Banana sign on USG is seen in :
Compression or flattening of the posterior cerebellar surface making a crescentic appearance (banana sign) is seen in open spina bifida and Arnols Chairi's malformation. Reference: Dutta's Textbook of Obstetrics 7th edition page no 647
Arnold Chiari malformation
Holoprosencephaly
Dandy walker malformation
Anencephaly
Diagnosis in obstetrics