Objective To summarize the prenatal ultrasonography characteristics of congenital cystic adenomatoid malformation（CCAM） and determine its prognosis.Methods Forty-six fetuses with prenatally diagnosed CCAM using ultrasound were selected and classified according to the size of their cysts.The prenatal ultrasonographic features

thoracic indicators

whether complicated with mediastinal shifts

polyhydramnios

fetal edema or hydrops and other malformations were analyzed and compared

and follow-up volume changes and prognosis.Results Forty-six CCAM fetuses were divided into9 cases of large capsule type（type Ⅰ）

22 cases of medium capsule type（type Ⅱ） and 15 cases of microcapsule type（type Ⅲ）according to the size of their cysts.①Prenatal ultrasonography characteristics of CCAM:lesions were located in unilateral thorax in 43 cases and bilateral thorax in 3 cases.The CCAM volume ratio（CVR） was gradually increased but lung volume to thoracic volume ratio was gradually decreased in three CCAM types

the difference was statistically significant（all P<0.05）

while there were no significant differences in mass volume

thoracic transverse diameter

anteroposterior diameter

chest area

chest circumference

lung volume and thoracic volume.②Complications of CCAM:the presence or absence of polyhydramnios

fetal edema and hydrops were different among different types

type Ⅲ was the most

and type Ⅰ was the least（P<0.05）

while there were no statistically significant differences in mediastinal shift

other malformations and decreased mass size at follow-up.③Prognosis of CCAM:the pregnancy outcomes were different in different types

type Ⅲ was the worst（P<0.05）

while there were no statistically significant differences in postpartum intervention.The prognosis of fetuses complicated with edema was poor.Conclusion Prenatal ultrasonography characteristics of CCAM is typical.The classification of CCAM is related to the size of cyst

CVR

lung volume to thoracic volume ratio and complications.Prenatal ultrasound can evaluate the prognosis according to the types and complications

type Ⅲ is worse than type Ⅰ and type Ⅱ.