label: Lemon sign
label_lc: lemon sign
description: "The lemon sign refers to the shape of the fetal skull at ultrasonography (US) when the frontal bones lose their normal convex contour and appear flattened or inwardly scalloped. This gives the skull a shape that is said to resemble a lemon.. The sign is seen on transverse sonograms of the fetal cranium obtained at the level of the ventricles."