Which sign is associated with neural tube defects such as open spina bifida?

• A. Lemon sign
• B. Keyhole sign
• C. Hypotelorism
• D. Macroglossia

Answer: (A)

Lemon sign is a fetal skull contour finding seen on ultrasound in cases of open spina bifida. The frontal bones appear scalloped and the head takes on a lemon-like shape due to changes in intracranial pressure from associated hindbrain herniation (Arnold-Chiari II malformation). This feature is typically seen in the second trimester and is a classic clue pointing to a neural tube defect like open spina bifida. The other signs describe different conditions: the keyhole sign indicates posterior urethral valves, hypotelorism is a reduced distance between the eyes seen with holoprosencephaly, and macroglossia is an enlarged tongue seen in Beckwith-Wiedemann syndrome.