Placental Mesenchymal Dysplasia: A Confusing Entity and the Definitive Role of Histopathology

Background: Placental mesenchymal dysplasia (PMD) is a rare placental disease of poorly understood etiology. It is characterized by aneurysmal dilatation of the chorionic blood vessels, mesenchymal proliferation, and myxomatous degeneration of the stem villi. Although it shares radiological and gross pathological features with partial hydatidiform mole, PMD doesn't necessitate termination of pregnancy. Case presentation: A 20-year-old woman presented at 25 weeks of gestation with profuse vaginal bleeding and loss of sensation of fetal movements. Abdominal ultrasound revealed a dead fetus and a markedly thick placenta which contains frequent hypoechoic cystic spaces creating a Swiss cheese appearance. Serum β -HCG was within the normal range as regards the gestational stage. A gross examination of the placenta revealed dilated tortuous blood vessels with frequent aneurysms on the placental surface and the cut section showed clotted blood. No definite vesicles were seen. Histopathological evaluation of the placental tissue revealed a mixture of normal and dilated villi with thick chorionic blood vessels and myxomatous degeneration of the villous cores. There was no trophoblastic proliferation, features were kept with PMD. Conclusion: Placental mesenchymal dysplasia is a rare placental disease that is usually confused with partial hydatidiform mole at both radiological and gross pathological features. However, histopathological examination helps in adopting an accurate diagnosis.