Conjoined Twins

KEY FACTS

Terminology

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Fetal fusion of variable degree
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Nomenclature
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  Site of fusion + suffix “pagus”
  - –
    
    Omphalopagus : Abdomen fused from xiphoid to umbilicus, heart not involved
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  Prefix “di” denotes separate parts associated with conglomerate structure
  - –
    
    Dicephalus : Conglomerate mass with 2 identifiable heads

Imaging

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Only occurs with monochorionic twinning
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  Single placental mass
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  No intertwin membrane
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  Fetuses inseparable, but relative position is not always constant
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  Often hyperextension of cervical spines, unusual limb positioning
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Fused umbilical cords common
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Polyhydramnios in 50%

Scanning Tips

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Look for contiguous skin covering between fetuses for diagnosis of conjoined twins
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  Variable presentation does not exclude diagnosis
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  Connection may be extensive (e.g., thoracoomphalopagus) or quite small (e.g., ischiopagus)
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Use 3D US surface-rendered images to help parents understand anatomy
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Perform dedicated fetal echocardiography
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  High incidence of congenital heart disease
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  Acoustic access is better in utero than post delivery; fetuses stable on placental support
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Use color Doppler to assess shared organ blood supply
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  Omphalopagus twins: 80% share liver
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  Thoracopagus twins: 90% share pericardium, 75% share heart

Coronal oblique US shows 2 heads

and necks

on a single torso (i.e., dicephalus twins). As is so often the case, there are multiple anomalies, in this instance, bladder outlet obstruction

. This patient chose to terminate the pregnancy.

3D surface-rendered US demonstrates skin continuity

across the abdomens of these omphalopagus twins. Monoamniotic twins may be very close to each other and appear to be hugging, but they will not have contiguous skin covering.