At 20-week anomaly scan, the fetus has a lemon-shaped skull, banana-shaped cerebellum (obliterated cisterna magna), and bilateral ventriculomegaly. The spine shows a posterior defect at L4 level. The most likely diagnosis and associated open neural tube defect are:

• A Dandy-Walker malformation with cervical meningocele
• B Holoprosencephaly with anterior encephalocele
• C Agenesis of corpus callosum with spina bifida occulta
• D Chiari II malformation with open myelomeningocele ✓

Explanation

The lemon sign (frontal bossing) and banana sign (Chiari II downward herniation of cerebellum, obliterating the cisterna magna) are the classic ultrasound markers of Chiari II malformation, which virtually always accompanies open lumbosacral myelomeningocele. Ventriculomegaly results from obstructive hydrocephalus. Dandy-Walker shows enlarged posterior fossa, not obliterated cisterna magna. Holoprosencephaly shows fused cerebral hemispheres.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.