[Cystic degeneration of placental subchorionic intervillous thrombi].

This is a case study of a 31 year-old woman who presented for a routine follow-up examination at 33 weeks of gestation. A 9-cm intrauterine membranous cystic structure, floating in the amniotic fluid, with 3 internal round structures attached on a stalk in close proximity to the placental insertion of the umbilical cord was demonstrated in sonography. A color Doppler study of the cyst was normal and also revealed a normal systolic/diastolic flow ratio in the umbilical arteries. The cyst was not reported on extended sonographic scans at 15 weeks and 24 weeks gestation. The patient delivered spontaneously at term giving birth to a 3300 grams healthy newborn. The pathologic diagnosis was cystic degeneration of subchorionic intervillous thrombi.