Prenatal ultrasound is indispensable to screen for congenital disorders in the fetus. Today, we will talk about the common fetal abnormalities in prenatal ultrasound – cystic lung tumor. Prenatal ultrasound shows an occupancy of the thoracic cavity, with severe fetal mediastinal displacement, pericardial effusion, fetal edema, and excessive amniotic fluid. The greatest effects of this occupancy on the fetus are the disruption of normal lung tissue development, compression of the heart and great vessels causing impaired fetal circulation, and compression of the esophagus causing impaired swallowing of amniotic fluid. These effects depend on the size of the occupancy. Once the size of the occupancy is large, mediastinal displacement, obstruction of venous return, and damage to the heart occur, fatal edema can result. Pulmonary cystic tumors are usually in a relatively stable state by 28 weeks of fetal life. The likelihood of fetal edema can be predicted clinically based on the child’s cvr value. The threshold value is 1.6, and above 1.6, the likelihood of edema is greatly increased, suggesting a poor prognosis. Found before 28 weeks, weekly ultrasound is recommended to calculate the cvr value. In about 25% of cases, they shrink or even disappear completely. For large single cysts cystocentesis is feasible to aspirate the intracapsular fluid, which has the effect of emergency decompression to avoid the development of edema. Surgical removal of the fetus has also been performed. Smaller cystic adenomas can be diagnosed and then surgically removed after the birth of the fetus. To avoid recurrent respiratory infections and related complications, surgical resection should be performed once the diagnosis is confirmed.