Conjoined twins

A monoamniotic twin gestation in which the twins share one or more organs.

Infans bicorporeus xyphopagus

Kind met twee hoofden, RP-P-OB-10.106

Conjoined twins are also known as siamese twins, and are a rare phenomenon in which two individuals are born physically connected to each other. This condition results from a monoamniotic twin gestation, where the twins share the same amniotic sac during development and can share one or more organs.

Development and Causes

Monoamniotic twins develop from a single fertilized egg, or zygote, that fails to separate completely after around 8 to 12 days following fertilization. If the separation occurs later than this, the twins can become conjoined. The exact cause of the incomplete separation is unknown.

Types of Conjoined Twins

There are several types of conjoined twins, categorized based on the point of attachment:

• Thoracopagus: Attached at the upper portion of the torso, sharing a heart.
• Omphalopagus: Attached at the lower chest and upper abdomen, may share liver but usually have separate hearts.
• Pygopagus: Attached back to back at the buttocks, may share a lower gastrointestinal tract.
• Craniopagus: Attached at the head, the rarest type.

Diagnosis

Prenatal ultrasound is the primary method for diagnosing conjoined twins during pregnancy. More detailed imaging, like MRI or CT scan, may be used to understand the extent of organ sharing and plan for possible separation surgery.

Treatment and Prognosis

Treatment for conjoined twins varies greatly depending on the degree of organ sharing and overall health of the twins. If feasible, surgical separation may be considered, but carries significant risks. The prognosis for conjoined twins varies widely, with survival rates higher for those who share fewer organs.

See Also

• Monozygotic twins
• Twin
• Prenatal Diagnosis

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