Asymmetric Fluid Distribution



Asymmetric Fluid Distribution


Anne Kennedy, MD



DIFFERENTIAL DIAGNOSIS


Common



  • Twin-Twin Transfusion Syndrome


  • Discordant Twin Growth


  • Unequal Placental Sharing


  • Oligohydramnios of One Twin


  • Polyhydramnios of One Twin


Less Common



  • Premature Rupture of Membranes


  • Myomatous Uterus


ESSENTIAL INFORMATION


Key Differential Diagnosis Issues



  • Asymmetric fluid distribution may be caused by primary abnormality in one twin or complication of placental sharing


  • Determination of chorionicity vital to management



    • Anomaly in one dichorionic twin



      • Management focused on maximizing outcome for normal fetus


      • Early intervention for anomalous twin confers additional risks of prematurity on normal twin


    • Monochorionic twins



      • Demise of one twin has potentially disastrous consequences for survivor


      • Intervention may be appropriate despite risks of prematurity


    • Twin-twin transfusion syndrome (TTTS) has high mortality for both twins if untreated


    • Twin reversed arterial perfusion (TRAP) sequence



      • Management is focused on maximizing outcome for pump twin


Helpful Clues for Common Diagnoses



  • Twin-Twin Transfusion Syndrome



    • Monochorionic placentation


    • Fetuses often discordant in size: Donor small/recipient large


    • Donor twin: Oligemic → ↓ urine production → “absent” bladder + oligohydramnios


    • Recipient twin: Plethoric, polyhydramnios, at risk for hydrops


  • Discordant Twin Growth



    • Smaller twin may be structurally abnormal ± aneuploid


    • Look for signs of growth restriction



      • Decreased abdominal circumference, estimated fetal weight < 10th percentile, oligohydramnios


    • Differentiate from normal but asymmetric twins



      • Serial evaluation shows appropriate interval growth with normal fluid volume around both


  • Unequal Placental Sharing



    • Best time to look at placental cord insertion site is late first trimester


    • Look for eccentric cord placement



      • Twin with smaller area of placenta at risk for growth restriction/oligohydramnios


    • Velamentous cord: Cord inserts onto membranes away from placental disc


    • Marginal cord: Cord inserts at edge of placental disc


  • Oligohydramnios of One Twin



    • Demise


    • Bilateral renal anomaly



      • Renal agenesis: Absent kidneys, absent renal arteries, “lying down” adrenals


      • Multicystic dysplastic kidneys: Variable sized cysts, no normal renal parenchyma


      • Severe UPJ obstruction: Dilated pelves/calyces without hydroureter


      • Obstructive cystic dysplasia: Multiple cysts within echogenic parenchyma ± residual hydroureter


    • Posterior urethral valves



      • Dilated bladder


      • “Keyhole” appearance due to dilated posterior urethra


      • Bilateral hydronephrosis


      • Look for urinoma/urinary ascites


    • Intrauterine growth restriction (IUGR)



      • Estimated fetal weight < 10th percentile


      • Decreased abdominal circumference


      • Use spectral Doppler to assess uteroplacental circulation/fetal response to adverse environment


  • Polyhydramnios of One Twin



    • Idiopathic


    • Gastrointestinal obstruction



      • Look for dilated loops of bowel or “double bubble” sign


      • May not become apparent until 3rd trimester


    • CNS impairment → inability to swallow



    • Obstructed swallowing: Goiter, oral mass, neck mass



      • Scan head and neck in axial plane


      • Look for splaying of carotid arteries with goiter


    • High output state



      • Arteriovenous malformation: Use color Doppler to assess any apparent “cystic” structure


      • Tumor: Most fetal tumors are large/rapidly growing, use color Doppler to assess internal vascularity


      • Chorioangioma: Hypervascular placental mass


    • Musculoskeletal anomaly



      • Skeletal dysplasia: Assess bone mineralization, measure all long bones


      • Arthrogryposis/akinesia sequence: Evaluate movement/swallowing in real time


Helpful Clues for Less Common Diagnoses

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Aug 10, 2016 | Posted by in OBSTETRICS | Comments Off on Asymmetric Fluid Distribution

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