The progression of mediastinal lymphangioma in utero.

We describe a case of mediastinal lymphangioma that suddenly progressed in utero. The initial sonographic impression was one of pericardial effusion while the follow-up examination revealed a mediastinal cystic mass. At 35 weeks of gestation preterm labor occurred. An ultrasound examination performed at this time demonstrated the mediastinal cyst with internal hemorrhage and fetal hydrops. The cystic mass was resected 5 days after birth. The diagnosis of lymphangioma was made from histological examination. The infant was followed up for 18 months and remained well. We recommend frequent prenatal sonographic follow-up when a localized fluid collection is, shown in the mediastinum.