Lemon sign is seen in :

Spina bifida is a defect in the neural arch,which results in exposure of the contents of the neural canal. Most of them are seen in lumbosacral region.They may be open and closed. Banana sign: Compression or flattening of the posterior cerebellar surface. Lemon sign: Concave deformity of the frontal bones. Both above banana sign and lemon sign seen in USG in open spina bifida. Anencephaly: Absence of calvarium. Spina bifida occulta: Veebral schisis covered by normal soft tissue. Spina bifida apea: Full thickness defect of the skin and veebral arches. Cystic hygroma: Fluid filled sac that results from the obstruction of Lymphatic system. Commonly located in the neck or head area but can be present anywhere in the body. Tear drop sign: Absence of Corpus callosum. Reference: DC Duttas Textbook of Obs, 9th edition,page no.602.