Fetal magnetic resonance imaging of the brain: is ventriculomegaly the tip of the syndromal iceberg?

Ventriculomegaly discovered on prenatal ultrasound examinations is frequently a significant challenge both for the accurate identification of the etiology of ventriculomegaly as well as for adequate parental counseling. Fetal ventriculomegaly is usually easily depicted on prenatal ultrasound studies. It is, however, of utmost importance to differentiate between the various forms of ventriculomegaly. A ventriculomegaly may be "isolated" or part of a syndrome. In addition, ventriculomegaly may be a complication of an intrauterine infection or hemorrhage. A correct differentiation between the various etiologies of ventriculomegaly is essential to predict outcome and to guide the various treatment options which may start as early as in the fetal time period. Prenatal ultrasound may be limited in the correct identification of subtle "additional" lesions that would point to the "overall" diagnosis. The high spatial resolution and various anatomical and functional image contrasts that can be generated by prenatal magnetic resonance imaging (MRI) have proven to be especially beneficial for complex fetal brain pathologies. In addition, prenatal MRI allows study of the entire fetus including the spinal cord and canal. In the current manuscript the various fetal MRI techniques are being discussed. In addition, the various causes of isolated, acquired and syndromal ventriculomegaly are presented as well as their imaging appearance on fetal MRI. Finally, a short summary on the various theories on ventriculomegaly versus hydrocephalus are presented.