A two day old baby boy was sent for ultrasonography of the skull as a part of routine screening.
Transfontanelle ultrasonography reveals a large anechoic cystic structure in the posterior fossa. The cerebellar hemispheres are absent. The CT scan shows dilatation of both lateral ventricles and the third and fourth ventricles. The posterior fossa is expanded with a large cyst communicating with the fourth ventricle. The cerebellar vermis is hypoplastic.