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.

  • placenta accreta:
    • commonest type of placental invasion (~75% of cases)
    • occurs in ~1 in 7,000 pregnancies
    • combination of previous C-section and an anterior placenta praevia raises the probability of a placenta accreta
    • maternal mortality of up to 7% depending on location
  • placenta increta:
    • ~25% cases
    • occurs in ~1 in 50,000 pregnancies
  • placenta percreta:
    • ~5% cases

The incidence of all forms of abnormal placental villous adherence is increasing, which is felt to be due to the increased practice of caesarean sections

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

  • placenta accreta:
    • mildest form 
    • villi are attached to the myometrium but do not invade the muscle
  • placenta increta:
    • intermediate form
    • villi partially invade the myometrium
  • placenta percreta:
    • severest form
    • villi penetrate through the entire myometrium or beyond serosa 

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

  • may show placenta praevia
  • may show placental lacunae
    • variably-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 (cf. placental venous lakes show laminar flow)
  • abnormal colour Doppler
    • turbulent flow, i.e. disruption of the normal continuous colour flow in the myometrium
    • increased vascularity is seen in the myometrium, and even in the urinary bladder in cases of placenta percreta
  • loss of retroplacental clear space
  • reduced myometrial thickness: anterior myometrial thickness <1 mm

MR images may show:

  • placenta praevia
  • 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
Synonyms or Alternate Spellings:
  • Spectrum of abnormal placental villous attachment
  • Spectrum of abnormal placental implantation
  • Variation in abnormal placental villous adherence

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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