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      Magnetic Resonance Imaging Diagnosis of Volvulus through Mesenteric Defect in Neonate

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          Abstract

          Antenatal midgut volvulus is a rare surgical emergency in which bowel is severely compromised. Rarely the etiology is a mesenteric defect. Early diagnosis is essential and lifesaving in the immediate newborn period. Typically upper gastrointestinal or ultrasound imaging can be suggestive of the diagnosis of volvulus in the neonate. Sometimes, however, the diagnosis may be elusive. Herein, we report on the use of neonatal magnetic resonance imaging to diagnose a midgut volvulus that occurred through a congenital mesenteric defect.

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          MRI evaluation and safety in the developing brain.

          Magnetic resonance imaging (MRI) evaluation of the developing brain has dramatically increased over the last decade. Faster acquisitions and the development of advanced MRI sequences, such as magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), perfusion imaging, functional MR imaging (fMRI), and susceptibility-weighted imaging (SWI), as well as the use of higher magnetic field strengths has made MRI an invaluable tool for detailed evaluation of the developing brain. This article will provide an overview of the use and challenges associated with 1.5-T and 3-T static magnetic fields for evaluation of the developing brain. This review will also summarize the advantages, clinical challenges, and safety concerns specifically related to MRI in the fetus and newborn, including the implications of increased magnetic field strength, logistics related to transporting and monitoring of neonates during scanning, and sedation considerations, and a discussion of current technologies such as MRI conditional neonatal incubators and dedicated small-foot print neonatal intensive care unit (NICU) scanners.
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            Fetal MRI: An approach to practice: A review

            Introduction Although ultrasound (US) remains the predominant modality for evaluating disorders related to pregnancy, fetal MRI has been increasingly used. In contradistinction to US, MRI visualization of the fetus is not significantly limited by maternal obesity, fetal position, or oligohydramnios and visualization of the brain is not restricted by the ossified skull [1,2]. Through its superior soft tissue contrast resolution, MRI is able to distinguish individual fetal structures such as lung, liver, kidney, and bowel [3]. Moreover, MRI provides multiplanar imaging as well a large field of view, facilitating examination of fetuses with large or complex anomalies, and visualization of the lesion within the context of the entire fetal body [4]. However, fetal MRI study may give limited diagnostic information in early gestational age due to the small size of the fetus and fetal movement [5]. The purpose of this article is to provide a practical approach for radiologists and clinicians to fetal MRI performance and interpretation by adhering to guidelines. Fetal MRI technique, including recent advances, is discussed. The normal developing anatomy of the fetus and pregnancy structures is described to contrast with wide spectrum of abnormalities. Fetal MR appearance is demonstrated using different sequences. The current and future anticipated role of fetal MRI in supporting prenatal counseling, fetal therapy, and research studies are highlighted. Fetal MRI ethics MRI is a noninvasive diagnostic examination that does not involve ionizing radiation with no known associated negative side effects or reported delayed sequels [6]. The American College of Radiology white paper on MR safety states that pregnant patients can be accepted to undergo MR images at any stage of pregnancy if the risk-benefit ratio to the patient warrants that the study be performed [7] and only if other non-ionizing diagnostic imaging methods are inadequate. However, it is prudent to wait until 17–18th weeks of gestation before performing fetal MRI because of the potential risk to the developing fetus and the current limitations of fetal MRI created by the small size and excessive motion of younger fetuses [8]. A written informed consent is usually required from the pregnant woman prior to fetal MRI. Indications for fetal MRI: an overview Indications for fetal MRI include the confirmation of inconclusive sonographic findings and the evaluation of sonographically-occult diagnoses. It is unlikely that MRI will supplant US in the primary evaluation of pregnancy status and fetal well-being [1,2,5,8]. The primary indications of fetal MRI according to the recommendations of the American College of Radiology (ACR), and Society for Pediatric Radiology (SPR) [5] are included in Table 1. MRI is usually required only for a certain anatomic region, whereas a complete anatomic survey of the fetus is not required. The most common indications for fetal MRI are