A 32-year-old primigravida was referred to our centre at 18 weeks of gestation (WOG). The female fetus showed an isolated mild unilateral ventriculomegaly of 12mm in the atrium. Amniocentesis and TORCH showed inconspicuous results. In 26 WOG a magnetic resonance imaging (MRI) was carried out with an 1,5 Tesla system. The MRI confirmed the ventriculomegaly and described nodules of variable size protruding into the ventricular lumen and additionally a square shape of the frontal horns of the lateral ventricles. These changes are typical for a periventricular nodular heterotopia (PNH). Analysis of ultrasound images two days after MRI showed in the axial plane hyperechoic irregularities of the lateral borders of the lateral ventricles, which corresponded, to the nodules in the MRI. The coronal ultrasound views confirmed the square shaped frontal horns described in the MRI. Additional MRI of the mother gave no indication of PNH. Mutations in the FLNA gene are associated with the most common phenotype of PNH, but in our case it was negative without proof of mutations. The majority of patients with PNH suffer from epilepsy, seizures and/or developmental delay. In summary, in routine prenatal ultrasound PNH is underdiagnosed but irregular ventricular border with noduls protruding into the ventricular lumen in the axial plane and square shaped frontal horns in the coronal plane can point to PNH. MRI can confirm the ultrasound suspicion. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.