2020 Volume 56 Issue 6 Pages 992-997
A female infant was born at the gestational age of 38 weeks and 1 day with a birth weight of 3,036 g. She had an anterior mediastinal cystic mass of 14 mm diameter, which was identified by prenatal ultrasound at 28 weeks of gestation. The size of the cystic mass and internal findings did not change prior to birth. A postnatal computed tomography scan and magnetic resonance imaging showed a heterogeneous mass including a cystic lesion at the right lower pole of the thymus and a homogeneous cystic mass at the left lower pole of the thymus. Both masses were attached at the midline. It was suspected that the teratoma in the right lobe of the thymus perforated and formed a cystic mass in the left lobe. The baby was asymptomatic at birth, but she began to experience a decrease in the level of percutaneous arterial oxygen saturation when crying at 18 days of age. Mass resection with median sternotomy was performed at 22 days of age, and the thymus was preserved. Histopathology revealed that the right mass was a mature teratoma. The left mass was not a perforated cystic lesion, but a unilocular thymic cyst. The postoperative course was uneventful. Various masses arise in the anterior mediastinum, but both teratomas and unilocular thymic cysts are rarely detected prenatally. Moreover, there have been no reports of cases of both conditions occurring concurrently.
