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






Image Gallery