Twin Peak Sign

The twin peak (or lambda) sign is a wedge of placental tissue that extends from the placental surface between the layers of the inter-twin membrane and indicates a dichorionic-diamniotic twin gestation. The inter-twin membrane in dichorionic-diamniotic twins is made up of sets of amniotic and chorionic layers from each fetus.

This sign is helpful when there is a single placenta, a dividing membrane and twins of the same gender. The diagnostic dilemma in this case is between a monozygotic gestation (monochorionic-diamniotic) and a dizygotic gestation with fused placentas (dichorionic-diamniotic) whose twins just happen to be the same gender. The twin peak sign will clinch the diagnosis for a dichorionic-diamniotic twin gestation.

References

Trop I. The twin peak sign. Radiology. 2001 Jul;220(1):68-9