Mesenchymal Dysplasia in a Monochorionic Diamniotic Twin Pregnancy With Review of the Differential Diagnosis of Cystic Changes in the Placenta

Placental mesenchymal dysplasia (PMD) is a distinct syndrome of unknown etiology that is associated with substantial fetal morbidity and mortality. It is characterized by an enlarged, hydropic placenta, depicting multiple cysts and tangles of intestinelike chorionic vessels on gross examination. The sonographic features are usually suggestive of a partial mole. Intrauterine growth restriction (IUGR) is common, yet, paradoxically, Beckwith-Wiedemann syndrome (BWS) has been diagnosed in many fetuses and neonates. Cystic changes in the placenta are relatively uncommon findings and are mostly related to chorioangiomas or trophoblastic disease. We report an early second-trimester (16 weeks' gestation) diagnosis of PMD in a monochorionic diamniotic twin pregnancy. There are fewer than 100 reported PMD cases in the literature.1 A review of the etiology of cystic changes of the placenta is presented, with emphasis on maternal and fetal aspects as well as genetic counseling and other tests to be considered. We expand on the differential diagnosis and implications of diffuse cystic changes in the placenta.