neurological. MRI is commonly used to investigate underlying etiologies of ventriculomegaly and morphologic brain abnormalities that are not as readily depicted with US such as dysgenesis of corpus callosum, malformations of cortical development, and posterior fossa anomalies [5,8]. Fetal MRI may detect subtle neural tube defects not shown by US and determine the level of the defect in myelomeningocele for potential fetal surgery [2,5,8,9]. The next common indication for fetal MRI is evaluation of suspicious thoracic masses. MRI has the advantage over US in differentiating the liver and bowel loops from lung tissue or masses; this aids in differentiating a congenital diaphragmatic hernia from a pulmonary mass [3]. Other indications include suspected airway obstruction caused by neck or thoracic masses. While airway can be difficult to evaluate fully with US because of artifact related to adjacent bony structures and fetal position, the fluid-filled fetal airways are well seen on T2-weighted MR images [1,3]. MRI could be helpful in providing tissue characterization of fetal abdominal masses when US study is nonspecific [1]. Because of the characteristic signal intensity of meconium, fetal MRI can distinguish marked bowel dilatation from cystic masses such as choledochal cyst and ovarian cyst [3]. MRI depicts well fetal masses in the context of whole body of the fetus in multiple planes, which may be underestimated by US because of obscuration by bony structures or fetal position [3,4]. MRI is particularly useful in the assessment of pregnancies complicated by oligohydramnios which can limit the diagnostic sensitivity of US [1,3]. Fetal MRI technique Sequences Development of fast MRI sequences significantly decreased fetal motion artifacts and eliminated the need for fetal sedation. A variety of fast MRI sequences are used to obtain T1- and T2-weighted images. The names and the acronyms for these sequences vary across the MR manufacturers (see Table 2). The most widely used sequence in fetal imaging is however, the single-shot fast spin-echo (SSFSE). Since SSFSE is based on single slice acquisition, fetal motion typically affects the particular slice that is being acquired while motion occurs [10]. T1-weighted images are typically acquired using two-dimensional gradient echo (2D GRE) sequences as well as a faster version of the GRE sequence called ultrafast gradient echo sequences or turbo fast low-angle shot (FLASH). Contrary to SSFSE acquisition schemes, in the gradient echo sequences all slices are acquired simultaneously. Subsequently, in the event of slight fetal movement anytime during the acquisition period, all slices are degraded by motion artifacts. In addition, spatial resolution is lower compared to SSFSE (Fig. 1) [2]. T1-weighted sequences provide little information over the T2-weighted SSFSE sequences; however, T1 weighted images are the sequence of choice for detection of hemorrhage, calcification, fat deposition and the fetal organs with high T1-hyperintensity such as thyroid and liver [8,10]. T1-weighted fat suppression images can increase the dynamic range of fetal MRI and its ability to more sensitive and specific detection of hemorrhage or fat [9]. In advanced stages of gestation, T1 weighted sequences are also used for the study of bone marrow and normal bone developmental stages [10]. Fetal MRI is also performed using balanced steady-state free precession (SSFP) sequences as balanced fast field echo (b-FFE) [11,12]. In the case of fetal brain imaging both SSFSE and b-FEE sequences provide comparable image quality especially in the 2nd trimester; however, the axonal myelination in the third trimester is better delineated by the latter sequence [12]. In addition, b-FEE is a preferred sequence for visualization of the fetal heart and vessels [11]. With a three times lower RF heat deposition than SSFSE sequence, b-FFE is considered to be a safer in fetal MRI [12]. Advanced MRI techniques Advanced MRI techniques such as diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS) have been applied to fetal MRI [8,10,13,14]. Diffusion imaging of the fetal brain has the potential applications for both developmental and destructive brain processes [8]. Although diffusion-tensor imaging (DTI) has been applied to fetal brain imaging; however, its clinical application is currently limited by its long acquisition times [14]. MRS imaging may provide prognostic information on brain function by assessing the risk of hypoxia through the detection of increased creatine (Cr) content [13]. Future sequences can take advantage of parallel imaging to decrease the scan time as well as increasing the signal to noise ratio (SNR) and image resolution [10,14]. Patient preparation and imaging protocols Fetal MRI is usually performed on a 1.5 T superconducting magnet using a phased-array torso surface coil. Even with rapid image acquisition, motion can still affect the quality of the fetal MRI. Certain clinical measures can be taken to reduce motion artifacts during the study such as having the mother take nothing