Banana and lemon sign is seen in which fetal anomalies :

Signs of Spina bifida on USG : Small biparietal diameter Ventriculomegaly Frontal bone scalloping or the so called Lemon sign. Elongation and downward displacement of the cerebellum, the so called Banana sign Effacement or obliteration of the cisterna Magna. Ref:Williams Obs 23e pg 354,355.