What do the lemon and banana signs on ultrasound suggest?

The lemon and banana signs observed on ultrasound are associated with specific neural tube defects, particularly Chiari malformation and spina bifida. The lemon sign refers to a characteristic shape of the fetal skull that appears irregular and flattened, indicative of cerebral tissue loss associated with conditions like spina bifida. Meanwhile, the banana sign indicates the shape of the cerebellum, which becomes elongated and curved, often seen in cases of Chiari malformation. These two ultrasound findings together strongly suggest the presence of these abnormalities.

While other choices mention different conditions, they do not correlate with the lemon and banana signs. For instance, spina bifida's inclusion in the correct answer reflects its direct relationship to the lemon sign, while Chiari malformation explains the banana sign. The other options like congenital heart defects, microcephaly, or holoprosencephaly do not exhibit these specific ultrasound findings, making them less relevant in this context. Hence, the response focusing on Chiari malformation and spina bifida is the accurate choice regarding the implications of those ultrasound signs.