Crescent-shaped cerebellum displayed with a coexisting neural tube defect is known as which sign?

• A. Banana Sign
• B. Frontal Bossing
• C. Corpus Callosum
• D. Hydrocephalus

Answer: (A)

The main idea here is recognizing a distinctive fetal brain sign that points to hindbrain herniation associated with open neural tube defects. When the cerebellum appears curved and disproportionately shaped in the sagittal view, taking on a crescent or banana-like contour, this is the banana sign. It reflects downward displacement of the hindbrain structures into the foramen magnum, a hallmark of Arnold-Chiari II malformation that commonly accompanies conditions like myelomeningocele. This sign helps clinch the diagnosis on ultrasound because the cerebellar morphology is directly altered by the hindbrain herniation.

While hydrocephalus can accompany these cases, and frontal bossing or abnormalities of the corpus callosum describe other features or conditions, they do not describe the specific curved cerebellar contour that defines the banana sign.