Mesenchymal dysplasia of the placenta: a rare entity and important differential diagnosis. Presentation of a case with placentomegaly.

Placental mesenchymal dysplasia (PMD) is a rare disease with unclear etiology and peculiar placental findings (placentomegaly, abnormal chorionic vessels with thromboses, and grossly enlarged and often cystic-appearing stem villi). Songraphic findings are cystic changes, hypoechoic areas, placental enlargement, and dilated chorionic vessels.PMD can be associated with severe perinatal complications, e.g., intrauterine fetal demise, fetal growth restriction, and preterm delivery. Neonatal complications include Beckwith-Wiedemann Syndrome (BWS), hepatic tumors, and hematologic diseases, i.e., anemia and thrombocytopenia. However, in a minority of cases the mothers and children display no perinatal or postnatal findings. It is important to be aware of the entity because it can be mistaken for molar pregnancy (with a different clinical procedure) on routine ultrasound investigation. Maternal alpha-fetoprotein serum levels are often increased in the case of PMD.We report a case of PMD with typical entity-related findings on ultrasound investigation and striking pathological-anatomic findings such as massive placentomegaly and prominent thromboses of the tortuous chorionic vessels but without perinatal or postnatal complications.