Fetal imaging of central nervous system abnormalities

Injury of the developing cerebellum: a brief review of the effects of endotoxin and asphyxial challenges in the late gestation sheep fetus

The vulnerability of the fetal and newborn brain to events in utero or at birth that cause damage arising from perturbations of cerebral blood flow and metabolism, such as the accumulation of free radicals and excitatory transmitters to neurotoxic levels, has received considerable attention over the last few decades. Attention has usually been on the damage to cerebral structures, particularly, periventricular white matter. The rapid growth of the cerebellum in the latter half of fetal life in species with long gestations, such as the human and sheep, suggests that this may be a particularly important time for the development of cerebellar structure and function. In this short review, we summarize data from recent studies with fetal sheep showing that the developing cerebellum is particularly sensitive to infectious processes, chronic hypoxia and asphyxia. The data demonstrates that the cerebellum should be further studied in insults of this nature as it responds differently to the remainder of the brain. Damage to this region of the brain has implications not only for the development of motor control and posture, but also for higher cognitive processes and the subsequent development of complex behaviours, such as learning, memory and attention.

The clinical relevance of fetal MRI in the diagnosis of Type IV cystic sacrococcygeal teratoma--a review

The introduction of fetal magnetic resonance imaging (MRI) has improved the prenatal evaluation of uterine, placental and fetal anatomy. However, its utilization has mostly been restricted to fetal central nervous system anomalies. We review how adjunct fetal MRI was performed and diagnosis of cystic type IV sacrococcygeal teratoma was made. We also discuss the clinical relevance of fetal MRI in differentiating this lesion from other selected abdominal/pelvic cystic malformations and lesions.

MRI of the foetal brain using a rapid 3D steady-state sequence

OBJECTIVE

To evaluate the capacity of a rapid T2 weighted three-dimensional (3D) sequence to diagnose foetal brain abnormalities by comparing the results with current two-dimensional (2D) methods. We have also made assessments of the estimates of energy deposition using those methods.

METHODS

50 pregnant females were included in this study under the guidance of the institutional review board. All their foetuses had suspected brain abnormalities on antenatal ultrasonography or were at increased risk of a brain malformation based on the results of an earlier pregnancy. All the foetuses had a routine MR protocol that includes three orthogonal plane single-shot fast-spin echoes and 2D steady-state sequences. In addition, a 3D rapid steady-state sequence of the foetal brain was performed (acquisition time approximately 40 s), and the standard and 3D sequences were reported independently and the results were compared. The specific absorption rate (SAR) predicted by the scanner was recorded in 12 cases in order to estimate the energy deposited by the three sequences.

RESULTS

The 3D rapid steady-state sequences produced diagnostic-quality images in 41/50 (82%) cases. All the failures were in second trimester foetuses (9/26-35% failure rate). There was a discrepancy between the standard report and findings using the 3D sequence in 2/41 of the foetuses with good-quality 3D imaging. The predicted SAR deposition of the 3D steady-state sequences was comparable with the single-shot fast-spin echo sequence.

CONCLUSION

Our initial assessments of a 3D rapid steady-state sequence to image the foetus are encouraging in terms of diagnostic information and acceptable energy deposition values. The high failure rate in second trimester foetuses probably relates to the greater mobility of the smaller foetuses, and improvements in the 3D sequence are required in terms of reduced acquisition time and higher resolution.

ADVANCES IN KNOWLEDGE

We have shown that 3D T2 weighted images of the foetal brain can be acquired in a clinical setting and produce diagnostic-quality imaging in a high proportion of cases. The success rate in acquiring diagnostic-quality images is related to gestational age. Good-quality images were obtained in all third trimester foetuses but only in approximately two-thirds of second trimester foetuses. This probably reflects the problem of the greater mobility of second trimester foetuses. 3D T2 weighted acquisitions have great potential for improving the antenatal diagnosis of foetal brain abnormalities and may reduce the time that a pregnant female needs to spend on the MR scanner.

The use of in utero MRI to supplement ultrasound in the foetus at high risk of developmental brain or spine abnormality

OBJECTIVES

It is widely accepted that the diagnosis of foetal central nervous system (CNS) abnormalities can be improved by performing MRI examinations in utero. Most of the published literature has concentrated on pregnancies in which a developmental abnormality has been detected (or suspected) on ultrasound in an otherwise low-risk pregnancy. In this paper, we test the hypothesis that in utero MRI of the foetal brain in high-risk pregnancies will detect abnormalities not shown by ultrasound at a rate that justifies its use in clinical practice.

