Cisterna magna enlargement beyond 1.0 cm with ventriculomegaly and cerebellar hemispheric crowding is most consistent with which condition?

Cisterna magna enlargement beyond 1.0 cm with ventriculomegaly and cerebellar hemispheric crowding is most consistent with which condition?

• A. Dandy-Walker malformation
• B. Acrania
• C. Hydranencephaly
• D. Arachnoid cyst

Answer: (A)

This pattern points to a posterior fossa malformation where the cerebellar vermis is underdeveloped and the fourth ventricle dilates, creating a cystic enlargement of the posterior fossa. The enlarged cisterna magna (>1.0 cm) with ventriculomegaly and crowding of the cerebellar hemispheres is classic for Dandy-Walker malformation, which features vermian hypoplasia or agenesis, a dilated fourth ventricle, and posterior fossa enlargement that can extend to hydrocephalus. Acrania would show absence of the calvarium, hydranencephaly involves near-total loss of cerebral hemispheres, and an arachnoid cyst is a discrete cystic lesion that does not produce the same vermian hypoplasia and fourth-ventricle dilation pattern.

This pattern points to a posterior fossa malformation where the cerebellar vermis is underdeveloped and the fourth ventricle dilates, creating a cystic enlargement of the posterior fossa. The enlarged cisterna magna (>1.0 cm) with ventriculomegaly and crowding of the cerebellar hemispheres is classic for Dandy-Walker malformation, which features vermian hypoplasia or agenesis, a dilated fourth ventricle, and posterior fossa enlargement that can extend to hydrocephalus. Acrania would show absence of the calvarium, hydranencephaly involves near-total loss of cerebral hemispheres, and an arachnoid cyst is a discrete cystic lesion that does not produce the same vermian hypoplasia and fourth-ventricle dilation pattern.