Abstract
To report the rate of additional central nervous system (CNS) anomalies detected exclusively on prenatal magnetic resonance imaging (MRI) in fetuses diagnosed with isolated mild or moderate ventriculomegaly (VM) on ultrasound, according to the type of ultrasound protocol adopted (dedicated neurosonography vs standard assessment of the fetal brain), and to explore whether the diagnostic performance of fetal MRI in detecting such anomalies is affected by gestational age at examination and laterality and degree of ventricular dilatation. MEDLINE, EMBASE, CINAHL and Clinicaltrials.gov were searched for studies reporting on the prenatal MRI assessment of fetuses diagnosed with isolated mild or moderate VM (ventricular dilatation of 10-15 mm) on ultrasound. Additional anomalies detected only on MRI were classified as callosal, septal, posterior fossa, white matter, intraventricular hemorrhage, cortical, periventricular heterotopia, periventricular cysts or complex malformations. The rate of additional anomalies was compared between fetuses diagnosed on dedicated neurosonography, defined as a detailed assessment of the fetal brain, according to the International Society of Ultrasound in Obstetrics and Gynecology guidelines, and those diagnosed on standard fetal brain assessment. The rate of additional CNS anomalies missed on prenatal MRI and detected only at birth was calculated and compared between fetuses that had early (at or before 24 weeks' gestation) and those that had late (after 24 weeks) MRI. Subanalysis was performed according to the laterality (uni- vs bilateral) and degree (mild vs moderate, defined as ventricular dilatation of 10-12 and 13-15 mm, respectively) of ventricular dilatation. Whether MRI assessment led to a significant change in prenatal management was explored. Random-effects meta-analysis of proportions was used. Sixteen studies (1159 fetuses) were included in the systematic review. Overall, MRI detected an anomaly not identified on ultrasound in 10.0% (95% CI, 6.2-14.5%) of fetuses. However, when stratifying the analysis according to the type of ultrasound assessment, the rate of associated anomalies detected only on MRI was 5.0% (95% CI, 3.0-7.0%) when dedicated neurosonography was performed compared with 16.8% (95% CI, 8.3-27.6%) in cases that underwent a standard assessment of the fetal brain in the axial plane. The overall rate of an additional anomaly detected only at birth and missed on prenatal MRI was 0.9% (95% CI, 0.04-1.5%) (I2 , 0%). There was no difference in the rate of an associated anomaly detected only after birth when fetal MRI was carried out before, compared with after, 24 weeks of gestation (P = 0.265). The risk of detecting an associated CNS abnormality on MRI was higher in fetuses with moderate than in those with mild VM (odds ratio, 8.1 (95% CI, 2.3-29.0); P = 0.001), while there was no difference in those presenting with bilateral, compared with unilateral, dilatation (P = 0.333). Finally, a significant change in perinatal management, mainly termination of pregnancy owing to parental request, following MRI detection of an associated anomaly, was observed in 2.9% (95% CI, 0.01-9.8%) of fetuses undergoing dedicated neurosonography compared with 5.1% (95% CI, 3.2-7.5%) of those having standard assessment. In fetuses undergoing dedicated neurosonography, the rate of a CNS anomaly detected exclusively on MRI is lower than that reported previously. Early MRI has an excellent diagnostic performance in identifying additional CNS anomalies, although the findings from this review suggest that MRI performed in the third trimester may be associated with a better detection rate for some types of anomaly, such as cortical, white matter and intracranial hemorrhagic anomalies. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.
Highlights
(VM) encompasses a spectrum of conditions characterized by dilatation of the lateral ventricles of the brain, typically defined as > 10 mm at the level of the atria, with or without dilatation of the third or fourth ventricle[1,2,3,4]
When stratifying the analysis according to the type of ultrasound assessment, the rate of associated anomalies detected only on magnetic resonance imaging (MRI) was 5.0% when dedicated neurosonography was performed compared with 16.8% in cases that underwent a standard assessment of the fetal brain in the axial plane
The risk of detecting an associated central nervous system (CNS) abnormality on MRI was higher in fetuses with moderate than in those with mild VM (odds ratio, 8.1; P = 0.001), while
Summary
(VM) encompasses a spectrum of conditions characterized by dilatation of the lateral ventricles of the brain, typically defined as > 10 mm at the level of the atria, with or without dilatation of the third or fourth ventricle[1,2,3,4]. VM is the most common prenatally diagnosed fetal brain anomaly, with a reported prevalence ranging from 1:1600 to 1:50 newborns[1,2,3,4]. VM is commonly categorized, according to the degree of ventricular dilatation, as mild (10–12 mm), moderate (13–15 mm) or severe (> 15 mm); the rationale for such classification relies on the fact that the risk of associated anomalies and abnormal neurodevelopmental outcome is higher with increasing degree of dilatation[5]. The main determinants of postnatal outcome in fetuses presenting with VM are the etiology, presence of associated anomalies and severity of ventricular dilatation. The main issues to be resolved during the diagnostic work-up of a fetus with VM are ruling out infection and chromosomal, central nervous system (CNS) and non-CNS anomalies[7]
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