Spectrum of abnormal placental villous adherence

The spectrum of abnormal placental villous adherence describes the degree to which there is an invasion of chorionic villi into the myometrium because of a defect in the decidua basalis.

Pathology

Placental villous adherence is classified on the basis of depth of myometrial invasion:

  • placenta accreta vera: ~75% 
    • mildest form 
    • villi are attached to the myometrium but do not invade the muscle
  • placenta increta: ~20%
    • intermediate form
    • villi partially invade the myometrium
  • placenta percreta: ~5%
    • most severe form
    • villi penetrate through the entire myometrium or beyond serosa 
Risk factors 

Radiographic features

Definite imaging features can vary depending on the extent of invasion.

Ultrasound
  • may show a placenta previa
  • may show "placental lacunae
    • varying sized vascular structures in placenta creating a "moth-eaten" or "swiss cheese" appearance.
    • can be seen as parallel linear vascular channels extending from placental parenchyma into the myometrium: they tend to show turbulent flow (c.f. placental venous lakes show laminar flow)
  • abnormal colour Doppler
    • turbulent flow, i.e. disruption in normal continuous colour flow in myometrium
    • increased vascularity is seen in myometrium, and even in urinary bladder in cases of placenta percreta
  • loss of retroplacental clear space
  • reduced myometrial thickness: anterior myometrial thickness <1 mm
MRI

MR images may show:

  • placenta previa
  • uterine bulging
  • heterogeneous signal intensity within the placenta
  • dark intraplacental bands on T2 weighted images
  • focal interruptions of myometrial wall
  • tenting of the urinary bladder
  • direct visualisation of the invasion of pelvic structures by placental tissue
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Article information

rID: 7781
System: Obstetrics
Section: Pathology
Synonyms or Alternate Spellings:
  • Spectrum of abnormal placental villous attachment
  • Spectrum of abnormal placental implantation
  • Variation in abnormal placental villous adherence

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Cases and figures

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    Normal villous ad...
    Figure 1: normal adherence
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    Placenta accreta
    Figure 2: placenta accreta
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    Placenta increta
    Figure 3: placenta increta
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    Placenta percreta
    Figure 4: placenta percreta
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