- Umbilical vein varix
- Timing of Cranial Markers in Open NTD
- Real world experience Open Neural tube defect and Brain Signs
- Real world experience First Trimester Megacystis – Management
- Real world experience Fetal Megacystis
- Abnormal facial profile
- Azygous Vein & ARSA
- Blakes Pouch Cyst
- Absent nasal bone (ANB)
- Choroid plexus cysts
- Chronic placental abruption
- Fetal Alcohol Syndrome
- Placenta-First Risk Stratification
Timing of Cranial Markers in Open NTD
11–13+6 Weeks (First Trimester)
Most Sensitive Early Markers
Intracranial translucency (IT) obliteration
• IT (future 4th ventricle) not visible
• Very early posterior fossa crowding sign
• Often earliest detectable change
Small posterior fossa
• Reduced brainstem–occipital bone distance
• Brainstem appears thickened relative to posterior fossa
Early Banana Configuration
• Cerebellum begins to curve anteriorly
• Cisterna magna small or absent
NO Lemon sign @ present.
NO Hydrocephalus @ present.
14–18 Weeks (Early Second Trimester)
This is the peak detection window for cranial markers.
Banana Sign
• Cerebellum curved around brainstem
• Cisterna magna obliterated
• Highly suggestive
Lemon Sign
• Frontal bone scalloping
• Very common before 24 weeks
• Seen in majority of open NTD cases in this period
Small or Effaced Cisterna Magna
• More specific than lemon sign
Hydrocephalus may begin but often mild at this stage.
18–24 Weeks
Hindbrain herniation persists
Ventricular obstruction progresses
Findings:
• Persistent banana sign
• Lemon sign may still be present
• Ventriculomegaly begins to develop
• Fourth ventricle compression
• Aqueductal obstruction
This is when obstructive hydrocephalus becomes more evident.
After 24 Weeks
Lemon sign often disappears
• Skull ossifies
• Increased intracranial pressure reverses frontal scalloping
Banana sign usually persists
• Posterior fossa anatomy remains abnormal
Hydrocephalus becomes dominant
• Progressive ventriculomegaly
• Enlarged lateral ventricles
• Dangling choroid sign appears
At this stage, ventriculomegaly may be the most obvious finding.
| GA | Posterior Fossa | Lemon Sign | Ventricles | Key Message |
|---|---|---|---|---|
| 11–13+6 | IT obliterated, early banana | Rare | Normal | Look carefully at IT |
| 14–18 | Classic banana | Common | Usually mild | Peak cranial marker window |
| 18–24 | Persistent banana | May persist | Increasing VM | Hydrocephalus emerging |
| >24 | Banana persists | Often resolves | Marked VM | VM may dominate picture |
It Follows A Pattern
Early phase → Intracranial hypotension dominant
Mid phase → Hindbrain descent established
Late phase → Obstructive hydrocephalus dominates
So the biology shifts from:
CSF leak → posterior fossa crowding → aqueductal obstruction → ventricular dilation.
First trimester screening must evaluate intracranial translucency.
Lemon sign is most useful before 24 weeks.
Absence of lemon sign after 24 weeks does NOT exclude NTD.
Progressive ventriculomegaly later in pregnancy may be secondary to missed open NTD.
Posterior fossa assessment is more specific than frontal bone shape.