by mouth for at least 4 h prior the scan to prevent postprandial motion and to make sure that she empties her bladder before the study [8]. Generally the mother lies supine during the examination. In the case the mother does not tolerate the supine position. MRI can be performed in the left lateral decubitus. An initial localizer is obtained in the three orthogonal planes with respect to the mother’s imaging planes, using 6–8-mm SSFSE T2-weighted sections with a 1–2-mm gap and a large field of view of (320–400 mm). Scout acquisition is used for the initial fetal visualization; for optimal signal intensity in the subsequent sequences, the fetal region of interest should be within the center of the coil. If this is not the case, the coil has to be repositioned [10]. Following scout acquisition, a series of images in the axial, sagittal and coronal planes orthogonal to the fetal body region in question are obtained. Fetal MRI is an interactive scanning procedure; each acquisition serves as a scout for the subsequent one in order to avoid misregistration caused by fetal movement. Imaging protocols have to be adapted to the suspected pathology as well as the gestational age. When evaluating the fetal brain, images should be obtained with a slice thickness of 3 mm in all 3 orthogonal planes. Examination of the other fetal organs can be performed with a section thickness of 4 mm. To reduce potential signal intensity loss due to cross-talk between sections, it is recommended that SSFSE sequence be acquired in an interleaved fashion with a gap equal to the section thickness [8,10]. Though respiratory triggering is useful in decreasing motion, SSFSE images can be acquired during free maternal breathing too [8]. Due to increase in resolution, smaller field of view (FOV) is preferred in fetal imaging. However, FOV should be adjusted to the increase/decrease in the fetus and/or maternal dimensions, or when aliasing artifact is problematic [8]. Although intravenous gadolinium-based contrast agents have not been found to cause any harm to the fetus [15], these have not been FDA approved for their use during pregnancy. Until the safety of gadolinium-based contrast materials in pregnant patients is established, they are not recommended in fetal MRI. General limitations of fetal MRI include the high cost, limited availability, MRI-specific absolute contraindications such as maternal pacemakers and ferromagnetic implants, and claustrophobia [1,8]. In our experience, claustrophobia is however a minor problem when the patient is adequately instructed and comforted during the examination which typically lasts about 30 min. No maternal sedation or fetal sedation/paralysis is necessary in fetal MRI. Interpretation of fetal MRI For proper interpretation of fetal MRI, a radiologist and clinician should be familiar with the normal developing fetal anatomy (Fig. 2). Fetal age (gestational age: GA) is an important factor in the depiction of fetal anatomy. Gestational age is estimated on the basis of the time of the last menstrual period compensated by the measurements on US images in weeks (WG: weeks of gestation). Interpretation of fetal MRI is discussed here using a system-oriented approach. Central nervous system For convenience, normal and abnormal developing brain is discussed under the following subheadings: cerebral parenchyma, ventricular system and midline structures, and posterior fossa. Cerebral parenchyma MRI of the normal fetal cerebrum is characterized initially by the presence of a smooth surface and large ventricles. But as the brain matures the sulci form [16]. Knowledge of the timing of appearance of sulci is important for proper interpretation of fetal brain development (Fig. 3a) [14]. The sylvian fissure begins to appear at 16 WG; the parieto-occipital and hippocampal sulci begin to appear at 22 WG. The cingular and calcarine begins to appear at 24 WG; the central sulcus start to appear from 26th WG. At 27 WG, the marginal, precentral, postcentral, and superior temporal sulci can be visualized. The superior and inferior frontal sulci appear from the 29th week of gestation. The inferior temporal and collateral sulci are first seen at 33 WG [16]. As early as 34 weeks WG, sulcation is complete and appears similar to that in an adult (Fig. 3b) [8,16,17]. Different layering patterns are observed in fetal brain MRI, depending on the age of the fetus. Early in gestation, cerebral parenchyma is differentiated into three layers: the germinal matrix, the cortical plate, and the intermediate layer. The germinal matrix appears as a dark band that outlines the lateral ventricles on T2-weighted MR images (Fig. 3a). Like the germinal matrix, the cortical plate appears as a dark band on the T2-weighted images and bright on T1-weighted images (Fig. 1). The intermediate zone appears relatively bright on the T2-weighted images, and dark on the T1-weighted images. The multilayered MR pattern of the brain parenchyma corresponds to cellular migration [17]. At 24–27 WG and later, the germinal matrix disappears resulting in the