Contributed by Lauren Brilli Skvarca, MD, PhD, Stefan Kostadinov, MD
The patient is an approximately 30-year-old primigravida with an intrauterine dichorionic-diamniotic twin pregnancy. Prenatal ultrasound at 30 weeks gestation showed a multi-cystic mass without fetal parts suspicious for hydatidiform mole (twin A), and one live fetus with normal anatomy (twin B) with a corresponding enlarged, cystic placenta (placenta B). At 36 weeks gestation, the mother developed preeclampsia and preterm labor and delivered one live, morphologically normal female infant (twin B) weighing in the less than tenth percentile. The infant was transferred to the NICU after delivery for low birthweight and prematurity.
The specimen submitted to pathology, representing twin A plus placenta B, weighed in the greater than ninetieth percentile for a twin gestation. Gross examination showed a 15 x 8 x 3 cm portion of multi-cystic, grape-like tissue (twin A) loosely attached to the disc of placenta B at the margin. Placenta B disc measured 24 x 20 x 5 cm and demonstrated aneurysmally dilated and partly thrombosed chorionic fetal vessels and randomly scattered parenchymal cysts. Specimen radiographs did not show fetus papyraceus. Histologic examination of the multi-cystic tissue (twin A) demonstrated hydropic villi with trophoblast hyperplasia. p57 immunostaining showed loss of expression in villous cytotrophoblast. Histologic examination of placenta B demonstrated both cystically dilated stem villi with hypercellular, myxoid stroma containing abnormally thickened stem-villous vessels and interspersed normal appearing villi. Terminal villi did not show hydropic features. Villous cytotrophoblast showed normal proliferation and were p57-positive. While there was loss of p57 expression in the stromal cells of cystically dilated stem villi, p57 expression was maintained in stromal cells of normal villi.