Placental mesenchymal dysplasia associated with trisomy 13: sonographic findings

Placental mesenchymal dysplasia (PMD) is a rare placental abnormality with sonographic and macroscopic features similar to those seen in a partial hydatidiform mole, and which has usually been reported with a normal female karyotype. We report a case of prenatally suspected PMD associated with trisomy 13. Sonography performed at 17 weeks' gestation showed multiple cystic spaces in the placenta resembling molar tissue, and a fetus with postaxial polydactyly and an atrial septal defect. An amniocentesis revealed a fetal karyotype of 46,XY,der(13), t(13;13)(q11;q11)[20]/47,XY,+13[11], consistent with trisomy 13. Cordocentesis confirmed the cytogenetic diagnosis. Histopathologic examination of the placenta following termination of the pregnancy at 22 weeks' gestation showed enlarged stem villi with loose connective tissue and cistern formation and no evidence of trophoblastic hyperplasia or stromal trophoblastic inclusions, which was consistent with PMD. PMD should be considered in the differential diagnoses of a placenta showing multiple cystic lesions on prenatal sonography, and karyotypic analysis should be performed.