differentiation of only two layers [8,17]. Myelin can be seen at 22–40 WG [12]. Cortical malformations are identified in MRI by noting alteration of the normal sulcation pattern from a fetus particular gestational age. They may be identified as too many sulci in a less mature fetus (as in polymicrogyria), or too few (as in lissencephaly) or abnormally deep or abnormally located sulci (as in schizencephaly) in a more mature fetus [2,8,16]. However, in order for the diagnosis of lissencephaly to be made using MRI, the examination must be undertaken late in pregnancy at least after 30 WG when most of the primary sulci are already present. Thin MR slices should be obtained in several planes so not to miss focal cortical malformations as in schizencephaly [16]. Fetal cerebral parenchymal abnormalities include hemorrhage, gliosis and white matter edema. Hemorrhage in utero does not seem to behave any differently from what is understood postnatally. The good contrast resolution of MRI allows detection of small intraparenchymal hemorrhages. On T1-weighted sequence, hemorrhage can appear as high signal intensity. While T2-weighted sequence may reveal hypointense hemorrhage secondary to intra- or extra-cellular met hemoglobin (Fig. 4) [8]. Gliosis and white matter edema appear as T2-hyperintense and T1-hypointense lesions. DWI will facilitate detection of white matter changes at an earlier stage in a more objective manner [16]. Ventricular system and midline structures The fetal cerebral lateral ventricles show physiologic disproportionate enlargement of the occipital horns in relation to the frontal horns that remains until 23 WG; thereafter they gradually become smaller [18]. The standard measurement of the cerebral ventricle is obtained in an axial plane through the atrium [18,19]. Ventriculomegaly is diagnosed when the width of atria measures more than 10 mm [18]. Congenital ventriculomegaly is a heterogeneous disease for which genetic, infectious, ischemic, and neoplastic causes have been implicated [20]. Because the prognosis of fetal ventriculomegaly is worse in presence of additional abnormalities, the prenatal detection of such abnormalities is critical [19]. MRI has an important role as an adjunctive tool to sonography in the evaluation of ventriculomegaly; it can rule out the diagnosis, confirm the finding or add associated abnormalities not amenable to sonographic diagnosis. Sonographically-occult findings include developmental abnormalities (such as agenesis of the corpus callosum, cortical malformations, cerebellar dysplasia, Walker–Warburg syndrome, and ponto-cerebellar dysplasia), as well as destructive abnormalities (such as a periventricular leukomalacia, porencephaly and subependymal hemorrhage) (Fig. 4) [2,8]. Fetal MRI can be helpful in assessing the shape of the entire ventricular system [20]. The margins of the lateral ventricles should be carefully scrutinized for any areas of nodularity that may represent periventricular nodular heterotopias or subependymal tubers in tuberous sclerosis [8]. The corpus callosum can be detected on the midline sagittal T2-WI as a C-shaped hypointense structure at the superior margin of the cavum septum pellucidum [1]. Anomalies of the corpus callosum include hypoplasia, complete or partial agenesis. The midsagittal fetal MR image enables direct visualization of the corpus callosum and diagnosis of complete or partial agenesis anomalies (Fig 5) [8]. Axial and coronal MR images can provide indirect signs of complete agenesis of corpus callosum such as absent cavum septum pellucidum, straight parallel lateral ventricles, dilated occipital horns of lateral ventricles (colpocephaly), high riding third ventricle, and unformed cingulate sulcus [2]. Fetal MRI is useful in diagnosing dysplastic/agenetic septum pellucidum and any associated anomalies related to optic chiasm or pituitary as part of septo-optic dysplasia [19]. Holoprosencephaly is a midline brain anomaly characterized by variable severity of non-cleavage of cerebrum, agenesis of corpus callosum, and associated mid facial anomalies [8]. Posterior fossa Fetal MRI can determine the global volume of the posterior fossa and show the position of the tentorium cerebelli (Fig. 5). It enables a morphological and biometrical analysis of the posterior fossa structures [20,21]. The cerebellar vermis is best seen on direct midline sagittal and coronal images. The cerebellar hemispheres are best assessed on non-oblique axial and coronal views. Measurements can be made and compared with established norms [8]. Significant reduction of the transverse cerebellar diameter (TCD) is seen in cerebellar hypoplasia. Due to cranio-caudal development of the vermis in embryogenesis, partial agenesis is always inferior. In the presence of a proband, MRI at 20–22 WG is recommended to rule out the possibility of vermian agenesis recurrence. The malformation can affect the vermis or hemispheres and potentially the brainstem. Involvement of the brainstem is diagnosed by the absence of the anterior pontine flexure resulting in a flat