Neural tube defect in monochorionic diamniotic twin pregnancy

Case contributed by Alexandra Stanislavsky
Diagnosis certain


Second trimester morphology ultrasound

Patient Data

Age: 30 years
Gender: Female

Gestation: 18w1d, MCDA pregnancy.

TWIN 1 (maternal right, cephalic presentation): Biometry normal for gestational age. Normal fetal anatomy. DVP: 4.8 cm

 TWIN 2 (left side breech presentation): Biometry normal for gestational age.
The following abnormalities are demonstrated:

  • Mild ventriculomegaly with lateral ventricles measuring 11 mm on both sides. CSP and corpus callosum not identified, possibly due to the early gestation and ventriculomegaly.
  • The cerebellum is displaced posteriorly consistent with Chiari type 2 malformation. 
  • There is a neural tube defect extending from L4/L5 down through the sacral spine. The conus appears to extend into the defect. 
  • Bilateral talipes

Deepest pool: 3.8 cm

Placenta: Posterior, not low lying. Twin 1 centric cord insertion; twin 2 velamentous cord insertion. The cervix is long and closed.

Case Discussion

MCDA pregnancy with twin 2 demonstrating typical antenatal features of a neural tube defect - including a lemon-shaped head, posteriorly displaced "banana" cerebellum, ventriculomegaly and a lumbar myelomeningocele.

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