Mega-cisterna magna

A rare, non-syndromic, posterior fossa malformation characterized by a cisterna magna that measures above 15 mm in length, 5 mm in height and 20 mm in width (or greater than 10 mm in fetuses) associated with a normal cerebellar vermis and absence of hydrocephalus. The majority of patients are asymptomatic; however, variable neurodevelopmental outcomes, including delayed speech and language development, motor development delay, visiospatial perception difficulties, and attention problems, has been observed in some patients.