METHODS

100 females were recruited into the study from foeto-maternal or clinical genetic departments. They all had a foetus/child with a CNS malformation from an earlier pregnancy, which led to an increased risk of recurrence being quoted for the present pregnancy. All in utero MRI examinations were performed on 1.5 T clinical MRI systems at 18 weeks gestational age or later.

RESULTS

In 78% of cases, the ultrasound and MRI results agreed and showed no abnormality. In 13%, ultrasound and MRI described identical abnormal findings. In 9%, the ultrasound and MRI examinations had discrepant findings; in all these cases the MRI findings described more serious CNS pathology. The effects on management were judged to be major, by at least one assessor, in 7/9 of those cases.

CONCLUSION

As in many other situations involving antenatal detection of CNS abnormalities, in utero MRI should be considered in females with increased risk of foetal CNS malformation based on the results of an earlier pregnancy. Advances in knowledge In utero MRI of the foetus has an important role in antenatal diagnosis of females carrying a foetus with an increased risk of a brain abnormality.

The use of in utero MR imaging to delineate developmental brain abnormalities in multifetal pregnancies

BACKGROUND AND PURPOSE

iuMR has been shown to increase the detection rate of developmental abnormalities of the CNS, though most reports are limited to singleton pregnancies. The hypothesis tested in this study was that iuMR performed in multifetal pregnancies will show additional information about fetal CNS abnormalities in a similar proportion of cases when compared with singleton pregnancies.

MATERIALS AND METHODS

Fifty women with multifetal pregnancies were recruited consecutively carrying at least 1 fetus with a suspected developmental fetal CNS abnormality on sonography. All had iuMR at the same center by using the same MR imaging protocol. When the sonography and MR imaging reports were discrepant, 1 fetomaternal expert assessed the reports independently to predict in what percentage a change in prognosis/counseling would have occurred if iuMR was included in the diagnostic pathway.

RESULTS

There was agreement between the sonography and iuMR reports in 66% and disagreement in 34% of cases. The major cause for discrepancy was the presence or absence of the corpus callosum, which accounted for 10/17 of the disagreements. In 12/17 of the discrepant cases, the effect on management was judged to be significant.

CONCLUSIONS

We conclude that iuMR has a similar rate of discrepancy to sonography in multifetal pregnancies compared with the published data concerning singleton pregnancies. Our analysis of the effect on management shows that changes in the decision to consider termination of pregnancy would have occurred in 12/17 of the discrepant cases (ie, in 24% of our cases overall).

Fetuses with ventriculomegaly diagnosed in the second trimester of pregnancy by in utero MR imaging: what happens in the third trimester?

BACKGROUND AND PURPOSE

Although MR imaging of the fetal brain has been shown to provide additional diagnostic information, the optimal timing of the study and the value of repeat studies remain unclear. The primary purpose of this study was to look for structural abnormalities of the fetal brain shown at 30-32 weeks' gestational age but not on the 20-24 weeks' study in fetuses originally referred with isolated VM. In particular, we wished to study the hypothesis that third-trimester fetal MR imaging studies would not show extra brain abnormalities compared with the second-trimester studies in this group.

MATERIALS AND METHODS

Ninety-nine women were admitted for a fetal MR study between 20-24 weeks' gestational age, and 46 of these women agreed to return for a second MR imaging examination at 30-32 weeks' gestational age. The other women were either lost to follow-up or declined the invitation to return. Two experienced observers measured the width of the trigones, and the results were compared, to test reliability. Changes in the degree of VM are reported along with changes in the diagnosis of structural brain abnormalities.

RESULTS

There was excellent reproducibility of trigone measurements between the 2 observers, with a mean absolute difference of <1 mm in the 40 fetuses that were ultimately shown to have isolated VM. Twenty-eight of 40 fetuses studied had mild VM on the first iuMR imaging examination, but in just more than half, the category of VM changed between the studies (5 had become normal-sized, 7 had progressed to moderate, 3 had become severe, and 13 remained mild). In 1 case, hypogenesis of the corpus callosum was recognized at 30-32 weeks but had not been reported on the 20-24 weeks' examination; the other 5 fetuses had brain pathology recognized on both fetal MR studies.

