Prenatal diagnosis by 3D ultrasound and MRI of an unusual malformation of cortical development with brain-in-brain appearance.

A 31-year-old pregnant woman was referred for isolated mild ventriculomegaly and failure to visualize the left lateral ventricle's anterior horn on second trimester sonography (US). Three-dimensional US suspected a frontal lesion deviating the midline. MRI revealed a mass compressing the ventricle.