parameters except the thickness of the suprarenal glands. The left suprarenal glands were thicker than the right. The ratio of suprarenal volumes to kidney volumes was determined, and we observed that the ratio decreased during the fetal period.

CONCLUSIONS

We believe that the results obtained from this study will be beneficial in understanding the development of suprarenal glands and also contribute to future studies in obstetrics, perinatology, and fetopathology.

Fetal bowel anomalies--US and MR assessment

The technical quality of prenatal US and fetal MRI has significantly improved during the last decade and allows an accurate diagnosis of bowel pathology prenatally. Accurate diagnosis of bowel pathology in utero is important for parental counseling and postnatal management. It is essential to recognize the US presentation of bowel pathology in the fetus in order to refer the patient for further evaluation or follow-up. Fetal MRI has been shown to offer some advantages over US for specific bowel abnormalities. In this paper, we review the normal appearance of the fetal bowel on US and MRI as well as the typical presentations of bowel pathologies. We discuss more specifically the importance of recognizing on fetal MRI the abnormalities of size and T1-weighted signal of the meconium-filled distal bowel.

Current advances in prenatal imaging of congenital diaphragmatic [corrected] hernia

Congenital diaphragmatic hernia, despite advances in therapy, remains a complex condition with significant morbidity and mortality. The etiology of the disorder is still incompletely understood, though the pulmonary hypoplasia and pulmonary hypertension that develop secondarily must be overcome to improve survival. Prenatal US and fetal MRI have helped in the development of a greater understanding of this disease. Also with these modalities, measurement techniques have been developed in an attempt to provide prognosticators for the development of pulmonary hypoplasia and pulmonary hypertension. There is a broad range of approaches for performing these measurements, and variability among imaging centers is noted. Despite inconsistent approaches, these techniques have become the foundation for counseling and prenatal and postnatal therapy. It is hoped that with further research with prenatal US and fetal MRI and the development of innovative medical and surgical therapies that the morbidity and mortality of children with congenital diaphragmatic hernias can be significantly reduced.

Male sexual development in utero: testicular descent on prenatal magnetic resonance imaging

OBJECTIVE

To visualize in utero male fetal testicular descent on magnetic resonance imaging (MRI) and to correlate it with gestational age.

METHODS

This retrospective study included 202 MRI examination results of 199 male fetuses (17-39 gestational weeks) with normal anatomy or minor congenital abnormalities, following suspicion of anomalies on prenatal ultrasound examination. Using a 1.5-Tesla unit, multiplanar T2-weighted sequences were applied using a standard protocol to image and identify the scrotal content. The relative frequencies of unilateral and bilateral testicular descent were calculated and correlated with gestational age.

RESULTS

Between 17 and 25 gestational weeks, neither unilateral nor bilateral testicular descent was visualized on MRI. Testicular descent was first observed at 25 + 4 weeks, in 7.7% of cases. 12.5% of 27-week fetuses showed unilateral descent and 50% showed bilateral descent. Bilateral descent was observed in 95.7% of cases, on average, from 30 to 39 weeks.

CONCLUSIONS

Our results chart the time course of testicular descent on prenatal MRI, which may be helpful in the identification of normal male sexual development and in the diagnosis of congenital abnormalities, including the early detection of cryptorchidism.

Fetal gastrointestinal MRI: all that glitters in T1 is not necessarily colon

BACKGROUND

It has been described that both the colon and distal ileum present with a physiological hypersignal on T1-weighted sequences during the second and third trimesters of pregnancy because of their protein-rich meconium content, it was unclear whether the normal characteristics that have been described on fetal MRI can be applied to gastrointestinal (GI) obstructions.

OBJECTIVE

To analyse the localisation value of T1 hypersignal within dilated bowel loops in fetuses with gastrointestinal tract obstruction.

MATERIALS AND METHODS

A retrospective 4-year multicentre study analysing cases of fetal GI obstruction in which MRI demonstrated T1 hypersignal content in the dilated loops. Data collected included gestational age (GA) at diagnosis, bowel appearance on US, CFTR gene mutations and amniotic levels of gastrointestinal enzymes. The suggested prenatal diagnosis was eventually compared to postnatal imaging and surgery.

RESULTS

Eleven patients were included. The median GA at US diagnosis was 23 weeks (range 13-32). In eight cases there was a single dilated loop, while several segments were affected in three. The median GA at MRI was 29 weeks (range 23-35). One case presented with cystic fibrosis mutations. Final prenatally suspected diagnoses were distal ileal atresia or colon in nine cases and proximal atresia in two. Postnatal findings were proximal jejunal atresia in nine cases and meconium ileus in two. In five cases the surgical findings demonstrated short bowel syndrome.