CONCLUSIONS

Trigone measurements can be made in a highly repeatable fashion on iuMR imaging. We have not shown any major advantage in repeating iuMR imaging at 30-32 weeks' gestation in terms of improved diagnosis of other structural brain abnormalities. With the converse of that argument, however, our data suggest that there is no advantage in delaying iuMR imaging studies to 30-32 weeks in the hope of improving detection rates.

A prospective study of fetuses with isolated ventriculomegaly investigated by antenatal sonography and in utero MR imaging

BACKGROUND AND PURPOSE

Fetal ventriculomegaly (VM) is important because of its high prevalence and high risk of association with other brain abnormalities. The purpose of this article was to investigate the hypotheses that including in utero MR imaging (iuMR) in the diagnostic pathway for fetuses with isolated VM on antenatal imaging will show other brain abnormalities in a high proportion of cases and that these will have a significant effect on clinical management.

MATERIALS AND METHODS

One hundred forty-seven pregnant women were recruited prospectively from 8 fetomaternal centers in Britain. All of the fetuses had VM diagnosed on sonography but no other abnormality. iuMR was performed, and the results of the examinations were compared with those of sonography. Two fetomaternal experts made independent assessments of the effects of any new diagnoses on clinical management.

RESULTS

Categoric assessments of ventricular size were the same in approximately 90% of fetuses. Other abnormalities were shown in 17% of fetuses. The most frequent additional brain abnormality shown on iuMR was agenesis of the corpus callosum. Severe VM was associated with an approximately 10-fold increase in the risk of another brain abnormality being present when compared with fetuses with mild VM. The most profound effects on clinical management, however, were found in cases of mild VM.

CONCLUSIONS

This work supports our hypotheses by showing a high detection rate of other brain pathology when iuMR was used to supplement antenatal sonography (17%). In a high proportion of cases, the detection of the extra pathology would have led to significant changes in clinical management.

The fetus that is small for gestational age

The symmetric small for gestational age (SGA) fetus presents a complex management problem for the obstetrician, but the growth restriction affects morbidity and mortality at all stages of life. The differential diagnosis in symmetric growth aberration includes the constitutionally small fetus, the fetus with pathology, and the cases with incorrect dating of pregnancy. The ultrasonographic examination focuses in the detection of anomalies, signs of intrauterine infection, and serial assessment of fetal growth. Accuracy of fetal biometry may be improved by using individualized fetal growth curves. From the available surveillance tools, the uterine artery Doppler has a value in predicting poor perinatal outcome. Magnetic resonance imaging is also useful in the evaluation of anomalies. Cesarean section is not justified for all symmetric SGA fetuses that may carry a guarded prognosis.

Neuroimaging of the child with developmental delay

Developmental delay (DD) affects approximately 1% to 3% of all children in the United States. This diagnosis significantly impedes quality of life and full participation in the life of the family, school, and community. In this setting, the clinician's ability to detect, diagnose, and possibly treat the cause for DD in a timely manner depends on a multimodality approach to neuroimaging and a robust understanding of the various imaging algorithms aimed at determining the etiology of disease, structural and/or anatomic defects, functional activity, metabolic profiles, and genetic characteristics. Taken separately and in combination, these features are effectively depicted and analyzed using an array of brain imaging modalities: ultrasound, computed tomography, nuclear medicine, magnetic resonance (MR) spectroscopy, and a growing mix of sophisticated MR imaging (MRI) techniques, including diffusion-weighted imaging, diffusion tensor imaging, perfusion MRI, and functional MRI. Thus, equipped with these advanced imaging capabilities, pediatric neurologists and neuroradiologists are now positioned to diagnose with greater accuracy and speed; this, in turn, results in more effective treatment plans and improved patient outcomes as measured by progress in reaching developmental milestones and in ameliorating secondary conditions such as seizures, poor motor control, incontinence, and impulsivity. The purpose of this article is to present the numerous causes of pediatric DD, describe their respective neuroimaging findings, discuss various neuroimaging approaches for elucidating etiology, and offer specific guidelines for optimizing imaging results in the setting of multimodality imaging capabilities.

