MRI of a 6-month-old with hydrocephalus shows complete agenesis of the cerebellar vermis, a large midline posterior fossa cyst continuous with the fourth ventricle, and elevation of the tentorium and torcula. What is the diagnosis?

• A Arnold-Chiari malformation type II
• B Vein of Galen malformation
• C Aqueductal stenosis
• D Dandy-Walker malformation ✓

Explanation

The Dandy-Walker triad consists of vermian agenesis or hypoplasia, a cystic dilatation of the fourth ventricle filling an enlarged posterior fossa, and upward displacement of the tentorium and torcula (torcular-lambdoid inversion). Arnold-Chiari II features downward hindbrain herniation through the foramen magnum, typically with myelomeningocele and a small posterior fossa. Aqueductal stenosis spares the posterior fossa structures, and vein of Galen malformation shows a vascular nidus with high-flow flow voids.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.