“…In our case, the lesion occupied more than half of the bilateral thoracic cavities and was the largest lesion reported in the literature. Any mass in the thoracic cavity in a fetus requires precise evaluation with fetal ultrasonography and MRI, and its differential diagnoses, other than lymphangioma, include congenital diaphragmatic hernia, teratoma, thymoma, pulmonary sequestration, and bronchogenic and neurogenic cyst . In our case, fetal MRI showed a large mediastinal cyst without a solid component, but did not visualize the septum, which could only be detected by ultrasonography.…”