Role of prenatal magnetic resonance imaging in fetuses with isolated mild or moderate ventriculomegaly in the era of neurosonography: a multicenter study

OBJECTIVES: To assess the role of fetal magnetic resonance imaging (MRI) in detecting associated anomalies in fetuses presenting with mild and moderate isolated ventriculomegaly (VM) undergoing multiplanar ultrasound (US) evaluation of fetal brain. METHODS: Multicenter, retrospective, cohort study involving 15 referral fetal medicine centers in Italy, United Kingdom, and Spain. Inclusion criteria were fetuses affected by isolated VM on US, defined as VM with normal karyotype and no other additional central nervous system (CNS) and extra-CNS anomalies on US, undergoing detailed assessment of fetal brain via a multiplanar approach as suggested by ISUOG guidelines on fetal neurosonogram. The primary outcome of the study was to report the rate of additional CNS anomalies detected exclusively at prenatal MRI and missed at US, while the secondary aim was to estimate the incidence of additional anomalies detected exclusively after birth and missed at prenatal imaging (US and MRI). Sub-group analyses according to the gestational age at MRI (< vs ≥ 24 weeks of gestation), laterality of VM (unilateral vs bilateral), and severity of dilatation (mild vs moderate VM) were also performed. RESULTS: Five-hundreds and fifty-six fetuses with a prenatal diagnosis of isolated fetal VM on US were included in the analysis. Additional structural anomalies were detected at prenatal MRI and missed at US in 5.4% (95% CI 3.8-7.6) of cases. When considering the type of anomalies, supra-tentorial intra-cranial hemorrhage was detected on MRI in 26.7% of fetuses, while polymicrogyria and lissencephaly in 20.0% and 13.3% of cases, respectively. Hypoplasia of the corpus callosum was detected at MRI in 6.7% of cases, while dysgenesis in 3.3%. Fetuses with an associated anomaly detected only at MRI were more likely to have moderate compared to mild VM (60.0% vs 17.7%, p<0.001), while there was no significant difference between the proportion of cases with bilateral VM between the two groups (p=