A 20-week antenatal ultrasound shows a fetus with ventriculomegaly (atrial width 14 mm), absent corpus callosum, and small posterior fossa. The cisterna magna is not visualised. These findings are MOST consistent with:
- A Dandy-Walker malformation
- B Chiari II malformation (Arnold-Chiari) ✓
- C Holoprosencephaly
- D Agenesis of corpus callosum as an isolated finding
Explanation
Chiari II malformation is associated with lumbar myelomeningocele and is characterised on fetal ultrasound by the 'lemon sign' (frontal bossing — scalloping of frontal bones), 'banana sign' (curved cerebellum — herniation of cerebellum through foramen magnum obliterating the cisterna magna), small posterior fossa, ventriculomegaly, and absence of the cisterna magna. Absent corpus callosum can co-exist. Dandy-Walker shows an enlarged posterior fossa with cystic dilation of the 4th ventricle. Holoprosencephaly shows absent interhemispheric fissure. Isolated ACC would not obliterate the cisterna magna.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.