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The role of fetal brain magnetic resonance imaging in current fetal medicine
Book - Dissertation
Fetal MRI has become an important adjunct to prenatal ultrasound in the assessment of fetal abnormalities, and certainly so abnormalities of the central nervous system. Although initially perceived as competing modalities it has become clear that both modalities should complement each other where indicated, permitting better understanding of the disease process, classification of abnormalities, and determination of prognosis and management options. Over the last decades several in utero treatment options have been proven beneficial and effective, including laser coagulation in complicated monochorionic pregnancies, in utero closure of spina bifida aperta and most recently fetoscopic endoluminal tracheal occlusion (FETO) in congenital diaphragmatic hernia.Because of the efficacy of fetal surgery for spina bifida aperta, accurate prenatal imaging of fetuses with spina bifida aperta has become a need to select fetuses eligible for fetal surgery. In chapter 4 we demonstrated the reliability of MRI in measuring the posterior fossa dimensions as well as the changes in these within 7 days after fetal surgery. In Chapter 5 we described the range and prevalence of supratentorial anomalies on MRI in fetuses with open spina bifida eligible for fetal surgery (Chapter 5). Despite the availability of ultrafast sequences, fetal motion is limiting the image quality. With the use of post-processing techniques it is now possible to create motion-free 3D image volumes compared to the acquired image stacks with lower resolution. In chapter 6 the post-processing and segmentation of these volume allowed us to demonstrate differences in the fetal brain volume and shape of fetuses with open spina bifida before and after fetal surgery, in comparison to normal controls. Several fetal MRI atlases of fetuses with normal fetal brain development are available, yet brain development in fetuses with open spina bifida is altered, first because of the defect and again that course may change after fetal surgery. In chapter 7 we developed a spatio-temporal atlas based on fetal MRI volumes demonstrating the pre- and postoperative brain development in fetuses with open spina bifida.Another target group of fetal surgery candidates are selected fetuses with congenital diaphragmatic hernia. Because infants with CDH are known to be at risk for significant neurodevelopmental delay, we wanted to investigate if those fetuses would have already in utero altered brain development when compared to normal controls. We found a significant difference in brain development at 28 weeks of gestation, which is the time point fetal surgery typically is offered. (chapter 8).Fetuses infected with cytomegalovirus (CMV) in the first pregnancy are also known to be at risk of neurodevelopmental delay. However the relation between prenatal brain abnormalities on imaging, and later neurocognitive impairment remain incompletely understood. In chapter 9 we demonstrated there is a correlation between the grading performed on ultrasound and fetal MRI, but the latter imaging method is more performing. Furthermore, we found significant differences on diffusion weighted imaging in several brain regions of CMV-infected fetuses compared to non-CMV-infected fetuses.Monochorionic diamniotic pregnancies complicated by twin-to-twin-transfusion syndrome (TTTS) are preferentially treated with laser coagulation of the anastomoses; in selected cases fetal reduction by cord occlusion may be chosen. Because fetuses from a complicated MC twin pregnancy are at increased risk of antenatal brain lesions, we routinely offer third trimester MRI to fetuses having undergone surgery. The prevalence of brain lesions detected by fetal MRI turned out to be higher compared to prenatal ultrasound alone (Chapter 10). Therefore, fetal MRI in the third trimester seems to be a useful adjunct after in utero surgery for TTTS.