Atelectasis Or Collapse Of The Lung may be either congenital or acquired. The congenital or fetal form occurs in newborn babies who have never breathed, either on account of an obstruction to a bronchus or from lack of strength. The entire lung or portions only may be involved. Obstruction of the upper air-passages by meconium or amniotic fluid will cause atelectasis.

The acquired form develops after expansion has once taken place, and may result from pressure from the outside, as in pleuritic effusions, neoplasms, etc., or it may follow obstruction of a bronchus with absorption of the contained air, the vesicles then collapsing. The involved area varies in color, according to the amount of blood present, from a pale red to a dark brownish color. The lung will be pale when the atelectasis is due to pressure from the outside. The tissue is dense, dry, tough, does not contain air, and will not crepitate; will sink when placed in water. If there is much congestion, the tissue looks like meat and the condition is termed carni-fication. If the atelectasis has existed for some time, there is proliferation of fibrous connective tissue, giving rise to an appearance resembling the spleen, known as splenization. Inflammation, with fibrosis and the deposit of lime salts, may occur in the involved area.