Polyalveolar lobe and congenital cystic adenomatoid malformation type II: are they related?

A left lower polyalveolar lobe in a 28-day-old infant and a right lung with congenital cystic adenomatoid malformation type II in a 17-day-old infant are described. The adenomatoid malformation involved all lobes, but the lower lobe appeared to be mostly replaced by a polyalveolar area, a complication hitherto undescribed. The pronounced increase in number of alveoli in both cases was established by two different morphometric methods and was compared with three normal controls of the same age. The simultaneous occurrence of polyalveolar lobe and congenital cystic adenomatoid malformation type II in the same lung suggests a causal relation between both anomalies. In the grossly abnormal lung tissue of an adenomatoid malformation, polyalveolar areas can easily be overlooked.