Abstract
Medulloblastoma is one of the common posterior fossa tumors in children. The natural history of this tumor in presymptomatic period is not well known. Widespread use of brain imaging has increased the detection of incidental brain tumors in totally asymptomatic persons. Here, we report a case of a 4-year-old boy with prenatal diagnosis of congenital brain abnormalities and neurofibromatosis type I. He underwent regular brain imaging to follow interhemispheric arachnoid cyst and ventriculomegaly that a posterior fossa tumor was discovered. The tumor size increased during time and became symptomatic after 28 months which was resected.