pons (Fig. 6) [21]. Joubert syndrome and related cerebellar disorders (JSRD) can be diagnosed by fetal MRI as early as the 17th–18th weeks of gestation by identifying molar tooth sign (MTS) [22]. MTS is s sign that results from a combination of midbrain, vermian, and superior cerebellar peduncle abnormalities (Fig. 7) [23]. However, in all of the previously discussed cases, the posterior fossa is normal in size and the tentorium cerebelli is in the correct position [21]. The cisterna magna is an important landmark in the posterior fossa. Detection of an enlarged cisterna magna (>10 mm) should prompt a detailed examination of the fetal brain [22]. Dandy Walker continuum describes a spectrum of anomalies of the posterior fossa that are diagnosed by an enlarged cisterna magna and include: mega cisterna magna (normal 4th ventricle, vermis and tentorium); Blake’s pouch cyst (cystic dilatation of the 4th ventricle, normal vermis, and normal tentorium); vermian hypoplasia (cystic dilatation of the 4th ventricle, hypoplastic vermis, and normal tentorium); and Dandy-Walker malformation (DWM) (cystic dilatation of the 4th ventricle, hypoplastic vermis, and superior displacement of the tentorium) (Fig. 8) [19–21,24]. Obliteration of the cisterna magna is the most consistent finding in Arnold-Chiari malformation. The most common forms of Chiari malformation are the types I and II. Chiari I consists of downward herniation of the cerebellar tonsils. In Chiari II, the posterior fossa is small with herniation of the inferior part of the vermis and fourth ventricle, hypoplastic cerebellar hemispheres and usually supratentorial ventricular dilatation. Obliteration of the cisterna magna should suggest a spinal defect as myelomeningocele is always associated with Chiari II malformation (Fig. 9) [20,22,23]. Spine The entire length of the fetal spine could be studied in multiple planes on MRI. Evaluation of the spinal column is thus important to detect abnormalities such as neural tube defects (NTDs). NTD are a heterogeneous group of malformations resulting from failure of normal neural tube closure early in embryologic development. NTD include anencephaly, cephalocele, spina bifida, and less commonly iniencephaly [9,25]. Spina bifida is a defect of the vertebrae resulting in exposure of the contents of the neural canal. Similarly, cephaloceles are diagnosed when contents protrude through a skull defect. MRI shows well the location and extent of the bony defect as well as the size and contents of the protruding sacs. [19,21]. Face and neck The fetal face is an important part of antenatal structural survey. Facial malformation may indicate an underlying chromosome abnormality or syndrome [26–28]. Three-dimensional US technique has been used to generate accurate detailed images of the facial surface anatomy [26]. Using the three orthogonal planes, MRI can help US in assessment of complex craniofacial deformities such as holoprosencephaly and craniosynostosis (Figs. 10 and 11) [29]. MRI enables visualization of the internal anatomy including the oral and hypo-pharynx. The fetal airway is fluid-filled and therefore appears bright on T2-weighted images (Fig. 10a). Because of possible life threatening airway obstruction, the identification of neck masses in utero is crucial determinant of method and location of delivery. MRI demonstrates the relationship of the masses to the neck, airway and mediastinum [26]. This has been of emerging importance as the ex utero intrapartum treatment (EXIT) and fetal surgery are increasingly being used to manage these fetuses [27]. The most common fetal neck masses are teratomas and goiters, anteriorly, and cystic hygromas, posterolaterally [26]. MRI is useful in differentiating goiter form other anterior neck masses (e.g. teratoma and hemangioma) because of the characteristic signal intensity of the thyroid being hyperintense on T1- and isointense on T2-weighted images. Ultrasonography is the modality of choice for diagnosis of cystic hygromas in-utero; however, fetal MRI can be useful in assessment of infiltration of the cysts into the surrounding structures (Fig. 12) [26–28]. The differential diagnosis of an extracranial cystic mass in the posterior neck region includes cystic hygroma or meningo-encephalocele [3,26]. A prerequisite for the diagnosis of encephalocele in contrast to nuchal cystic hygroma is the demonstration of an associated bony defect in the skull and protrusions of the brain. MRI provides exquisite detail of both the cranial defect and the herniated contents [24,25]. Thorax The normal fetal lungs have homogeneous moderately high signal intensity on T2-weighted images. With increasing maturation, the fetal lungs show increase in volume and in T2-signal. Sagittal and coronal images at the level of the diaphragm clearly show the distinction between the structures of the thorax and those of the abdomen [29]. The most common masses within the fetal chest are congenital cystic adenomatoid malformation (CCAM), broncho-pulmonary sequestration, congenital diaphragmatic hernia (CDH), and hydrothorax. Congenital chest masses have characteristic MR appearances. On fetal MRI, CCAM appearance varies depending on whether the lesions are microcystic or macrocystic (Fig. 13) [30]. CCAM may consist of few large cysts (type I) or more numerous smaller to moderate sized cysts (type II) of increased T2-signal intensity arising from any lung lobe. Microcystic CCAM (type III) typically demonstrates homogeneous moderately high signal intensity on T2-weighted signal that could be indistinguishable from bronchopulmonary sequestration in the absence of a visible feeding artery from the aorta to suggest the diagnosis of sequestration [30,31]. CDH occurs most commonly in the posterior aspect of the left hemi-diaphragm due to failure of formation of the diaphragmatic leaflets. The presence of liver in the chest in fetuses with left sided CDH markedly worsens the prognosis. MRI allows direct visualization of the position of the liver and differentiates meconium-filled herniated bowel loops form cystic lesions within the chest [3,32]. Assessment of fetal lung development with MRI has been particularly pertinent to the management of conditions as chest masses in which prognosis is closely related to the severity of pulmonary hypoplasia. Marked reduction of signal intensity as well as lung volumes are characteristic MR findings in fetuses with pulmonary hypoplasia [31]. It is complicated to visualize the fetal heart with MRI owed to its small size and high pulsation rate. Depicting fetal heart and vessels depend on the MR sequence used (Fig. 14). With SSFSE T2-weighted images, the heart and vessels are demonstrated as flow void that contrasts well with the hyperintense surroundings [30]. Balanced steady state free precession sequences, as true-FISP or b-FFE, are superior in visualizing the heart and vessels demonstrated as hyperintense structures. MRI protocol for studying the fetal heart along body and cardiac planes has been introduced recently [11]. Fetal MRI shows potential value in detecting cardiac abnormalities without the need of sedation or fetal cardiac gating. Fetal MRI can identify positional anomalies of the heart, cardiac malformations associated with cardiomegaly, different sizes of the cardiac chambers, and cardiac tumors. Malformations of the great vessels and atrioventricular canal defects can be visualized in larger fetuses by fetal MRI (Fig. 15) [33]. More studies are needed to develop fetal MRI cardiac triggering and advance dynamic sequences needed for evaluation of the anatomical and functional aspects of fetal cardiac pathologies. Abdomen and gastrointestinal tract On T2-weighted images of fetal abdomen, organs such as the esophagus, stomach, intestine, urinary collecting systems, and bladder appear hyperintense because of the fluid they contain [29]. The meconium is produced after 13 WG and slowly migrates from small bowel to colon. Due to functional obstruction of the anal canal at 20 WG, meconium progressively accumulates in the bowel. The proximal intestine appears hyperintense on T2- and hypointense on T1- weighted images being formed mainly of ingested amniotic fluid. The colon contains meconium with high protein and minerals content; it appears hypointense on T2- and hyperintense on T1-weighted images [29,30,34]. Identification of meconium in the colon on T1-weighted images can aid in the diagnosis of complex fetal abnormalities (Fig. 16) [34]. The bowel diameters increase with advancing age. At 20 WG small bowel measures 2–3 mm and large bowel 3–4 mm in diameter. By 35 WG, small bowel measures 5–7 mm and large bowel 8–15 mm in diameter [32]. Through recognition of the caliber and signal changes of small and large bowel, MRI can diagnose bowel atresia and locate the level of bowel obstruction with widely dilated bowel loops proximal to the site of stenosis [30]. On MRI, abdominal organs, and meconium-filled extracorporeal small intestines can be identified in gastroschisis and omphalocele (Fig. 17) [30,34,35]. Early in fetal life the majority of erythropoiesis occurs in the fetal liver. The liver shows high signal on T1- and low signal on T2-weighted images secondary to increased iron content from fetal hemoglobin; protein, copper, and zinc likely contribute to the increased T1-signal intensity of the liver [29,30,36]. The spleen is detectable by 20 WG; it shows homogeneous signal that decreases with advancing gestation on T2-weighted images [29,37]. The gall bladder, a cystic structure under the lower aspect of the live, could be demonstrated from 18 WG onward. The biliary ducts cannot usually be demonstrated under normal conditions [32]. Fetal MRI can assess cystic masses related to the liver. The differential diagnosis of an intrahepatic cyst includes congenital liver cyst, choledochal cyst, biliary atresia or duodenal duplication. Congenital hepatic cyst is usually unilocular and, unlike choledochal cyst, does not communicate with the biliary system (Fig. 18) [37,38]. Genitourinary system The length, signal intensity on T2-weighted images, and apparent diffusion