Placental venous lakes

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.

Epidemiology

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

Pathology

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

Associations

Their presence tends to be associated with:

• increased placental thickness
• placenta accreta spectrum and abnormal placental villous adherence
• placental insufficiency, especially if seen early in pregnancy ⁵

Markers

• the presence of placental lakes is associated with increased maternal serum alpha-fetoprotein (MSAFP) levels

Radiographic features

Antenatal ultrasound

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

Differential diagnosis

• placental chorioangioma: shows marked internal vascularity on colour Doppler imaging