Atelectasis

Atelectasis refers to a decrease in volume or air content of one or more pulmonary segments or lobes. Due to absorption of alveolar gas, atelectasis is usually accompanied by reduced radiolucency in the affected area, with adjacent structures (bronchi, pulmonary vessels, pulmonary interstitium) converging toward the collapsed region; alveolar consolidation may sometimes be observed, and other lung tissue may show compensatory emphysema. Collateral gas communication between pulmonary lobules, segments (and occasionally lobes) may allow a completely obstructed area to retain a certain degree of radiolucency. Atelectasis can be classified as congenital or acquired. Congenital atelectasis refers to the absence of gas filling in the alveoli at birth, clinically presenting with severe dyspnea and cyanosis, and affected infants often die of severe hypoxia shortly after birth. The vast majority of clinical atelectasis is acquired.