MRI of the foetal brain

Ultrasound examinations for foetal brain abnormalities have been a part of the routine antenatal screening programme in the UK for many years. In utero brain magnetic resonance imaging (MRI) is now being used increasingly successfully to clarify abnormal ultrasound findings, often resulting in a change of diagnosis or treatment plan. Interpretation requires an understanding of foetal brain development, malformations and acquired diseases. In this paper we will outline the technique of foetal MRI, relevant aspects of brain development and provide illustrated examples of foetal brain pathology.

Two-dimensional fast imaging employing steady-state acquisition (FIESTA) cine acquisition of fetal non–central nervous system abnormalities

PURPOSE

To evaluate the value of two-dimensional fast imaging employing steady-state acquisition (2D FIESTA) cine MR with parallel imaging techniques in the diagnosis of fetal non-central nervous system (CNS) anomalies.

MATERIALS AND METHODS

A total of 28 pregnant women were referred for further MR evaluation on fetuses after abnormal sonographic results. A total of 33 fetal MR examinations were performed by a 1.5 T MR scanner with eight-channel phase-arrayed body coils. Single-shot fast spin-echo (SSFSE(R), GE) of three orthogonal planes and 2D FIESTA for cine fetal MR of three sagittal planes (midsagittal and 10 mm off midline on left and right) were routinely acquired. Additional planes on target organs with variable imaging frames were added if indicated.

RESULTS

Nine of the 33 examinations (9/33; 27.3%) had motion artifacts obscuring the detail in SSFSE imaging; 2D FIESTA imaging provided motion-artifact-free imaging in all of them. Cine 2D FIESTA imaging provided additional information on the visceral peristalsis. The information helped in differentiating dilated gastrointestinal (GI) tract from other intraabdominal cystic lesions and in confirming the nature and level of GI tract obstruction.

CONCLUSION

With sub-half-second temporal resolution of the 2D FIESTA sequences, fetal movement is no longer problematic. In addition to the anatomical information also provided by conventional SSFSE sequences, 2D FIESTA demonstrates information on motility and peristalsis of hollow organs and helps the diagnosis of fetal visceral anomalies.

Fetal MR Imaging

Ultrasonography is the primary prenatal screening modality used in the evaluation of the fetus and the maternal pelvis. However, fetal MR imaging plays a complementary role to prenatal ultrasound in the evaluation of the fetus with suspected abnormalities. MR imaging's role includes confirming or excluding possible lesions, defining their full extent, aiding in their characterization, and demonstrating other associated abnormalities. As newer techniques such as diffusion imaging, MR spectroscopy, and functional studies are used more widely, it is hoped that additional information will be made available by this modality to physicians evaluating and taking care of fetuses.

Diagnosis of inferior vermian hypoplasia by fetal magnetic resonance imaging: potential pitfalls and neurodevelopmental outcome

OBJECTIVE

Advances in fetal magnetic resonance imaging allow the detection of subtle anatomic anomalies of unclear long-term clinical significance. The purpose of this study was to examine the accuracy of fetal magnetic resonance imaging in the diagnosis of isolated inferior vermian hypoplasia and to describe the neurodevelopmental outcome.

STUDY DESIGN

We reviewed all cases with fetal and postnatal magnetic resonance imaging studies between 1999 and 2003 and identified 19 cases with a diagnosis of isolated inferior vermian hypoplasia. We compared prenatal and postnatal magnetic resonance imaging studies and evaluated subjects using developmental scales.

RESULTS

Isolated inferior vermian hypoplasia was confirmed by postnatal magnetic resonance imaging in 68% of the patients (13/19); the remaining 6 patients had normal postnatal magnetic resonance imaging results. On developmental testing at mean age 19.8 +/- 4.9 months, 3 infants (23%) with confirmed postnatal diagnosis demonstrated motor and language delays and functional difficulties, and 2 infants (15%) had behavioral problems; none of the infants with normal postnatal magnetic resonance imaging studies were delayed.

CONCLUSION

Isolated inferior vermian hypoplasia in the second trimester may be over-diagnosed by fetal magnetic resonance imaging and therefore warrants postnatal magnetic resonance imaging confirmation.