Role of magnetic resonance imaging in fetuses with mild or moderate ventriculomegaly in the era of fetal neurosonography: systematic review and meta-analysis

To report the rate of additional anomalies detected exclusively on prenatal MRI in fetuses affected by isolated mild or moderate ventriculomegaly (VM) according to the type of ultrasound protocol adopted (dedicated neurosonography vs standard assessment of fetal brain) and to explore whether the diagnostic performance of fetal MRI in detecting such anomalies is affected by gestational age at scan and laterality of ventricular dilatation. The primary aim was to report the rate of additional anomalies detected exclusively on prenatal MRI in fetuses affected by isolated mild and moderate VM (ventricular dilatation between 10-15 mm) undergoing compared to those not undergoing dedicated neurosonography, defined as a detail assessment of fetal brain according to the International Society of Ultrasound in Obstetrics and Gynecology guidelines. Medline, Embase, Cinahl and Clinicaltrials.gov databases were searched. Additional anomalies were classified in: callosal, septal, posterior fossa, white matter, intra-ventricular hemorrhage, cortical, peri-ventricular heterotopia, peri-ventricular cysts and complex malformations. Furthermore, we calculated the rate of additional CNS anomalies missed at prenatal MRI and detected only at birth in fetuses who had early (≤24 weeks) compared to late (>24 weeks of gestation) MRI. A sub-analysis was performed according to the laterality (uni- vs bi-lateral VM) and the degree (mild vs moderate, defined as ventricular dilatation between 10-12 and 13-15 mm respectively) of ventricular dilatation. Finally, we explore whether MRI assessment led to a significant change in the prenatal management. Random-effect meta-analyses of proportions were used to analyze the data. 16 studies (1159 fetuses) were included in the systematic review. Overall, fetal MRI detected 10.0% (95% CI 6.2-14.5; 92/1159) of fetal anomalies not detected on ultrasound. However, when stratifying the analysis according to the type of ultrasound assessment performed, the rate of associated anomalies detected only on MRI was 5.0% (95% CI 3.0-7.0; 28/596) when dedicated neurosonography was undertaken compared to 16.8% (95% CI 8.3-27.6; 64/563) of anomalies detected in cases undergoing a standard assessment of fetal brain though the axial plane. The overall rate of additional anomalies detected only at birth and missed at prenatal MRI was 0.9% (95% CI 0.04-1.5, I2 : 0%; 8/1159). There was no difference in the rate of associated anomalies detected only after birth when fetal MRI was carried out before compared to after 24 weeks of gestation (p=0.265). The risk of detecting associated CNS abnormalities on MRI was higher for fetuses with moderate compared to mild VM (OR: 8.1, 95% CI 2.3-29.0, p= 0.001), while there was no difference for those presenting with bilateral compared to unilateral ( p= 0.333) dilatation. Finally, a significant change in perinatal management, mainly TOP for parental request, following MRI detection of associated anomalies was observed in 2.9% (95% CI 0.01-1.0) of fetuses undergoing neurosonography compared to 5.1% (95% CI 3.2-7.5) of those having standard assessment. In fetuses undergoing dedicated neurosonography, the rate of CNS anomalies detected exclusively on MRI is lower compared to what has been previously reported. 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 anomalies, such as cortical, white matter and intracranial hemorrhage.