Disappearing fetal lung masses: importance of postnatal imaging studies

Background. The “disappearance” of congenital masses of the lung on prenatal sonograms has been described, but the importance of postnatal imaging studies in these children is unknown. Objective. The objective of this work was to study the utility of radiographs and CT scans in asymptomatic infants with congenital masses of the lung that partially or completely resolve on prenatal sonograms performed late in gestation. Materials and methods. The prenatal sonograms, postnatal imaging studies, surgical findings, and pathologic diagnoses of seven children with an echogenic mass of the lung that improved or disappeared on prenatal sonograms were reviewed. Results. All masses were type II congenital cystic adenomatoid malformation, with features of intralobar sequestration also being found in four. An unsuspected extralobar sequestration adjacent to a left lower lobe mass was found at surgery in one patient. All masses were hyperechoic compared with normal lung on sonograms prior to 32 weeks of gestation, with cysts being seen in four. On scans after 32 weeks, four of the masses had resolved completely and three showed subtle increased echogenicity compared with normal lung. Cysts completely resolved in two of four cases. Postnatal radiographs showed subtle abnormalities in four infants, a hyperlucent lobe in one, a soft tissue mass with adjacent hyperlucency in one, and normal findings in one. CT scans were abnormal in all cases, with air-filled cysts and soft tissue in six and a hyperinflated lobe in one. Conclusion. Children with “disappearing” fetal lung masses have persistent abnormalities after birth that are often subtle on radiographs but are well demonstrated with CT.