Conjoined Twins

Conjoined Twins
Anne Kennedy, MD
DIFFERENTIAL DIAGNOSIS
Common
  • Thoracopagus
  • Omphalopagus
Less Common
  • Pygopagus
  • Ischiopagus
  • Cephalopagus
  • Craniopagus
Rare but Important
  • Dicephalus
  • Fetus-in-Fetu
  • Parasitic Twin
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
  • Monochorionic
    • Single placenta
    • Twins same gender
  • Monoamniotic
    • No inter-twin membrane
  • Fetuses fused at some location
    • Contiguous skin covering at site of fusion is hallmark of this diagnosis
    • Conjoined twins with narrow or pliable area of fusion may vary in orientation to each other
  • May see fused umbilical cord
    • More than three cord vessels
  • Important to differentiate conjoined from monoamniotic twins given different prognosis
    • Monoamniotic twins are within the same sac but not fused
    • May have relatively fixed orientation if cord entanglement
    • Prognosis better for monoamniotic
      • No need for separation
      • Majority of conjoined twins die in utero or shortly after delivery
  • Formal fetal echocardiography mandatory in all conjoined twins
    • Complex congenital heart disease may preclude separation attempt
    • Fetal echocardiography easier than postnatal echo
      • Multiple acoustic windows through amniotic fluid
      • No interference from aerated lung
Helpful Clues for Common Diagnoses
  • Thoracopagus
    • Fetuses face each other
    • Fused from thoraces to umbilicus
    • Always some degree of cardiac fusion
      • Precludes separation in 75%
    • Common pericardial sac in 90%
    • Livers invariably fused
      • 25% share biliary system
    • 25% have common small intestine, usually duodenum
  • Omphalopagus
    • Fetuses face each other
    • Fusion of ventral abdominal cavities from umbilicus ± lower thorax
    • 80% liver fusion, biliary anomalies common
    • 30% have shared small intestine at distal ileum at level of Meckel’s diverticulum
Helpful Clues for Less Common Diagnoses
  • Pygopagus
    • Fetuses face away from each other
    • Joined at sacrum/buttocks
    • 15% share urinary system with single bladder
    • One anus ± rectum, rest of bowel separate
    • May have spinal cord fusion
  • Ischiopagus
    • Joined from umbilicus to single pelvis
    • Fetuses face-to-face or end-to-end
    • Variable number kidneys/bladder
    • Cloacal malformation/anal atresia/vesicocolic fistulas occur
    • Internal and external genitalia may be shared
    • Variable number of extremities
      • Tetrapus = 4
      • Tripus = 3
      • Bipus = 2
    • Major challenges to separation are genitourinary and orthopedic
    • Genitourinary
      • Continence, adequate bladder/bowel emptying/sexual function
    • Orthopedic
      • Number of lower limbs
      • Pelvic reconstruction for prosthetic limb attachment
  • Cephalopagus
    • Joined from vertex to umbilicus with faces on opposite sides of common head
    • Inseparable
  • Craniopagus
    • Joined at skull anywhere except face or foramen magnum
    • Separability depends on degree of shared dural sinuses
    • Shared neural tissue precludes separation
Helpful Clues for Rare Diagnoses
  • Dicephalus
    • Two heads
    • Single torso
    • Usually single set of extremities
    • Inseparable
  • Fetus-in-Fetu
    • “Twin” forms a mass within an apparent singleton
    • Key difference between teratoma and fetus-in-fetu is presence of vertebral column
    • Mass is well-demarcated as contained within a membranous sac
    • Commonest in upper retroperitoneum
    • No malignant potential
    • Excision is curative
  • Parasitic Twin
    • Vestigial fetal parts or incomplete twin attached to fully developed co-twin
      • Intact twin known as autosite
      • Any vestigial parts may be seen
Other Essential Information
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Aug 10, 2016 | Posted by in OBSTETRICS | Comments Off on Conjoined Twins

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