I. What is congenital cystic adenoma of the lung? 1, Congenital cystic adenomatoid malformation (CCAM), commonly known as pulmonary cystadenoma, now called congenital pulmonary airway malformation (CPAM), and tracheopulmonary segregation (BPS), congenital lobar emphysema (CLE) with combined bronchial atresia, etc., are congenital lung masses and belong to the same spectrum of disease. 2. Pulmonary cystic adenoma CPAM is a misshapen lesion consisting of cystic and adenomatous components originating from tracheal, bronchial, fine bronchial or alveolar tissue. Larger lesions may compress adjacent normal tissues, thereby impairing alveolar growth and development. 3. CPAM is divided into five types, and the prenatal course depends more on gestational age, size of the mass, degree of mediastinal displacement, fetal hemodynamics, and concomitant abnormalities than on the type of lesion. Most CPAM grows rapidly and progressively at 20-26 weeks of gestation, peaking at about 25 weeks, and then stops growing and often regresses. The growth rate of large cystic lesions is slower. Both microcystic and macrocystic lesions can develop into edema and require prenatal intervention. There are no reliable criteria to determine whether a lesion continues to grow, stabilizes, or regresses. 2. About 50% of masses will persist until delivery. Fifteen percent of masses become smaller in size at the end of mid- and late-term pregnancies; most decrease in size relatively due to normal fetal thoracic growth, but a few increase in size. As the mass decreases in size, its echogenicity resembles that of the surrounding normal lung tissue. This is due to enhanced normal lung echogenicity and diminished CPAM echogenicity. On T2-weighted MRI, the signal intensity is lower than that of normal lung tissue as the lesion subsides. Persistent masses can be confirmed on postnatal imaging in more than 95% of cases. 3. In 50% of cases, the mass appears to regress before birth, which usually occurs in cases with small cystic lesions and low CVR. Sixty percent of patients whose ultrasound showed regression of the prenatal lesion had no abnormality on postnatal imaging. The cause of the abnormality seen in these cases may not be CPAM but transient bronchial tree obstruction with fluid retention, or the lesion’s blood supply may not be adequate for its overgrowth or the lesion may show spontaneous torsion. The remaining 40% of masses that show regression prenatally persist after birth; this is due to the normal enhancement of lung echogenicity in late pregnancy, which makes it difficult to distinguish between normal and abnormal lung tissue and therefore misses these cases prenatally. III. Prenatal evaluation 1. At initial ultrasound, it is difficult to predict whether the lesion will regress, remain stable, or continue to grow and cause a number of serious consequences, including edema, the need for surgical intervention or assisted ventilation after birth, and death. A CVR >1.6 indicates a greater risk of edema, respiratory distress at birth, and possible need for early surgery, whereas a CVR <0.91 at the time of presentation predicts a better outcome and therefore allows for less frequent follow-up examinations. an MTR <0.51 indicates a lower risk of fetal complications. A study showed that a lungmassvolumeratio (LMVR) >1.3 measured by fetal MRI predicted neonatal respiratory distress (89% vs 7% when LMVR<1.3). 3. In the absence of edema, the prognosis is good, with a reported live birth rate of ≥95%. When edema occurs, the prognosis is poor. 4, The presence of edema in the fetus is the most important predictor of poorer outcome: without intervention, the risk of perinatal death in cases of edematous fetuses approaches 100%. Cases of spontaneous regression of early edema (pleural effusion and/or ascites) without intervention have also been reported, but are extremely rare. 5. Edema occurs in up to 1/3 of CPAM fetuses due to hemodynamic changes caused by vena cava obstruction and cardiac displacement/compression. Fetuses with large lesions, lesions that persist into late pregnancy, and lesions that are microcystic are at highest risk. 6. Another complication of fetal edema is the combined maternal mirror syndrome, which manifests as maternal generalized edema, often involving the lungs, in a mirror image relationship with the edema of the fetus and placenta. 7. Since 10%-20% of CPAM fetuses are combined with congenital anomalies, a comprehensive fetal workup, including echocardiography, should be performed. Combined congenital anomalies include esophageal atresia with combined tracheoesophageal fistula, bilateral renal agenesis or dysplasia, intestinal atresia, other pulmonary anomalies. anomalies, as well as diaphragm, heart, central nervous system, and skeletal anomalies. 4. prediction of fetal edema 1. if edema has not occurred by about 28 weeks, it is unlikely to occur later because the CPAM does not continue to grow at the end of midterm pregnancy and the fetal thorax continues to expand. edema does not occur after the CPAM no longer continues to grow. 2. In patients at higher risk of edema, fetal echocardiography can be used to assess whether cardiac compression restricts ventricular filling and leads to inferior vena cava flow reversal. Although data are only available from small case series studies, a threshold CVR of 1.6 at the time of presentation appears to distinguish whether edema occurs. A case series study that included 58 CPAM fetuses showed a 7/42 (17%) incidence of fetal edema with a CVR ≤1.6 and a 40/42 (94%) fetal survival rate after intervention, and a 12/16 (75%) incidence of fetal edema with a CVR >1.6 and a 9/16 (56%) fetal survival rate after intervention. a CVR ≤1.6 and no significant cystic The incidence of edema was only 1/36 (2.8%) in fetuses with a CVR ≤1.6 and no significant cystic mass. 3. A 10-year retrospective case series study included 128 fetuses with congenital lung masses and found that LMVR >2.0 measured by fetal MRI was predictive of edema (42% vs 2% when LMVR <2.0) and heart failure (32% vs 2% when LMVR <2.0).