A 28-week foetal ultrasound shows a posterior fossa cyst communicating freely with the fourth ventricle, absent vermis, and the tentorium cerebelli is elevated. This triad is diagnostic of:
- A Dandy-Walker malformation ✓
- B Mega cisterna magna
- C Blake's pouch cyst
- D Arachnoid cyst of the posterior fossa
Correct answer: A. Dandy-Walker malformation
Explanation
The Dandy-Walker malformation triad comprises: (1) complete or partial agenesis of the cerebellar vermis, (2) cystic dilatation of the fourth ventricle communicating with a posterior fossa cyst, and (3) elevation of the tentorium cerebelli (high torcula). Mega cisterna magna has a normal vermis and normal fourth ventricle with a large cisterna magna. Blake's pouch cyst shows an intact vermis. Posterior fossa arachnoid cysts do 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.