A fetus with large mediastinal cystic lymphatic malformation managed with prenatal serial thoracocentesis and postnatal sclerotherapy

We report a very rare case of large fetal mediastinal cystic lymphatic malformation (cLM), formerly called lymphangioma, that was managed with prenatal serial thoracocentesis and postnatal sclerotherapy. A fetal pericardial effusion‐like lesion gradually increased the size until it occupied more than half of the thoracic cavity. Thoracocentesis was performed three times, namely at 31 and 35 weeks of gestation, and also just before the delivery for decompression. The characteristic shape changes of the lesion were observed after thoracocentesis. A boy delivered by planned cesarian section at term required respiratory support after birth. Postnatal magnetic resonance imaging (MRI), which showed a large cystic lesion with septa and hemorrhage without solid components, led to the diagnosis of cLM. The fluid from the cyst continued to be drained. Neonatal sclerotherapy using OK‐432 was effective and the infant recovered well. Fetal thoracocentesis may be useful for the diagnosis and management of a large mediastinal cLM.