Evaluation of the lemon and banana signs in one hundred thirty fetuses with open spina bifida.

The incidence and diagnostic accuracy of the lemon and cerebellar ultrasonographic markers, as well as head size and ventriculomegaly, were evaluated in a study of 1561 patients at high risk for fetal neural tube defects. In the 130 fetuses with open spina bifida there was a relationship between gestational age and the presence of each of these markers. The lemon sign was present in 98% of fetuses at less than or equal to 24 weeks' gestation but in only 13% of those at greater than 24 weeks' gestation. Cerebellar abnormalities were present in 95% of fetuses irrespective of gestation; however, the cerebellar abnormality at less than or equal to 24 weeks' gestation was predominantly the banana sign (72%) whereas at gestations greater than 24 weeks it was cerebellar "absence" (81%). Both growth retardation and cerebral ventriculomegaly significantly worsened with gestation while the head circumference remained disproportionately small throughout gestation. On the basis of these data, a new approach is proposed for the investigation of patients at high risk for fetal open spina bifida.