CONCLUSION

In cases of fetal occlusion, T1 hypersignal should not be considered as a sign of distal ileal or colonic occlusion. The obstruction may be proximal, implying a risk of small bowel syndrome, which requires adequate parental counselling.

Magnetic resonance imaging in the prenatal diagnosis of congenital diarrhea

OBJECTIVE

Congenital diarrhea is very rare, and postnatal diagnosis is often made once the condition has caused potentially lethal fluid loss and electrolyte disorders. Prenatal detection is important to improve the immediate neonatal prognosis. We aimed to describe the prenatal ultrasound and magnetic resonance (MRI) imaging findings in fetuses with congenital diarrhea.

METHODS

The study reports the pre- and postnatal findings in four fetuses that presented with generalized bowel dilatation and polyhydramnios. We analyzed the fetal ultrasound and MRI examinations jointly, then compared our provisional diagnosis with the amniotic fluid biochemistry and subsequently with the neonatal stool characteristics.

RESULTS

In each of the four cases an ultrasound examination between 22 and 30 weeks' gestation showed moderate generalized bowel dilatation and polyhydramnios suggesting intestinal obstruction. MRI examinations performed between 24 and 32 weeks' gestation confirmed that the dilatation was of gastrointestinal (GI) origin, with a signal indicating intraluminal water visible throughout the small bowel and colon. The expected hypersignal on T1-weighted sequences characteristic of physiological meconium was absent in the colon and rectum. This suggested that the meconium had been completely diluted and flushed out by the water content of the bowel. The constellation of MRI findings enabled a prenatal diagnosis of congenital diarrhea. The perinatal lab test findings revealed two cases of chloride diarrhea and two of sodium diarrhea.

CONCLUSION

Congenital diarrhea may be misdiagnosed as intestinal obstruction on prenatal ultrasound but has characteristic findings on prenatal MRI enabling accurate diagnosis; this is important for optimal neonatal management.

Three-dimensional MRI volumetric measurements of the normal fetal colon

OBJECTIVE

The use of fetal MRI markedly improves characterization of abdominal congenital anomalies. Accurate prenatal diagnosis of the level and cause of congenital intestinal obstruction is desired for optimal parental counseling and perinatal care. Because accurate diagnosis would be aided by nomograms of colonic volume, this study was conducted to determine normal colonic volumes at different gestational ages.

MATERIALS AND METHODS

This retrospective study consisted of a review of 83 fetal MRI examinations performed on fetuses with no gastrointestinal abnormalities. MRI was performed with a 1.5-T system. Axial, sagittal, and coronal T1-weighted fast gradient-refocused echo images were acquired at TR/TE, 165/2.6; flip angle, 90 degrees; matrix size, 384 x 192; slice thickness, 5 mm; field of view, 38 cm(2). Two investigators determined the region of interest in the colon by outlining areas of high signal intensity of meconium slice by slice. They then calculated colonic luminal volume in the regions of interest. Colonic luminal volumes were reported relative to gestational age and abdominal circumference. Normative curves were generated, and interobserver and intraobserver analyses were performed.

RESULTS

Seventeen of the 83 fetuses (20%) were excluded because of movement artifacts on the images. Normal colonic luminal volume increased exponentially with gestational age and abdominal circumference. The range of colonic luminal volumes at 20-37 weeks' gestational age was 1.1-65 mL. Variation of volume was greater at advanced gestational age. Interobserver and intraobserver correlation was good.

CONCLUSION

This study yielded preliminary volumetric measurements of the normal fetal colon at 20-37 weeks of gestational age that suggest the fetal colon grows exponentially.

Prenatal ultrasound and fetal MRI: the comparative value of each modality in prenatal diagnosis

Fetal MRI is used with increasing frequency as an adjunct to ultrasound (US) in prenatal diagnosis. In this review, we discuss the relative value of both prenatal US and MRI in evaluating fetal and extra-fetal structures for a variety of clinical indications. Advantages and disadvantages of each imaging modality are addressed. In summary, MRI has advantages in demonstrating pathology of the brain, lungs, complex syndromes, and conditions associated with reduction of amniotic fluid. At present, US is the imaging method of choice during the first trimester, and in the diagnosis of cardiovascular abnormalities, as well as for screening. In some conditions, such as late gestational age, increased maternal body mass index, skeletal dysplasia, and metabolic disease, neither imaging method may provide sufficient diagnostic information.

MR imaging characteristics of the normal fetal gastrointestinal tract and abdomen

Fetal magnetic resonance imaging (MRI) is considered a valuable second line imaging tool for confirmation, completion and correction of complex fetal ultrasonography findings. Fetal MRI has proven its value in pathologies of the central nervous system. Few studies have focussed on the value of fetal MRI in abdominal pathologies. With the continuing advances in hardware and software, fetal MRI is progressively valuable in fetal abdominal pathologies. A proper knowledge of the normal fetal abdominal anatomy and signal intensities is essential. The current manuscript reviews normal fetal abdominal anatomy.

