Abnormal Placental Location

Abnormal Placental Location
Roya Sohaey, MD
DIFFERENTIAL DIAGNOSIS
Common
  • Placenta Previa
  • Marginal Sinus Previa
  • Placenta Accreta Spectrum
Less Common
  • Succenturiate Lobe
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
  • Rule out lower uterine segment (LUS) placentation in 2nd and 3rd trimesters
    • Transabdominal routine images
      • Midsagittal view
      • Parasagittal views
    • Perform transvaginal ultrasound (TVUS) if LUS not seen with routine views
      • Bleeding is not a contraindication
      • Use careful technique
      • Watch screen while inserting probe
    • Perform translabial/transperineal ultrasound if TVUS not possible
      • Collapsed vagina is acoustic window
      • Elevate maternal hips to minimize bowel artifact
      • Place probe on perineum (labia minora)
  • Is fetus or fluid in direct contact with cervix?
    • Placenta may block direct contact
    • Floating fetus in 3rd trimester
    • Transverse presentation
  • Does the uterus look asymmetrically thick?
    • Placenta & myometrium vs. area with only myometrium
  • Succenturiate lobes often missed
    • Placenta location assigned before uterus completely evaluated
  • Have a high index of suspicion for accreta
    • Suspect accreta if previa & prior cesarean section
      • ↑ Risk with ↑ number of cesarean sections
  • Use color and pulse Doppler
    • Placenta accreta
      • Vessels may extend beyond myometrium
    • Succenturiate lobe
      • Vessels connect placentae
      • Rule out vasa previa
    • Pulse Doppler can help differentiate maternal from fetal vessels
      • Fetal vs. maternal heart rate
Helpful Clues for Common Diagnoses
  • Placenta Previa
    • Subtypes of PP are based on the distance between placenta margin and cervix internal os (IO)
      • Complete PP completely covers IO
      • Partial PP partially covers IO
      • Marginal PP within 2 cm of IO
    • Second trimester PP often resolves
      • Most PP seen < 20 wks resolve by 34 wks
      • 5% PP incidence at 15-16 wks
      • 0.5% PP incidence at term
      • Placental “migration” (trophotropism): Areas of placenta atrophy as others grow
      • LUS “stretches” later in pregnancy
    • Associated with placental abruption
      • Patient presents with bleeding
      • Placental edge lifted by hematoma
      • Mass-like hematoma seen by cervix
    • Associated with preterm labor
      • More common if also bleeding
      • Assess cervical length
      • Assess for IO distention/funneling
      • Cervical canal may be distended with blood
    • 5% of PP will have associated accreta
  • Marginal Sinus Previa
    • Marginal sinus PP is a subtype of marginal PP
    • Evaluate marginal placental vein distance to IO
      • Placental vessels < 2 cm from IO
      • Veins are maternal, not fetal
      • Do not confuse with vasa previa
  • Placenta Accreta Spectrum
    • PA: Pathologic nomenclature based on depth of placental invasion
      • Accreta means myometrial attachment without muscle invasion
      • Increta means myometrial invasion
      • Percreta means invasion through uterus
      • Imaging does not differentiate between subtypes well
    • PP & invasion of cesarean section scar
      • ↓ Subplacental hypoechoic myometrial zone (< 2 mm)
      • Vessels extending through myometrium
    • Distended placental lacunae
      • Bizarre large sonolucencies
      • “Tornado-shaped”
      • Often near PA site
    • MR findings
      • Loss of normal low signal myometrium with T2WI
      • Avoid gadolinium
Helpful Clues for Less Common Diagnoses
  • Succenturiate Lobe
    • SL: Accessory placental lobe or lobes
      • Often smaller than main lobe
    • Identify placental cord insertion site
      • Most often on main lobe
      • May be velamentous (between lobes)
    • Rule out vasa previa
      • Low SL
      • Crossing vessels cover IO
      • At risk for fetal hemorrhage
    • SL is often missed if the entire uterus not imaged
      • 5% of all deliveries have SL
      • Most often asymptomatic and discovered at delivery
      • May present with bleeding if SL previa
      • May present as retained product of conception
Other Essential Information
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Aug 10, 2016 | Posted by in OBSTETRICS | Comments Off on Abnormal Placental Location

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