MRI study revealed vermian agenesis which resulted in two cerebellar hemispheres in contact at the midline. Axial T1 and T2 images showed dysplasia of the superior cerebellar peduncles that resulted in a molar tooth configuration. The more caudal T2-weighted transverse MR image showed the fourth ventricle shaped like opened bat wing. Furthermore, severe hypoplasia involving the inferior vermis resulted in an open communication between the fourth ventricle and the extracerebellar subarachnoid space but without evidence of a posterior fossa cyst. Size of the posterior fossa appears normal.