Decidual septal cysts
Placental septa divide and partially support the placenta. They arise from the basal plate and represent furrows or folds in the maternal surface or basal decidua due to placental growth. Fox found septal cysts in 19% of placentae from full-term uncomplicated pregnancies.
- Degeneration of the central decidual cells result in the formation of a cavity filled with homogeneous, fibrinous fluid (Decidual cyst).
- Hemorrhage into the cavity may resemble an intervillous thrombosis.
- Hemorrhage may compress adjacent villi, which may become necrotic and be confused with villous infarction.
- In a pathologically correlated study, 20-40% of cystic or hypoechoic lesions were found to be decidual septal cysts (1).
- Present in approximately 10-20% of placentas from full term uncomplicated pregnancies.
- More common in edematous patients (diabetes mellitus, Rh incompatibility).
Placental infarcts and intervillous thrombosis may produce hypoechoic lesions that are sonographically indistinguishable from a decidual septal cyst.
When there is hemorrhage into a septal cyst, it cannot be distinguished sonographically from an intervillous thrombus.