Type III congenital cystic adenomatoid malformation of the lung detected through maternal serum screening positive for Down's syndrome

A 24 year old primigravida was referred for genetic counseling because of an abnormal maternal serum result which indicated a Down's syndrome risk of 1:59 calculated from the gestational age, maternal age, a maternal serum alpha-fetoprotein (AFP) value of 32.50 ng/ml or 0.64 multiples of the median (MoM), and a human chorionic gonadotrophin (hCG) value of 130.30 IU/ml or 3.84 MoM (EIA, AFP, hCG; Abbott Laboratories, Inc., North Chicago, IL, USA) at 17 weeks' gestation. The gestational age was confirmed by ultrasonography. The estimated risk of Down's syndrome during the second trimester at a maternal age of 24 years is 1:942. A maternal serum screening result with a calculated risk of greater than 1:270 is deemed 'screen-positive' and a recommendation for diagnostic amniocentesis is initiated. Ultrasonographic examination at 19 weeks' gestation during genetic amniocentesis revealed a single fetus with an estimated gestational age of 19 weeks, and a large echogenic mass within the left hemi-thorax. The mediastinum was displaced to the right. No polyhydramnios, fetal hydrops, fetal ascites, or associated structural abnormalities were noted. A tentative diagnosis of Type III congenital cystic adenomatoid malformation of the lung (CCAML) was made. Cytogenetic analysis revealed a 46,XY karyotype. The amniotic fluid AFP level was 7316 ng/ml, 1.37 MoM at 19 weeks' gestation. The parents were nonconsanguineous and healthy. Then was no family history of congenital malformations. The maternal blood group was O, Rh-positive and the maternal thalassemia, syphilis, and hepatitis B screen results were negative. The mother was followed up by serial obstetric ultrasonography which confirmed the persistent appearance of an echogenic fetal lung. At 23 weeks' gestation, the fetal thoracic circumference measured 17.9 cm, the echogenic mass circumference measured 11.0 cm, the area of the fetal thorax 24.6 cm(2), and the area of the echogenic mass 10.2 cm(2). The echogenic mass occupied 42% of and the area of fetal thorax. The unilateral echogenic mass in the fetal thorax was felt to be consistent with type III CCAML. There were lateral displacement of the fetal heart, the tumor involvement of the left lung, and compression of the right lung but without coexistent polyhydramnios or fetal hydrops (Fig. 1). The parents opted to terminate the pregnancy at 24 weeks' gestation. A male fetus weighing 706 g was delivered with no external morphological abnormalities. Necropsy revealed that the entire left hemi-thorax was occupied by a greatly enlarged left lung which displaced the heart and compressed the right lung. Microscopically, the upper and lower lobes of the left lung showed the characteristic histological appearance of type III CCAML. The parenchyma comprised small cysts resembling expanded terminal bronchioles lined with cuboidal epithelium. No cartilage plates or mucogenic cells could be identified. Examination of the placenta revealed neither hydatidiform mole nor hydropic degeneration.