A posterior fossa MRI shows a midline T1 hypointense T2 hyperintense cyst communicating with the fourth ventricle, with complete vermian agenesis and a large posterior fossa with elevation of the torcular herophili. What is the diagnosis?
- A Dandy-Walker malformation ✓
- B Mega cisterna magna
- C Blake's pouch cyst
- D Joubert syndrome
Explanation
Dandy-Walker malformation is characterised by the triad: (1) complete or partial agenesis of the cerebellar vermis, (2) cystic dilation of the fourth ventricle that fills the posterior fossa, and (3) enlargement of the posterior fossa with elevation of the torcular herophili (lambda above asterion). Communication of the cyst with the fourth ventricle differentiates it from arachnoid cyst. Mega cisterna magna has normal vermis and fourth ventricle. Blake's pouch cyst has normal vermis with cyst posterior to normal-looking cerebellum. Joubert syndrome shows the molar tooth sign on axial MRI (superior cerebellar peduncle thickening).
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.