Placental lake

Last revised by Dr Jeremy Jones on 20 Sep 2021

Placental (venous) lakes refer to a phenomenon of formation of hypoechoic cystic spaces centrally within the placenta. Finding placental lakes during a second trimester ultrasound scan is not associated with any uteroplacental complication or with an adverse pregnancy outcome. They can, however, be abnormal if very diffuse or if seen very early in pregnancy.

Placental lakes are a common occurrence, reported to occur in approximately 20% of pregnancies.

Their presence tends to be associated with:

They usually result from perivillous fibrin deposition with cystic change within areas of subchorionic fibrin.

  • relatively well defined hypoechoic regions within the placenta
  • color Doppler imaging may show low-velocity intraplacental laminar flow

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Cases and figures

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