Placenta membranacea

Placenta membranacea, also known as a placenta diffusa, is an extremely uncommon variation in placental morphology in which the placenta develops as a thin membranous structure occupying the entire periphery of the chorion.

Epidemiology

The estimated incidence is ~1:20,000-40,000 pregnancies ¹.

Associations

• abnormal placental adherence: reported in up to 30% of cases ¹

Pathology

In this situation all of the fetal membranes are covered by functioning villi and the placenta develops as a thin membranous structure occupying the entire periphery of the chorion. The placental mass can often be thin (1-2 cm ^7,8) and even disrupted.

Radiographic features

Ultrasound

May be seen as a placenta which circumferentially covers most (partial) or all (complete) of the entire uterine wall. May also show accompanying placental thinning and/or disruption.

Complications

Recognized complications include:

• accompanying placenta previa ^6,7

• intra-uterine growth restriction (IUGR)

• recurrent antepartum hemorrhage ²

• second trimester miscarriages

• fetal demise

• postpartum complications

  • postpartum hemorrhage

  • retained placental tissue post delivery