Chiari II malformation involves downward displacement of which brain structure?

Chiari II malformation involves downward displacement of which brain structure?

• A. Posterior cerebellum
• B. Frontal lobe
• C. Occipital lobe
• D. Basal ganglia

Answer: (A)

Chiari II malformation is a hindbrain herniation pattern seen with neural tube defects like myelomeningocele. In this condition, parts of the hindbrain descend through the foramen magnum into the upper cervical canal. The structure that mainly moves downward is the posterior portion of the brain—the cerebellum (often the cerebellar vermis) and adjoining brainstem. This is why the posterior cerebellum is the correct choice. The other structures listed reside in the cerebral hemispheres and do not undergo this downward displacement in Chiari II, so they don’t account for the malformation.