| Discussion: |
CCAM in the second most common congenital lung lesion. It is usually due to an embryological insult the 5th-7th week of gestation, involving malformation of the terminal bronchiolar structures. Its features include a single lobe of one lung being enlarged and cystic, compressing the remainder of that lung. It then compresses the contralateral lung via a mediastinal shift. The remaining ipsilateral lung may be hypoplastic due to the space-occupying nature of the lesion.
Type I (50%):
Histology shows single or multiple large cysts (>20mm) which are lined by respiratory epithelium. It has an excellent prognosis.
Type II (40%):
Histology is remarkable for multiple cysts (5-12mm) lined by ciliated cuboidal/columnar epithelium. It has a poor prognosis secondary to associated abnormalities.
Histology shows a large mass of microcysts (3-5mm) lined by ciliated cuboidal epithelium. It also has a poor prognosis.
CCAM can be diagnosed in utero by ultrasonography. It is most likely to be seen between the 18th-36th weeks of gestation. It was found that 25% of these fetuses also had associated secondary abnormalities: renal agenesis/polyhydramnios, cardiac malformation, pectus excavatum, jejunal atresia, chromosomal anomalies, prune-belly syndrome, and bronchopulmonary sequestration.
Common postnatal complications include: neonatal respiratory distress, recurrent respiratory tract infections, and pneumothorax. 50% are born prematurely and 25% are stillborn. The presence of polyhydramnios, ascites, or hydrops indicates a poorer prognosis. Patients may also be at an increased risk for developing primary pulmonary neoplasms.
CCAM occurs with equal frequency in all lung lobes. It is usually unilateral. Rarely affected is the middle lobe.
Physical exam will be remarkable for decreased breath sounds on the affected area with mediastinal shift away from the lesion.
CXR will show multiple air or fluid-filled cysts with compression of the adjacent lung. There will be contralateral mediastinal shift. The ipsilateral lung will be hypoplastic. Abdominal viscera will be in correct position. In a type III lesion, there will also be a unilateral mass with well-defined margins.
CT will also show single or multiple air/fluid-filled cysts with thin walls. There will also be surrounding emphysematous changes.
OB ultrasound will show the cysts as well as the contralateral mediastinal shift. The level of amniotic fluid will also be assessed for the presence of poly/oligo-hydramnios. The presence of fetal ascites or hydrops can also be evaluated.
Treatment involves surgical resection of the affected lobe/segment.