MRI with diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) assessment in the evaluation of normal and abnormal fetal kidneys: preliminary experience

OBJECTIVE

To investigate apparent diffusion coefficient (ADC) mapping with the measurement of renal tissue ADC value of normal and pathological fetal kidneys at various gestational ages (GAs).

METHODS

Fifty pregnant women underwent magnetic resonance images (MRI) after ultrasound (US) for suspected fetal genitourinary disorders (16) or for suspected disorders in other organs (34). A multiplanar study of urinary system was obtained by using conventional T2-weighted sequences and echo planar imaging (EPI); Diffusion-weighted images and ADC maps were evaluated. The renal tissue ADC value was measured for all normal and abnormal fetuses and related to GA.

RESULTS

MRI confirmed urinary anomalies in 15 fetuses [2 renal developmental variants, 2 nephropathies, 4 multicystic dysplastic kidneys (MCDK), 7 renal tract dilatations] and detected normal kidneys in the remaining 35 fetuses. Normal renal parenchyma showed bright signal on diffusion-weighted images with ADC values ranging from 1,065 to 1,327 microm(2)/s with a tendency to decrease over GA. A pathological ADC was detected in cases of bilateral MCDK, huge dilatations and in cases of nephropathies.

CONCLUSION

Diffusion-weighted imaging (DWI) with ADC mapping can be used in the evaluation of fetal renal parenchyma and may become a tool of assessing function of the fetal kidney by means of measurement of renal tissue ADC values.

Fetal magnetic resonance imaging in the antenatal diagnosis and management of hydrocolpos

Hydrocolpos should be considered systematically when an abdominopelvic cystic mass is diagnosed in a female fetus. Because the prognosis and neonatal management of isolated hydrocolpos with spontaneous resolution differs greatly from that of hydrocolpos associated with a cloacal malformation, it is important to ascertain prenatally whether there are associated anomalies. We report the prenatal characteristics of three fetuses with hydrocolpos; in two cases there was spontaneous resolution and one infant was born with digestive tract atresia. The principal ultrasound findings were an oblong anechoic pelvic mass with or without a sagittal septum, located behind a normal bladder. On magnetic resonance imaging (MRI), the cervical imprint on the vagina confirmed the diagnosis of hydrocolpos and helped to diagnose cloacal malformation by demonstrating the absence of meconium beside the bladder on T1 sequences. Our cases show that MRI is useful for differentiating isolated hydrocolpos from hydrocolpos associated with cloacal malformation.

Investigation of normal organ development with fetal MRI

The understanding of the presentation of normal organ development on fetal MRI forms the basis for recognition of pathological states. During the second and third trimesters, maturational processes include changes in size, shape and signal intensities of organs. Visualization of these developmental processes requires tailored MR protocols. Further prerequisites for recognition of normal maturational states are unequivocal intrauterine orientation with respect to left and right body halves, fetal proportions, and knowledge about the MR presentation of extrafetal/intrauterine organs. Emphasis is laid on the demonstration of normal MR appearance of organs that are frequently involved in malformation syndromes. In addition, examples of time-dependent contrast enhancement of intrauterine structures are given.

Foetal magnetic resonance imaging and echogenic bowel

OBJECTIVES

To evaluate how foetal magnetic resonance imaging (MRI) may change the diagnosis in cases of ultrasound (U/S) findings of echogenic bowel (EB).

METHODS

Seventeen foetuses with EB underwent serial U/S examinations, foetal MRI, cystic fibrosis screening and maternal viral serologic tests. MRI protocol included T2-weighted half-Fourier acquired single-shot turbo spin-echo (HASTE) sequence and gradient echo (GE) T1-weighted images. Foetal abdominal MRI analyzed patterns were size and signal of small bowel, colon and rectum, ascites and abdominal mass. All neonates had complete clinical examination, abdominal sonography, and a 6 months clinical follow-up.

RESULTS

Eleven foetuses with isolated EB had normal MRI and normal outcome. In comparison, all the 6 foetuses whose U/S patterns showed associated signs had abnormal MRI (p < 0.001). Five had proven pathology (83.3%: 5/6) and only 1 (16.7%: 1/6) had no proven pathology and normal postnatal outcome (p = 0.001). For those five, foetal MRI showed bowel abnormalities with one case of bowel duplication and four cases of bowel obstruction. Two out of the four cases of bowel obstruction were genetically diagnosed as cystic fibrosis. The two remaining cases were diagnosed as ileal atresia.

CONCLUSION

MRI could provide additive information in cases of EB associated with bowel dilatation.