Posterior fossa cyst on prenatal ultrasonography. (Figure 1) Figure 1. Postnatal sagittal T1-weighted and contrast enhanced axial T1-weighted images demonstrate intact cerebellar vermis and retrocerebellar cerebrospinal fluid containing cystic structure with dura folds (arrows). ### Prenatal and Birth Histories The caesarian section delivery at 35 weeks of gestation had no complications. ### Physical Examination Routine laboratory results were within normal limits. Urine cytomegalovirus culture result was negative. Feeding, voiding, and stooling were progressing uneventfully. A postnatal head ultrasonogram confirmed the earlier finding of a posterior fossa cyst. The infant and her mother were transferred to the level 3 neonatology unit of the hospital for further evaluation and precise diagnosis. Brain magnetic resonance imaging (MRI) revealed an intact cerebellar vermis and a retrocerebellar cerebrospinal fluid–containing cystic structure that demonstrated dura folds. There …