Congenital Cystic Adenomatoid Malformation (CCAM/CPAM)

A 28-year-old G2P1 woman at 24 weeks gestation undergoes targeted fetal ultrasound for evaluation of a thoracic mass detected on routine anomaly scan. The axial view of the fetal thorax shows a large heterogeneous multicystic echogenic mass marked **A** occupying the right hemithorax with multiple cysts ranging from 5 to 25 millimeters in diameter. The CVR (cyst volume to head circumference ratio) is 2.1, and there is evidence of early fetal ascites and skin edema. The arterial supply to the mass is from the pulmonary artery. Which of the following best describes the embryologic basis and classification of the lesion marked **A**?