Which imaging sign is commonly associated with Arnold-Chiari II malformation and describes a banana-shaped cerebellum?

Which imaging sign is commonly associated with Arnold-Chiari II malformation and describes a banana-shaped cerebellum?

• A. Banana sign
• B. Moon sign
• C. Clover sign
• D. Psi sign

Answer: (A)

Downward displacement of the hindbrain in Arnold-Chiari II causes the cerebellar vermis and tonsils to herniate through the foramen magnum, crowding the posterior fossa. On ultrasound this alters the cerebellum’s shape into a curved, elongated form that resembles a banana—the banana sign. This distinctive appearance is a hallmark of Chiari II and is frequently seen when spina bifida (often myelomeningocele) is present. The other signs describe different cranial or posterior fossa findings and do not depict the curved cerebellum, so they don’t fit the imaging appearance described.

Downward displacement of the hindbrain in Arnold-Chiari II causes the cerebellar vermis and tonsils to herniate through the foramen magnum, crowding the posterior fossa. On ultrasound this alters the cerebellum’s shape into a curved, elongated form that resembles a banana—the banana sign. This distinctive appearance is a hallmark of Chiari II and is frequently seen when spina bifida (often myelomeningocele) is present. The other signs describe different cranial or posterior fossa findings and do not depict the curved cerebellum, so they don’t fit the imaging appearance described.