coefficient (ADC) of the fetal kidney change significantly with gestational age [39]. Renal cortex is hypointense to the medulla on T2-weighted images. Progressive increase in renal cortex/medulla signal intensity ratio with gestational age reaches its maximum at term [39,40]. The urinary bladder is easily recognized as a fluid-filled structure in the pelvis. Since the fetal pelvis is very small, the filled urinary bladder may occupy considerable portions of the abdomen in older fetuses (>30 WG) (Fig. 19) [30]. MRI can show morphological features of urinary diseases as cystic lesions of the kidneys (Fig. 20), obstructive uropathy (e.g. posterior urethral valve) (Fig. 21), renal tumors, and urinary tract anomalies [40]. Though differentiation of renal cysts from a dilated collecting system can sometimes be difficult, central cystic lesions are more likely to be dilatation of the collecting system, whereas lesions at the periphery are more likely to be renal cysts [40,41]. The dysplastic fetal renal parenchyma shows increased signal intensity on T2-weighted images produced by cystic dilatation of the collecting tubules [30,40]. A helpful clue to the diagnosis of a dysplastic kidney is missing of the normal bright signal on ADC images of DWI [41]. The scrotum and penis are often recognized in the male fetus. MRI proved to be an excellent technique for revealing different fetal genital diseases as ovarian cysts and hypo-/epi-spadia [40]. MRI aids also in assessment of the fetal perineum which is helpful in the fetuses with cloacal exstrophy and in cases in which gender is an important consideration for diagnosis [33,40,41]. Musculoskeletal system and fetal organ volume Fetal MRI can assess the skeleton and muscles owed to the innovations in MRI sequence technology such as echoplanar imaging (EPI), thick slab T2-Weighted, and dynamic sequences. Ultrasonography, particularly three-dimensional imaging, remains the method of choice in measuring bones and observing abnormal fetal skeletal anomalies such as club foot or abnormal fingers [29]. Fetal MRI can help in diagnosing complex musculoskeletal abnormalities through careful assessment of the whole fetus and detection of associated abnormalities [41]. Echoplanar MR imaging (EPI) are useful to obtain an overview of thoracic size and skeletal development [32]. MRI can detect fetal surface contours, and assess the integrity of the body wall [2]. Fetal MRI can estimate organ volumes such as lung volume which enables prediction of outcome in fetuses at risk for pulmonary hypoplasia especially in the third trimester of pregnancy [31,42,43]. Pregnancy-related structures Evaluation of the placenta, umbilical cord and amniotic sac is part of the fetal MR examination. The T2-weighted MR images show the placenta as a moderately hyperintense structure. Prenatal MRI of the normal placenta shows morphological changes during gestation (Fig. 22). At 19–23 WG, placenta has regular homogeneous structure. With advanced gestation, placenta shows increase in lobules number and T2-signal intensity. The placenta/amniotic fluid signal ratio significantly decreases with advanced gestation. Moreover, the visual difference between the inner lobular and homogeneous placental tissue are increasingly marked with ongoing placental maturation [44]. During the placental aging, venous stasis and/or thrombotic changes may cause areas of normal placental infarctions that appear as map-like changes [45,46]. Multiplanar MR images allow detailed assessment of placental insertion defects and tumors that can guide better management [47]. The umbilical cord and its insertion are also well demonstrated in MRI [48,49]. Amniotic fluid abnormality, whether deficient (oligohydraminoms) or in excess (polyhydraminos), is usually the first clue of an underlying fetal disorder. The amniotic fluid has a low signal on T1-weighted and a high signal on T2-weighted images [48]. MRI is useful in the assessment of pregnancies complicated by oligohydramnios, which can limit the diagnostic sensitivity of US [50,51]. Role of fetal MRI in prenatal counseling of fetal anomalies Prenatal counseling helps the family to decide between prenatal therapies, postnatal therapies or the interruption of the pregnancy [52]. Through accurate demonstration of the fetal disorder, prenatal MRI can play a role in determination pregnancy prognosis and management. The additional findings provided by MRI are helpful to expectant parents and their clinicians in understanding the severity of the abnormality and reaching an informed decision regarding pregnancy continuation or termination [22,25,53]. Role of fetal MRI in supporting in-utero surgery Fetal MRI can facilitate management decisions and guide therapy when fetal surgery is a consideration or when delivery is expected to present unique challenges [54,55]. Conditions in which fetal MRI appears to contribute to fetal surgical planning and postoperative evaluation include congenital diaphragmatic hernia, cystic adenomatoid malformation, myelomeningocele, complicated twin pregnancies, upper