MRI of a 6-year-old child shows a posterior fossa cyst communicating with the fourth ventricle, enlarged posterior fossa, and hypoplasia/agenesis of the cerebellar vermis. What is the diagnosis?

• A Mega cisterna magna
• B Blake's pouch cyst
• C Arachnoid cyst of the posterior fossa
• D Dandy-Walker malformation ✓

Explanation

Dandy-Walker malformation (DWM) is defined by the triad: (1) cystic dilatation of the fourth ventricle communicating with a posterior fossa cyst, (2) hypoplasia or agenesis of the cerebellar vermis (partial/complete), and (3) enlarged posterior fossa with upward displacement of the tentorium and torcular-lambdoid inversion. Mega cisterna magna has a normal vermis and does not communicate with the fourth ventricle. Blake's pouch cyst (persistent Blake's pouch) shows an infravermian cyst communicating with the fourth ventricle but the vermis is intact and rotated upward. Arachnoid cyst does not communicate with the fourth ventricle.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.