"Lemon sign" & "Banana sign" on Antenatal USG is seen in:

Chiari malformations: Chiari malformation I: most common peg-like cerebellar tonsils displaced into the upper cervical canal through the foramen magnum Chairi malformation 1.5: described in the literature as both a condition in its own right as well as a variant of Chiari I malformation caudal descent of cerebellar tonsils and brain stem Chiari malformation 2: displacement of the medulla, fouh ventricle and cerebellar vermis through the foramen magnum usually associated with a lumbosacral spinal myelomeningocele. Chiari malformation 3: features similar to Chiari II, but with an occipital and/or high cervical encephalocele. Chiari malformation 4: severe cerebellar hypoplasia without displacement of the cerebellum through the foramen magnum probably a variation of cerebellar hypoplasia Chiari V malformation: absent cerebellum herniation of the occipital lobe through the foramen magnum Chiari 0 malformation: syrinx without cerebellar tonsillar, or brain stem descent infrequently used and confusing term to be avoided based on repos of syrinx improvement after posterior fossa decompression LEMON SIGN: anterior bowing of frontal bone BANANA SIGN: wrapping of cerebellum around brainstem 100 % of lumbar malignancies have Chiari malformation Dandy-Walker malformation: - agenesis of cerebellar vermis - large posterior fossa