Department of Gynecology, Félix Guyon Hospital, 97400 Saint-Denis, Réunion Island, France.

This is a cystic lymphangioma of thymic origin:

Fetal ultrasound at 32 weeks revealing a large cyst occupying the top of the upper left hemithorax.

Transverse sonogram of the thorax at 32 weeks, showing the heart and a cyst behind it.

Left parasagittal sonogram of the thorax and the abdomen at 32 weels. The cyst is at the top of the left hemi-thorax and the stomach in its normal place.

Transverse sonogram at 32 weeks at the top of the thorax.

Transverse sonogram at 32 weeks revealing a normal four-chamber heart.

Left parasagittal sonogram of the thorax at 32 weeks. The aorta exit just above the cyst.

Transverse sonogram at the top of the thorax at 37 weeks. We can see a cyst on the left.

Coronal and axial scan prenatal MRI showing a posterior left thoracic mass The right lung seems normal and the stomach is on his normal place.

Baby two days after birth without clinic abnormalities.