Twin Related Anomalies

Twin Related Anomalies
Anne Kennedy, MD
DIFFERENTIAL DIAGNOSIS
Common
  • Fetal Demise
  • Twin-Twin Transfusion Syndrome
  • Conjoined Twins
  • Twin Reversed Arterial Perfusion
Rare but Important
  • Fetus-in-Fetu
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
  • Most important step in evaluation of multiple gestation is determination of chorionicity
    • Certain problems only occur in monochorionic gestation
      • Twin-twin transfusion syndrome (TTTS)
      • Twin reversed arterial perfusion (TRAP)
      • Conjoined twins
  • Assess fluid distribution
    • Show fluid on either side of inter-twin membrane
    • Measure maximum vertical pocket for each twin
    • If fluid is asymmetric, determine which side is abnormal
      • Decreased in one twin: Oligohydramnios differential
      • Increased in one twin: Polyhydramnios differential
      • Increased in one twin & decreased in the other: TTTS most likely diagnosis
Helpful Clues for Common Diagnoses
  • Fetal Demise
    • Not uncommon in early pregnancy
    • Cardiac activity should always be seen in an embryo > 5 mm in crown rump length
    • If early, sac may completely resorb → “disappearing twin”
    • If later in monochorionic gestation, TRAP sequence may develop
    • Cord entanglement is a specific cause of demise in monoamniotic twins
  • Twin-Twin Transfusion Syndrome
    • Monochorionic gestation
    • Asymmetric or discordant growth
    • Abnormal fluid distribution: One twin with oligohydramnios, one with polyhydramnios
      • Look for “stuck” twin with shrink-wrapped membrane in severe cases
    • TTTS staging
      • Stage 1: Donor bladder visible, normal Doppler
      • Stage 2: Donor bladder empty, normal Doppler
      • Stage 3: Donor bladder empty, abnormal Doppler
      • Stage 4: Hydrops in recipient
      • Stage 5: Demise of one or both
  • Conjoined Twins
    • Monoamniotic gestation = no inter-twin membrane
    • Must have contiguous skin covering between fetuses
    • Nomenclature
      • Site of attachment & “pagus” (e.g., cephalopagus)
      • “Di” & site of duplication (e.g., dicephalus)
  • Twin Reversed Arterial Perfusion
    • Monochorionic gestation with one normal “pump” twin and one anomalous twin
    • Anomalous twin
      • Absent cardiac activity or rudimentary heart
      • Often well-developed torso/lower extremities
      • Upper extremities/cranium poorly developed or absent
      • Marked skin edema ± effusions/ascites
    • Hallmark of this condition is umbilical artery flow toward the abnormal fetus rather than toward the placenta
Helpful Clues for Rare Diagnoses
  • Fetus-in-Fetu
    • Apparent singleton: “Twin” is incorporated into the “singleton” as a mass
    • Always think about this with an unusual fetal mass
    • If vertebral column present image fetus-in-fetu more likely than teratoma
Other Essential Information
  • Anomaly rate higher in twin than singleton pregnancies
  • Any anomaly/aneuploidy can occur regardless of chorionicity
  • Specific entities arise from vascular connections in monochorionic placentas
    • TTTS arises secondary to artery to vein shunt within monochorionic placenta
      • Donor twin shunts arterial blood into recipient twin’s venous circulation → donor oligemia → effective “hypotension”
      • ↓ Renal perfusion → ↓ urine output → oligohydramnios
      • ↓ Blood to placenta → ↓ return of oxygenated blood → chronic hypoxia → poor growth
      • Recipient twin receives all its own return from placenta & portion of co-twins → plethora/fluid overload
      • ↑ Volume status → ↑ cardiac output → eventual development of hydrops
    • TRAP sequence arises secondary to artery to artery shunt within monochorionic placenta
      • Pump twin deoxygenated blood → co-twin umbilical arteries → preferential perfusion of lower extremities → lack of upper body/cranial development
      • Blood enters fetus via UA not UV → lack of normal circulation through heart → abnormal cardiac development
Alternative Differential Approaches
  • Twin with hydrops
    • Anomalous twin in TRAP sequence: Massive skin edema/effusions common
    • Pump twin in TRAP sequence at risk for hydrops from cardiac compromise
    • Both twins in TTTS at risk for hydrops (greater in recipient due to volume overload)
    • May have hydrops from other causes unrelated to placental sharing
      • All cases need careful anatomic survey, infection work up ± chromosome evaluation
      • Perform formal fetal echocardiography for structure, function, rate and rhythm
  • Twin with encephalomalacia
    • Any destructive process may end in encephalomalacia regardless of chorionicity
    • May occur secondary to chronic hypoxia in donor twin in TTTS
    • Monochorionic twin demise places surviving twin at risk for ischemic injury described as “twin embolization syndrome”
      • Shared placental circulation → vascular communications between fetuses
      • Death of one twin → sudden drop in peripheral resistance for survivor → effectively severe hypotensive episode
      • Ischemic injury seen in brain/myocardium/kidneys
    • Sonographic findings
      • ↑ Echogenicity in periventricular white matter, loss of grey-white matter differentiation
      • Eventual cystic encephalomalacia, porencephaly, microcephaly
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