Placental lakes are enlarged spaces in the placenta filled with maternal blood. These spaces are also called intervillous spaces because they are found between the placental villi the finger-like projections of the placenta that contain fetal blood vessels . The placental villi float in the intervillous spaces and absorb oxygen and nutrients from the maternal blood.

The blood-filled placental lakes appear nearly black (white arrows) on ultrasound because they do not reflect soundwaves back to the ultrasound machine. Placental lakes can be seen within the placenta or on the fetal surface of the placenta bulging into the amniotic cavity. Slow swirling blood flow (larger arrow) may be seen within the spaces, and the shape of the spaces tends to change with uterine contractions. These features may help to distinguish a placental lakes from a thrombus.

Placental lakes are considered to be a normal finding in most cases. However, multiple placental lakes seen early in pregnancy have been associated with fetal growth restriction. The differential diagnosis of multicystic placental lesions includes, but is not limited to, molar pregnancy, chorioangioma, subchorionic hematoma, and spontaneous abortion with hydropic placental changes. In a patient with placenta previa and previous uterine surgery multiple placental lakes should raise suspicion for placenta accreta or percreta.

Multiple placental lakes with a thickened placenta suggests gestational trophoblastic disease or placental mesenchymal dysplasia (PMD). The latter is asociated with elevated maternal serum alpha fetoprotein .

Synonyms: Placental vascular lacunae, placental caverns, placental venous lakes, placental sonolucencies.

REFERENCES

Reis NS, et al. Placental lakes on sonographic examination: correlation with obstetric outcome and pathologic findings.J Clin Ultrasound. 2005;33(2):67-71.PMID: 15674837

Thompson MO,; et al. Are placental lakes of any clinical significance?Placenta. 2002;23(8-9):685-90.PMID: 12361687

Jauniaux, E. and Nicolaides, K. H. 1996. Placental lakes, absent umbilical artery diastolic flow and poor fetal growth in early pregnancy.Ultrasound Obstet Gynecol. 1996 ;7(2):141-4.PMID: 8776240

Nayeri UA, et. al. Systematic review of sonographic findings of placental mesenchymal dysplasia and subsequent pregnancy outcome.Ultrasound Obstet Gynecol. 2013 Apr;41(4):366-74. PMID: 23239538