Introduction: Ventricular dilatation is generally defined on ultrasounds (US) or MRI as an atrium larger than 10 to 12 mm on axial or coronal planes. After 22 weeks, this measure is independent of the term.
Methods: In the view of the prognostication, it is of utmost importance to not only calculate the width of the ventricles but also to estimate the progression of the ventriculomegaly, and to look for associated structural or genetic anomalies. In this respect, it is essential to study the shape, thickness, echogenicity or signal (on MRI) of the ependymal lining, to appreciate the echoic or radiological characteristics of the ventricular content, to search for brain malformations, to calculate the biparietal diameter, head circumference and width of the subarachnoid spaces, to know the karyotype and to search for fetal infection or extracranial malformation. Complete US evaluation, MRI, and amniocentesis must therefore be part of the routine check-up of these fetuses.
Discussion: The prognosis is still debated. It is usually considered to be poor in cases of associated malformations or brain insult, tri- or tetraventricular enlargement and karyotype anomalies. On the contrary, it is generally considered as good when ventriculomegalies are isolated, biventricular, stable, slowly evolving or regressive.
Conclusion: The relationship between the size of the ventricles and the uni- or bilateral character of the dilatation are still a matter of debate.