airway obstruction, and sacrococcygeal teratoma [3,54,55]. Sacrococcygeal teratoma is the most common congenital neoplasm; its high perinatal mortality and morbidity rates seem to be related to the content and extent of the mass rather than to its size [56,57]. The impact of fetal MRI on the management of sacrococcygeal teratoma is discussed as an example (Fig. 23). Fetal MRI provides important multiplanar images that may obviate the need for early postnatal imaging [4]. MR images are more easily understood by surgeons and other clinicians resulting in more accurate prenatal counseling and improved preoperative planning for surgical resection [58]. Role of fetal MRI in supporting research studies In addition to the clinical indications, MRI is used in research studies of normal and abnormal human fetal development [59]. Research studies of MRI of normal fetuses at different gestational ages allow establishing of normative measures that can be used in early identification of developmental abnormalities [22,60,61]. The significant technical progress in fetal MRI sequences, such as Diffusion Tensor imaging and functional MRI, as well as the capability of formation of 3-D images may open the door for future studies of fetal development and gene therapy [14,62–64]. Conclusions MRI allows excellent detailed visualization of the fetus in utero as well as the pregnancy structures. By using a systematic approach, fetal MRI is useful in the recognition of the developing fetal anatomy, detection of subtle fetal abnormalities and evaluation of complex lesions. Prenatal MRI can facilitate management decisions and guide therapy, particularly when fetal surgery is a consideration or when delivery is expected to present unique challenges. Conflict of interest The author has declared no conflict of interest. Compliance with Ethics Requirements The author declares no potential conflicts of interest with respect to the manuscript authorship, and/or publication of this article. The author received no financial support for the manuscript authorship and/or publication of this work. No ethical approval was required for preparation and publication of this article by Institute’s Medical Research Ethics Committee (REC).
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              Midgut volvulus causing fetal demise in utero.

              Intestinal malrotation has an incidence of 1 per 6000 live births. The most serious consequence of malrotation is volvulus. Midgut volvulus is a rare condition in which the small bowel and proximal colon twist around the superior mesenteric artery, leading to a high-grade proximal bowel obstruction and vascular compromise of the intestine, thereby leading to infarction of the involved intestine. Midgut volvulus rarely occurs antenatally and is usually not lethal in utero. There are only 7 cases of intrauterine fetal demise caused by midgut volvulus reported in the literature. We report a case of intrauterine fetal demise at 38 weeks of gestation, due to cardiovascular failure and shock from midgut volvulus. Non-specific abnormalities, including ascites and dilated bowel, had been seen on the antenatal ultrasound from the 15th week of gestation. In addition to the volvulus, the fetus had intestinal atresia and arthrogryposis.
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                Author and article information

                Journal
                AJP Rep
                AJP Rep
                10.1055/s-00000169
                AJP Reports
                Thieme Medical Publishers (333 Seventh Avenue, New York, NY 10001, USA. )
                2157-6998
                2157-7005
                April 2016
                : 6
                : 2
                : e239-e242
                Affiliations
                [1 ]Division of Emergency Medicine, Department of Pediatrics, Nationwide Children's Hospital, Columbus, Ohio
                [2 ]Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Connecticut Health Center, Farmington, Connecticut
                [3 ]Division of Neonatology, Department of Pediatrics, Connecticut Children's Medical Center, Hartford, Connecticut
                [4 ]Department of Pediatric Surgery, Connecticut Children's Medical Center, Hartford, Connecticut
                Author notes
                Address for correspondence Naveed Hussain, MBBS, MD, DCH Connecticut Children's Medical Center University of Connecticut School of Medicine 263 Farmington AvenueFarmington, CT 06030-2948 Hussain@ 123456uchc.edu
                Article
                160033
                10.1055/s-0036-1584548
                4983723
                27551577
                b4f7a1d1-4bba-449c-ae34-7fd28898f78f
                © Thieme Medical Publishers
                History
                : 20 April 2016
                : 16 May 2016
                Categories
                Case Report

                internal hernia,midgut volvulus,mri
                internal hernia, midgut volvulus, mri

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